[media] doc-rst: improve display of notes and warnings
There are several notes and warning mesages in the middle of the media docbook. Use the ReST tags for that, as it makes them visually better and hightlights them. While here, modify a few ones to make them clearer. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
This commit is contained in:
Mauro Carvalho Chehab
parent
fed7b888f6
commit
706f8a9975
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@ -32,7 +32,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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Closes the cec device. Resources associated with the file descriptor are
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@ -38,7 +38,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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The :c:func:`ioctl()` function manipulates cec device parameters. The
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@ -45,7 +45,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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To open a cec device applications call :c:func:`open()` with the
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@ -29,7 +29,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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With the :c:func:`poll()` function applications can wait for CEC
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@ -3,7 +3,7 @@
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Introduction
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============
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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HDMI connectors provide a single pin for use by the Consumer Electronics
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@ -31,7 +31,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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All cec devices must support the :ref:`CEC_ADAP_G_CAPS` ioctl. To query
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@ -35,7 +35,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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To query the current CEC logical addresses, applications call the
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@ -34,7 +34,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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To query the current physical address applications call the
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@ -32,7 +32,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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CEC devices can send asynchronous events. These can be retrieved by
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@ -30,7 +30,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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By default any filehandle can use
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@ -33,7 +33,7 @@ Arguments
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Description
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===========
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Note: this documents the proposed CEC API. This API is not yet finalized
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.. note:: This documents the proposed CEC API. This API is not yet finalized
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and is currently only available as a staging kernel module.
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To receive a CEC message the application has to fill in the
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@ -15,8 +15,9 @@ The information about the frontend tuner locking status can be queried
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using :ref:`FE_READ_STATUS`.
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Signal statistics are provided via
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:ref:`FE_GET_PROPERTY`. Please note that several
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statistics require the demodulator to be fully locked (e. g. with
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FE_HAS_LOCK bit set). See
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:ref:`FE_GET_PROPERTY`.
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.. note:: Most statistics require the demodulator to be fully locked
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(e. g. with FE_HAS_LOCK bit set). See
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:ref:`Frontend statistics indicators <frontend-stat-properties>` for
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more details.
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@ -8,7 +8,7 @@
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Digital TV API
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##############
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**NOTE:** This API is also known as **DVB API**, although it is generic
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.. note:: This API is also known as **DVB API**, although it is generic
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enough to support all digital TV standards.
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**Version 5.10**
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@ -20,7 +20,7 @@ Also, the union didn't have any space left to be expanded without
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breaking userspace. So, the decision was to deprecate the legacy
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union/struct based approach, in favor of a properties set approach.
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NOTE: on Linux DVB API version 3, setting a frontend were done via
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.. note:: On Linux DVB API version 3, setting a frontend were done via
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:ref:`struct dvb_frontend_parameters <dvb-frontend-parameters>`.
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This got replaced on version 5 (also called "S2API", as this API were
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added originally_enabled to provide support for DVB-S2), because the
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@ -93,7 +93,7 @@ Example: Setting digital TV frontend properties
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return 0;
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}
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NOTE: While it is possible to directly call the Kernel code like the
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.. attention:: While it is possible to directly call the Kernel code like the
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above example, it is strongly recommended to use
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`libdvbv5 <https://linuxtv.org/docs/libdvbv5/index.html>`__, as it
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provides abstraction to work with the supported digital TV standards and
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@ -9,7 +9,7 @@ Examples
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In this section we would like to present some examples for using the DVB
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API.
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NOTE: This section is out of date, and the code below won't even
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..note:: This section is out of date, and the code below won't even
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compile. Please refer to the
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`libdvbv5 <https://linuxtv.org/docs/libdvbv5/index.html>`__ for
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updated/recommended examples.
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@ -36,7 +36,8 @@ Arguments
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Description
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===========
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WARNING: This is a very obscure legacy command, used only at stv0299
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.. warning::
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This is a very obscure legacy command, used only at stv0299
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driver. Should not be used on newer drivers.
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It provides a non-standard method for selecting Diseqc voltage on the
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@ -144,7 +144,7 @@ struct dvb_frontend_info
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- Capabilities supported by the frontend
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NOTE: The frequencies are specified in Hz for Terrestrial and Cable
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.. note:: The frequencies are specified in Hz for Terrestrial and Cable
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systems. They're specified in kHz for Satellite systems
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@ -40,7 +40,7 @@ used to check about the locking status of the frontend after being
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tuned. The ioctl takes a pointer to an integer where the status will be
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written.
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NOTE: the size of status is actually sizeof(enum fe_status), with
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.. note:: The size of status is actually sizeof(enum fe_status), with
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varies according with the architecture. This needs to be fixed in the
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future.
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@ -42,10 +42,10 @@ to send a 22kHz tone in order to select between high/low band on some
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dual-band LNBf. It is also used to send signals to DiSEqC equipment, but
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this is done using the DiSEqC ioctls.
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NOTE: if more than one device is connected to the same antenna, setting
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a tone may interfere on other devices, as they may lose the capability
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of selecting the band. So, it is recommended that applications would
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change to SEC_TONE_OFF when the device is not used.
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.. attention:: If more than one device is connected to the same antenna,
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setting a tone may interfere on other devices, as they may lose the
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capability of selecting the band. So, it is recommended that applications
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would change to SEC_TONE_OFF when the device is not used.
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.. _fe-sec-tone-mode-t:
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@ -48,9 +48,9 @@ the ones that implement DISEqC and multipoint LNBf's don't need to
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control the voltage level, provided that either 13V or 18V is sent to
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power up the LNBf.
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NOTE: if more than one device is connected to the same antenna, setting
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a voltage level may interfere on other devices, as they may lose the
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capability of setting polarization or IF. So, on those cases, setting
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.. attention:: if more than one device is connected to the same antenna,
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setting a voltage level may interfere on other devices, as they may lose
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the capability of setting polarization or IF. So, on those cases, setting
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the voltage to SEC_VOLTAGE_OFF while the device is not is used is
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recommended.
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@ -29,7 +29,7 @@ The frontend can be accessed through ``/dev/dvb/adapter?/frontend?``.
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Data types and ioctl definitions can be accessed by including
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``linux/dvb/frontend.h`` in your application.
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NOTE: Transmission via the internet (DVB-IP) is not yet handled by this
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.. note:: Transmission via the internet (DVB-IP) is not yet handled by this
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API but a future extension is possible.
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On Satellite systems, the API support for the Satellite Equipment
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@ -92,10 +92,12 @@ Generic Error Codes
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- Permission denied. Can be returned if the device needs write
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permission, or some special capabilities is needed (e. g. root)
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.. note::
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Note 1: ioctls may return other error codes. Since errors may have side
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effects such as a driver reset, applications should abort on unexpected
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errors.
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#. This list is not exaustive; ioctls may return other error codes.
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Since errors may have side effects such as a driver reset,
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applications should abort on unexpected errors, or otherwise
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assume that the device is in a bad state.
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Note 2: Request-specific error codes are listed in the individual
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#. Request-specific error codes are listed in the individual
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requests descriptions.
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@ -251,7 +251,9 @@ I/O control requests
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be useful of receivers that have otherwise narrow band receiver that
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prevents them to be used with some remotes. Wide band receiver might
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also be more precise On the other hand its disadvantage it usually
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reduced range of reception. Note: wide band receiver might be
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reduced range of reception.
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.. note:: Wide band receiver might be
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implictly enabled if you enable carrier reports. In that case it
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will be disabled as soon as you disable carrier reports. Trying to
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disable wide band receiver while carrier reports are active will do
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@ -35,8 +35,9 @@ The struct :ref:`v4l2_audio <v4l2-audio>` returned by the
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The :ref:`VIDIOC_G_AUDIO <VIDIOC_G_AUDIO>` and
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:ref:`VIDIOC_G_AUDOUT <VIDIOC_G_AUDOUT>` ioctls report the current
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audio input and output, respectively. Note that, unlike
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:ref:`VIDIOC_G_INPUT <VIDIOC_G_INPUT>` and
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audio input and output, respectively.
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.. note:: Note that, unlike :ref:`VIDIOC_G_INPUT <VIDIOC_G_INPUT>` and
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:ref:`VIDIOC_G_OUTPUT <VIDIOC_G_OUTPUT>` these ioctls return a
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structure as :ref:`VIDIOC_ENUMAUDIO` and
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:ref:`VIDIOC_ENUMAUDOUT <VIDIOC_ENUMAUDOUT>` do, not just an index.
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@ -166,7 +166,7 @@ struct v4l2_buffer
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output device because the application did not pass new data in
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time.
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Note this may count the frames received e.g. over USB, without
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.. note:: This may count the frames received e.g. over USB, without
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taking into account the frames dropped by the remote hardware due
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to limited compression throughput or bus bandwidth. These devices
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identify by not enumerating any video standards, see
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@ -297,8 +297,10 @@ struct v4l2_plane
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stream, applications when it refers to an output stream. If the
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application sets this to 0 for an output stream, then
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``bytesused`` will be set to the size of the plane (see the
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``length`` field of this struct) by the driver. Note that the
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actual image data starts at ``data_offset`` which may not be 0.
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``length`` field of this struct) by the driver.
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.. note:: Note that the actual image data starts at ``data_offset``
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which may not be 0.
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- .. row 2
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@ -367,10 +369,11 @@ struct v4l2_plane
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-
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- Offset in bytes to video data in the plane. Drivers must set this
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field when ``type`` refers to a capture stream, applications when
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it refers to an output stream. Note that data_offset is included
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in ``bytesused``. So the size of the image in the plane is
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``bytesused``-``data_offset`` at offset ``data_offset`` from the
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start of the plane.
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it refers to an output stream.
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.. note:: That data_offset is included in ``bytesused``. So the
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size of the image in the plane is ``bytesused``-``data_offset``
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at offset ``data_offset`` from the start of the plane.
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- .. row 8
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@ -15,7 +15,7 @@ offset into a video signal.
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Applications can use the following API to select an area in the video
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signal, query the default area and the hardware limits.
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**NOTE**: Despite their name, the :ref:`VIDIOC_CROPCAP <VIDIOC_CROPCAP>`,
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.. note:: Despite their name, the :ref:`VIDIOC_CROPCAP <VIDIOC_CROPCAP>`,
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:ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` and :ref:`VIDIOC_S_CROP
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<VIDIOC_G_CROP>` ioctls apply to input as well as output devices.
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@ -38,9 +38,9 @@ support scaling or the :ref:`VIDIOC_G_CROP <VIDIOC_G_CROP>` and
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:ref:`VIDIOC_S_CROP <VIDIOC_G_CROP>` ioctls. Their size (and position
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where applicable) will be fixed in this case.
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**NOTE:** All capture and output devices must support the
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:ref:`VIDIOC_CROPCAP <VIDIOC_CROPCAP>` ioctl such that applications can
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determine if scaling takes place.
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.. note:: All capture and output devices must support the
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:ref:`VIDIOC_CROPCAP <VIDIOC_CROPCAP>` ioctl such that applications
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can determine if scaling takes place.
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Cropping Structures
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@ -144,7 +144,7 @@ reopening a device, such that piping data into or out of a device will
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work without special preparations. More advanced applications should
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ensure the parameters are suitable before starting I/O.
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**NOTE:** on the next two examples, a video capture device is assumed;
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.. note:: On the next two examples, a video capture device is assumed;
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change ``V4L2_BUF_TYPE_VIDEO_CAPTURE`` for other types of device.
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Example: Resetting the cropping parameters
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@ -207,7 +207,7 @@ Example: Simple downscaling
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Example: Selecting an output area
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=================================
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**NOTE:** This example assumes an output device.
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.. note:: This example assumes an output device.
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.. code-block:: c
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@ -246,7 +246,7 @@ Example: Selecting an output area
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Example: Current scaling factor and pixel aspect
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================================================
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**NOTE:** This example assumes a video capture device.
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.. note:: This example assumes a video capture device.
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.. code-block:: c
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@ -15,7 +15,9 @@ Conventionally V4L2 video capture devices are accessed through character
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device special files named ``/dev/video`` and ``/dev/video0`` to
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``/dev/video63`` with major number 81 and minor numbers 0 to 63.
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``/dev/video`` is typically a symbolic link to the preferred video
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device. Note the same device files are used for video output devices.
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device.
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.. note:: The same device file names are used for video output devices.
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Querying Capabilities
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@ -19,8 +19,10 @@ both sides and finally call :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`
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for both capture and output to start the codec.
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Video compression codecs use the MPEG controls to setup their codec
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parameters (note that the MPEG controls actually support many more
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codecs than just MPEG). See :ref:`mpeg-controls`.
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parameters
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.. note:: The MPEG controls actually support many more codecs than
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just MPEG. See :ref:`mpeg-controls`.
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Memory-to-memory devices can often be used as a shared resource: you can
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open the video node multiple times, each application setting up their
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@ -6,11 +6,10 @@
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Effect Devices Interface
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************************
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**Note**
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This interface has been be suspended from the V4L2 API implemented
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in Linux 2.6 until we have more experience with effect device
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interfaces.
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.. note::
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This interface has been be suspended from the V4L2 API.
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The implementation for such effects should be done
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via mem2mem devices.
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A V4L2 video effect device can do image effects, filtering, or combine
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two or more images or image streams. For example video transitions or
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@ -14,10 +14,11 @@ this interface, which borrows structures and ioctls of the
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:ref:`Video Overlay <overlay>` interface.
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The OSD function is accessible through the same character special file
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as the :ref:`Video Output <capture>` function. Note the default
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function of such a ``/dev/video`` device is video capturing or output.
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The OSD function is only available after calling the
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:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
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as the :ref:`Video Output <capture>` function.
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.. note:: The default function of such a ``/dev/video`` device is video
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capturing or output. The OSD function is only available after calling
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the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
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Querying Capabilities
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|
|
@ -14,7 +14,9 @@ Conventionally V4L2 video output devices are accessed through character
|
|||
device special files named ``/dev/video`` and ``/dev/video0`` to
|
||||
``/dev/video63`` with major number 81 and minor numbers 0 to 63.
|
||||
``/dev/video`` is typically a symbolic link to the preferred video
|
||||
device. Note the same device files are used for video capture devices.
|
||||
device.
|
||||
|
||||
..note:: The same device file names are used also for video capture devices.
|
||||
|
||||
|
||||
Querying Capabilities
|
||||
|
|
|
|||
|
|
@ -17,10 +17,11 @@ plants needed cooling towers this used to be the only way to put live
|
|||
video into a window.
|
||||
|
||||
Video overlay devices are accessed through the same character special
|
||||
files as :ref:`video capture <capture>` devices. Note the default
|
||||
function of a ``/dev/video`` device is video capturing. The overlay
|
||||
function is only available after calling the
|
||||
:ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
|
||||
files as :ref:`video capture <capture>` devices.
|
||||
|
||||
.. note:: The default function of a ``/dev/video`` device is video
|
||||
capturing. The overlay function is only available after calling
|
||||
the :ref:`VIDIOC_S_FMT <VIDIOC_G_FMT>` ioctl.
|
||||
|
||||
The driver may support simultaneous overlay and capturing using the
|
||||
read/write and streaming I/O methods. If so, operation at the nominal
|
||||
|
|
@ -235,8 +236,8 @@ exceeded are undefined. [3]_
|
|||
:ref:`VIDIOC_S_FBUF <VIDIOC_G_FBUF>`,
|
||||
:ref:`framebuffer-flags`).
|
||||
|
||||
**Note**: this field was added in Linux 2.6.23, extending the structure.
|
||||
However the :ref:`VIDIOC_[G|S|TRY]_FMT <VIDIOC_G_FMT>`
|
||||
.. note:: This field was added in Linux 2.6.23, extending the
|
||||
structure. However the :ref:`VIDIOC_[G|S|TRY]_FMT <VIDIOC_G_FMT>`
|
||||
ioctls, which take a pointer to a :ref:`v4l2_format <v4l2-format>`
|
||||
parent structure with padding bytes at the end, are not affected.
|
||||
|
||||
|
|
|
|||
|
|
@ -14,10 +14,10 @@ at devices capable of receiving and/or transmitting RDS information.
|
|||
For more information see the core RDS standard :ref:`iec62106` and the
|
||||
RBDS standard :ref:`nrsc4`.
|
||||
|
||||
Note that the RBDS standard as is used in the USA is almost identical to
|
||||
the RDS standard. Any RDS decoder/encoder can also handle RBDS. Only
|
||||
some of the fields have slightly different meanings. See the RBDS
|
||||
standard for more information.
|
||||
.. note:: Note that the RBDS standard as is used in the USA is almost
|
||||
identical to the RDS standard. Any RDS decoder/encoder can also handle
|
||||
RBDS. Only some of the fields have slightly different meanings. See the
|
||||
RBDS standard for more information.
|
||||
|
||||
The RBDS standard also specifies support for MMBS (Modified Mobile
|
||||
Search). This is a proprietary format which seems to be discontinued.
|
||||
|
|
|
|||
|
|
@ -72,14 +72,14 @@ reported on one (or several) V4L2 device nodes.
|
|||
Pad-level Formats
|
||||
=================
|
||||
|
||||
**Warning**
|
||||
.. warning::
|
||||
|
||||
Pad-level formats are only applicable to very complex device that
|
||||
Pad-level formats are only applicable to very complex devices that
|
||||
need to expose low-level format configuration to user space. Generic
|
||||
V4L2 applications do *not* need to use the API described in this
|
||||
section.
|
||||
|
||||
**Note**
|
||||
.. note::
|
||||
|
||||
For the purpose of this section, the term *format* means the
|
||||
combination of media bus data format, frame width and frame height.
|
||||
|
|
|
|||
|
|
@ -143,7 +143,10 @@ functions are always available.
|
|||
|
||||
To start and stop capturing or displaying applications call the
|
||||
:ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` and
|
||||
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` ioctls. Note that
|
||||
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` ioctls.
|
||||
|
||||
.. note::
|
||||
|
||||
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` removes all buffers from
|
||||
both queues and unlocks all buffers as a side effect. Since there is no
|
||||
notion of doing anything "now" on a multitasking system, if an
|
||||
|
|
|
|||
|
|
@ -84,13 +84,16 @@ themselves than is possible with
|
|||
particular, this ioctl gives the dimensions of the N-dimensional array
|
||||
if this control consists of more than one element.
|
||||
|
||||
It is important to realize that due to the flexibility of controls it is
|
||||
.. note::
|
||||
|
||||
#. It is important to realize that due to the flexibility of controls it is
|
||||
necessary to check whether the control you want to set actually is
|
||||
supported in the driver and what the valid range of values is. So use
|
||||
the :ref:`VIDIOC_QUERYCTRL` (or
|
||||
:ref:`VIDIOC_QUERY_EXT_CTRL <VIDIOC_QUERYCTRL>`) and
|
||||
:ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>` ioctls to check this. Also
|
||||
note that it is possible that some of the menu indices in a control of
|
||||
the :ref:`VIDIOC_QUERYCTRL` (or :ref:`VIDIOC_QUERY_EXT_CTRL
|
||||
<VIDIOC_QUERYCTRL>`) and :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`
|
||||
ioctls to check this.
|
||||
|
||||
#. It is possible that some of the menu indices in a control of
|
||||
type ``V4L2_CTRL_TYPE_MENU`` may not be supported (``VIDIOC_QUERYMENU``
|
||||
will return an error). A good example is the list of supported MPEG
|
||||
audio bitrates. Some drivers only support one or two bitrates, others
|
||||
|
|
@ -181,7 +184,7 @@ Codec Control Reference
|
|||
Below all controls within the Codec control class are described. First
|
||||
the generic controls, then controls specific for certain hardware.
|
||||
|
||||
Note: These controls are applicable to all codecs and not just MPEG. The
|
||||
.. note:: These controls are applicable to all codecs and not just MPEG. The
|
||||
defines are prefixed with V4L2_CID_MPEG/V4L2_MPEG as the controls
|
||||
were originally made for MPEG codecs and later extended to cover all
|
||||
encoding formats.
|
||||
|
|
@ -2282,12 +2285,14 @@ MFC 5.1 Control IDs
|
|||
``V4L2_CID_MPEG_MFC51_VIDEO_RC_REACTION_COEFF (integer)``
|
||||
Reaction coefficient for MFC rate control. Applicable to encoders.
|
||||
|
||||
Note 1: Valid only when the frame level RC is enabled.
|
||||
.. note::
|
||||
|
||||
Note 2: For tight CBR, this field must be small (ex. 2 ~ 10). For
|
||||
#. Valid only when the frame level RC is enabled.
|
||||
|
||||
#. For tight CBR, this field must be small (ex. 2 ~ 10). For
|
||||
VBR, this field must be large (ex. 100 ~ 1000).
|
||||
|
||||
Note 3: It is not recommended to use the greater number than
|
||||
#. It is not recommended to use the greater number than
|
||||
FRAME_RATE * (10^9 / BIT_RATE).
|
||||
|
||||
``V4L2_CID_MPEG_MFC51_VIDEO_H264_ADAPTIVE_RC_DARK (boolean)``
|
||||
|
|
@ -4107,6 +4112,8 @@ transmitters for `VGA <http://en.wikipedia.org/wiki/Vga>`__,
|
|||
the receiver or transmitter subdevice that implements them, so they are
|
||||
only exposed on the ``/dev/v4l-subdev*`` device node.
|
||||
|
||||
.. note::
|
||||
|
||||
Note that these devices can have multiple input or output pads which are
|
||||
hooked up to e.g. HDMI connectors. Even though the subdevice will
|
||||
receive or transmit video from/to only one of those pads, the other pads
|
||||
|
|
|
|||
|
|
@ -47,17 +47,20 @@ Arguments
|
|||
Regardless of the device type and the direction of data exchange it
|
||||
should be set to ``PROT_READ`` | ``PROT_WRITE``, permitting read
|
||||
and write access to image buffers. Drivers should support at least
|
||||
this combination of flags. Note the Linux ``video-buf`` kernel
|
||||
module, which is used by the bttv, saa7134, saa7146, cx88 and vivi
|
||||
driver supports only ``PROT_READ`` | ``PROT_WRITE``. When the
|
||||
driver does not support the desired protection the
|
||||
this combination of flags.
|
||||
|
||||
.. note::
|
||||
|
||||
#. The Linux ``videobuf`` kernel module, which is used by some
|
||||
drivers supports only ``PROT_READ`` | ``PROT_WRITE``. When the
|
||||
driver does not support the desired protection, the
|
||||
:ref:`mmap() <func-mmap>` function fails.
|
||||
|
||||
Note device memory accesses (e. g. the memory on a graphics card
|
||||
#. Device memory accesses (e. g. the memory on a graphics card
|
||||
with video capturing hardware) may incur a performance penalty
|
||||
compared to main memory accesses, or reads may be significantly
|
||||
slower than writes or vice versa. Other I/O methods may be more
|
||||
efficient in this case.
|
||||
efficient in such case.
|
||||
|
||||
``flags``
|
||||
The ``flags`` parameter specifies the type of the mapped object,
|
||||
|
|
@ -73,11 +76,13 @@ Arguments
|
|||
|
||||
One of the ``MAP_SHARED`` or ``MAP_PRIVATE`` flags must be set.
|
||||
``MAP_SHARED`` allows applications to share the mapped memory with
|
||||
other (e. g. child-) processes. Note the Linux ``video-buf`` module
|
||||
which is used by the bttv, saa7134, saa7146, cx88 and vivi driver
|
||||
supports only ``MAP_SHARED``. ``MAP_PRIVATE`` requests copy-on-write
|
||||
semantics. V4L2 applications should not set the ``MAP_PRIVATE``,
|
||||
``MAP_DENYWRITE``, ``MAP_EXECUTABLE`` or ``MAP_ANON`` flag.
|
||||
other (e. g. child-) processes.
|
||||
|
||||
.. note:: The Linux ``videobuf`` module which is used by some
|
||||
drivers supports only ``MAP_SHARED``. ``MAP_PRIVATE`` requests
|
||||
copy-on-write semantics. V4L2 applications should not set the
|
||||
``MAP_PRIVATE``, ``MAP_DENYWRITE``, ``MAP_EXECUTABLE`` or ``MAP_ANON``
|
||||
flags.
|
||||
|
||||
``fd``
|
||||
File descriptor returned by :ref:`open() <func-open>`.
|
||||
|
|
|
|||
|
|
@ -245,7 +245,9 @@ available. The :ref:`select() <func-select>` or :ref:`poll()
|
|||
|
||||
To start and stop capturing or output applications call the
|
||||
:ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` and :ref:`VIDIOC_STREAMOFF
|
||||
<VIDIOC_STREAMON>` ioctl. Note :ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
|
||||
<VIDIOC_STREAMON>` ioctl.
|
||||
|
||||
.. note:::ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
|
||||
removes all buffers from both queues as a side effect. Since there is
|
||||
no notion of doing anything "now" on a multitasking system, if an
|
||||
application needs to synchronize with another event it should examine
|
||||
|
|
|
|||
|
|
@ -17,9 +17,11 @@ identifier (enum :ref:`v4l2_quantization <v4l2-quantization>`) to
|
|||
specify non-standard quantization methods. Most of the time only the
|
||||
colorspace field of struct :ref:`v4l2_pix_format <v4l2-pix-format>`
|
||||
or struct :ref:`v4l2_pix_format_mplane <v4l2-pix-format-mplane>`
|
||||
needs to be filled in. Note that the default R'G'B' quantization is full
|
||||
range for all colorspaces except for BT.2020 which uses limited range
|
||||
R'G'B' quantization.
|
||||
needs to be filled in.
|
||||
|
||||
.. note:: The default R'G'B' quantization is full range for all
|
||||
colorspaces except for BT.2020 which uses limited range R'G'B'
|
||||
quantization.
|
||||
|
||||
|
||||
.. _v4l2-colorspace:
|
||||
|
|
|
|||
|
|
@ -536,7 +536,9 @@ Colorspace DCI-P3 (V4L2_COLORSPACE_DCI_P3)
|
|||
The :ref:`smpte431` standard defines the colorspace used by cinema
|
||||
projectors that use the DCI-P3 colorspace. The default transfer function
|
||||
is ``V4L2_XFER_FUNC_DCI_P3``. The default Y'CbCr encoding is
|
||||
``V4L2_YCBCR_ENC_709``. Note that this colorspace does not specify a
|
||||
``V4L2_YCBCR_ENC_709``.
|
||||
|
||||
.. note:: Note that this colorspace does not specify a
|
||||
Y'CbCr encoding since it is not meant to be encoded to Y'CbCr. So this
|
||||
default Y'CbCr encoding was picked because it is the HDTV encoding. The
|
||||
default Y'CbCr quantization is limited range. The chromaticities of the
|
||||
|
|
@ -752,7 +754,7 @@ reference are:
|
|||
- 0.316
|
||||
|
||||
|
||||
Note that this colorspace uses Illuminant C instead of D65 as the white
|
||||
.. note:: This colorspace uses Illuminant C instead of D65 as the white
|
||||
reference. To correctly convert an image in this colorspace to another
|
||||
that uses D65 you need to apply a chromatic adaptation algorithm such as
|
||||
the Bradford method.
|
||||
|
|
@ -886,7 +888,7 @@ reference are identical to sRGB. The transfer function use is
|
|||
with full range quantization where Y' is scaled to [0…255] and Cb/Cr are
|
||||
scaled to [-128…128] and then clipped to [-128…127].
|
||||
|
||||
Note that the JPEG standard does not actually store colorspace
|
||||
.. note:: The JPEG standard does not actually store colorspace
|
||||
information. So if something other than sRGB is used, then the driver
|
||||
will have to set that information explicitly. Effectively
|
||||
``V4L2_COLORSPACE_JPEG`` can be considered to be an abbreviation for
|
||||
|
|
|
|||
|
|
@ -17,9 +17,10 @@ Description
|
|||
This format is similar to
|
||||
:ref:`V4L2_PIX_FMT_SBGGR8 <V4L2-PIX-FMT-SBGGR8>`, except each pixel
|
||||
has a depth of 16 bits. The least significant byte is stored at lower
|
||||
memory addresses (little-endian). Note the actual sampling precision may
|
||||
be lower than 16 bits, for example 10 bits per pixel with values in
|
||||
range 0 to 1023.
|
||||
memory addresses (little-endian).
|
||||
|
||||
..note:: The actual sampling precision may be lower than 16 bits,
|
||||
for example 10 bits per pixel with values in tange 0 to 1023.
|
||||
|
||||
**Byte Order.**
|
||||
Each cell is one byte.
|
||||
|
|
|
|||
|
|
@ -15,9 +15,10 @@ Description
|
|||
===========
|
||||
|
||||
This is a grey-scale image with a depth of 16 bits per pixel. The most
|
||||
significant byte is stored at lower memory addresses (big-endian). Note
|
||||
the actual sampling precision may be lower than 16 bits, for example 10
|
||||
bits per pixel with values in range 0 to 1023.
|
||||
significant byte is stored at lower memory addresses (big-endian).
|
||||
|
||||
.. note:: Tthe actual sampling precision may be lower than 16 bits, for
|
||||
example 10 bits per pixel with values in range 0 to 1023.
|
||||
|
||||
**Byte Order.**
|
||||
Each cell is one byte.
|
||||
|
|
|
|||
|
|
@ -16,7 +16,8 @@ Description
|
|||
|
||||
This is a grey-scale image with a depth of 16 bits per pixel. The least
|
||||
significant byte is stored at lower memory addresses (little-endian).
|
||||
Note the actual sampling precision may be lower than 16 bits, for
|
||||
|
||||
.. note:: The actual sampling precision may be lower than 16 bits, for
|
||||
example 10 bits per pixel with values in range 0 to 1023.
|
||||
|
||||
**Byte Order.**
|
||||
|
|
|
|||
|
|
@ -39,8 +39,9 @@ To query and select the standard used by the current video input or
|
|||
output applications call the :ref:`VIDIOC_G_STD <VIDIOC_G_STD>` and
|
||||
:ref:`VIDIOC_S_STD <VIDIOC_G_STD>` ioctl, respectively. The
|
||||
*received* standard can be sensed with the
|
||||
:ref:`VIDIOC_QUERYSTD` ioctl. Note that the
|
||||
parameter of all these ioctls is a pointer to a
|
||||
:ref:`VIDIOC_QUERYSTD` ioctl.
|
||||
|
||||
..note:: The parameter of all these ioctls is a pointer to a
|
||||
:ref:`v4l2_std_id <v4l2-std-id>` type (a standard set), *not* an
|
||||
index into the standard enumeration. Drivers must implement all video
|
||||
standard ioctls when the device has one or more video inputs or outputs.
|
||||
|
|
|
|||
|
|
@ -26,13 +26,14 @@ To query and change tuner properties applications use the
|
|||
:ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` ioctls, respectively. The
|
||||
struct :ref:`v4l2_tuner <v4l2-tuner>` returned by :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>`
|
||||
also contains signal status information applicable when the tuner of the
|
||||
current video or radio input is queried. Note that :ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>`
|
||||
does not switch the current tuner, when there is more than one at all.
|
||||
The tuner is solely determined by the current video input. Drivers must
|
||||
support both ioctls and set the ``V4L2_CAP_TUNER`` flag in the struct
|
||||
:ref:`v4l2_capability <v4l2-capability>` returned by the
|
||||
:ref:`VIDIOC_QUERYCAP` ioctl when the device has
|
||||
one or more tuners.
|
||||
current video or radio input is queried.
|
||||
|
||||
.. note:: :ref:`VIDIOC_S_TUNER <VIDIOC_G_TUNER>` does not switch the
|
||||
current tuner, when there is more than one at all. The tuner is solely
|
||||
determined by the current video input. Drivers must support both ioctls
|
||||
and set the ``V4L2_CAP_TUNER`` flag in the struct :ref:`v4l2_capability
|
||||
<v4l2-capability>` returned by the :ref:`VIDIOC_QUERYCAP` ioctl when the
|
||||
device has one or more tuners.
|
||||
|
||||
|
||||
Modulators
|
||||
|
|
|
|||
|
|
@ -86,9 +86,10 @@ available.
|
|||
|
||||
To start and stop capturing or output applications call the
|
||||
:ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>` and
|
||||
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` ioctl. Note
|
||||
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` removes all buffers from both
|
||||
queues and unlocks all buffers as a side effect. Since there is no
|
||||
:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` ioctl.
|
||||
|
||||
.. note:: ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>` removes all buffers from
|
||||
both queues and unlocks all buffers as a side effect. Since there is no
|
||||
notion of doing anything "now" on a multitasking system, if an
|
||||
application needs to synchronize with another event it should examine
|
||||
the struct :ref:`v4l2_buffer <v4l2-buffer>` ``timestamp`` of captured or
|
||||
|
|
|
|||
|
|
@ -33,7 +33,7 @@ Arguments
|
|||
Description
|
||||
===========
|
||||
|
||||
**Note**
|
||||
.. note::
|
||||
|
||||
This is an :ref:`experimental` interface and may
|
||||
change in the future.
|
||||
|
|
|
|||
|
|
@ -35,7 +35,7 @@ Arguments
|
|||
Description
|
||||
===========
|
||||
|
||||
**Note**
|
||||
.. note::
|
||||
|
||||
This is an :ref:`experimental` interface and may
|
||||
change in the future.
|
||||
|
|
|
|||
|
|
@ -37,7 +37,9 @@ To query the capabilities of the DV receiver/transmitter applications
|
|||
initialize the ``pad`` field to 0, zero the reserved array of struct
|
||||
:ref:`v4l2_dv_timings_cap <v4l2-dv-timings-cap>` and call the
|
||||
``VIDIOC_DV_TIMINGS_CAP`` ioctl on a video node and the driver will fill
|
||||
in the structure. Note that drivers may return different values after
|
||||
in the structure.
|
||||
|
||||
.. note:: Drivers may return different values after
|
||||
switching the video input or output.
|
||||
|
||||
When implemented by the driver DV capabilities of subdevices can be
|
||||
|
|
|
|||
|
|
@ -47,8 +47,10 @@ field, set the ``pad`` field to 0, zero the reserved array of struct
|
|||
structure. Drivers fill the rest of the structure or return an ``EINVAL``
|
||||
error code when the index is out of bounds. To enumerate all supported
|
||||
DV timings, applications shall begin at index zero, incrementing by one
|
||||
until the driver returns ``EINVAL``. Note that drivers may enumerate a
|
||||
different set of DV timings after switching the video input or output.
|
||||
until the driver returns ``EINVAL``.
|
||||
|
||||
.. note:: Drivers may enumerate a different set of DV timings after
|
||||
switching the video input or output.
|
||||
|
||||
When implemented by the driver DV timings of subdevices can be queried
|
||||
by calling the ``VIDIOC_SUBDEV_ENUM_DV_TIMINGS`` ioctl directly on a
|
||||
|
|
|
|||
|
|
@ -40,7 +40,7 @@ fill the rest of the structure or return an ``EINVAL`` error code. All
|
|||
formats are enumerable by beginning at index zero and incrementing by
|
||||
one until ``EINVAL`` is returned.
|
||||
|
||||
Note that after switching input or output the list of enumerated image
|
||||
.. note:: After switching input or output the list of enumerated image
|
||||
formats may be different.
|
||||
|
||||
|
||||
|
|
@ -111,7 +111,9 @@ formats may be different.
|
|||
#define v4l2_fourcc(a,b,c,d) (((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24))
|
||||
|
||||
Several image formats are already defined by this specification in
|
||||
:ref:`pixfmt`. Note these codes are not the same as those used
|
||||
:ref:`pixfmt`.
|
||||
|
||||
.. attention:: These codes are not the same as those used
|
||||
in the Windows world.
|
||||
|
||||
- .. row 7
|
||||
|
|
|
|||
|
|
@ -73,7 +73,7 @@ the device supports. Only for the ``V4L2_FRMIVAL_TYPE_DISCRETE`` type
|
|||
does it make sense to increase the index value to receive more frame
|
||||
intervals.
|
||||
|
||||
Note that the order in which the frame intervals are returned has no
|
||||
.. note:: The order in which the frame intervals are returned has no
|
||||
special meaning. In particular does it not say anything about potential
|
||||
default frame intervals.
|
||||
|
||||
|
|
@ -82,16 +82,12 @@ without any interaction from the application itself. This means that the
|
|||
enumeration data is consistent if the application does not perform any
|
||||
other ioctl calls while it runs the frame interval enumeration.
|
||||
|
||||
.. note::
|
||||
|
||||
Notes
|
||||
=====
|
||||
|
||||
- **Frame intervals and frame rates:** The V4L2 API uses frame
|
||||
**Frame intervals and frame rates:** The V4L2 API uses frame
|
||||
intervals instead of frame rates. Given the frame interval the frame
|
||||
rate can be computed as follows:
|
||||
|
||||
|
||||
|
||||
::
|
||||
|
||||
frame_rate = 1 / frame_interval
|
||||
|
|
|
|||
|
|
@ -72,7 +72,7 @@ the ``type`` field to determine the type of frame size enumeration the
|
|||
device supports. Only for the ``V4L2_FRMSIZE_TYPE_DISCRETE`` type does
|
||||
it make sense to increase the index value to receive more frame sizes.
|
||||
|
||||
Note that the order in which the frame sizes are returned has no special
|
||||
.. note:: The order in which the frame sizes are returned has no special
|
||||
meaning. In particular does it not say anything about potential default
|
||||
format sizes.
|
||||
|
||||
|
|
|
|||
|
|
@ -127,12 +127,14 @@ of the corresponding tuner/modulator is set.
|
|||
- ``modulation``
|
||||
|
||||
- :cspan:`2` The supported modulation systems of this frequency
|
||||
band. See :ref:`band-modulation`. Note that currently only one
|
||||
modulation system per frequency band is supported. More work will
|
||||
need to be done if multiple modulation systems are possible.
|
||||
Contact the linux-media mailing list
|
||||
band. See :ref:`band-modulation`.
|
||||
|
||||
.. note:: Currently only one modulation system per frequency band
|
||||
is supported. More work will need to be done if multiple
|
||||
modulation systems are possible. Contact the linux-media
|
||||
mailing list
|
||||
(`https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__)
|
||||
if you need that functionality.
|
||||
if you need such functionality.
|
||||
|
||||
- .. row 8
|
||||
|
||||
|
|
|
|||
|
|
@ -41,8 +41,8 @@ structure or return an ``EINVAL`` error code when the index is out of
|
|||
bounds. To enumerate all audio outputs applications shall begin at index
|
||||
zero, incrementing by one until the driver returns ``EINVAL``.
|
||||
|
||||
Note connectors on a TV card to loop back the received audio signal to a
|
||||
sound card are not audio outputs in this sense.
|
||||
.. note:: Connectors on a TV card to loop back the received audio signal
|
||||
to a sound card are not audio outputs in this sense.
|
||||
|
||||
See :ref:`VIDIOC_G_AUDIOout <VIDIOC_G_AUDOUT>` for a description of struct
|
||||
:ref:`v4l2_audioout <v4l2-audioout>`.
|
||||
|
|
|
|||
|
|
@ -233,8 +233,8 @@ at index zero, incrementing by one until the driver returns ``EINVAL``.
|
|||
|
||||
- The input is connected to a device that produces a signal that is
|
||||
flipped vertically and does not correct this before passing the
|
||||
signal to userspace. Note that a 180 degree rotation is the same
|
||||
as HFLIP | VFLIP
|
||||
signal to userspace.
|
||||
.. note:: A 180 degree rotation is the same as HFLIP | VFLIP
|
||||
|
||||
- .. row 8
|
||||
|
||||
|
|
|
|||
|
|
@ -51,8 +51,8 @@ return the ``EINVAL`` error code when the index is out of bounds. This is a
|
|||
write-only ioctl, it does not return the current audio output attributes
|
||||
as ``VIDIOC_G_AUDOUT`` does.
|
||||
|
||||
Note connectors on a TV card to loop back the received audio signal to a
|
||||
sound card are not audio outputs in this sense.
|
||||
.. note:: Connectors on a TV card to loop back the received audio signal
|
||||
to a sound card are not audio outputs in this sense.
|
||||
|
||||
|
||||
.. _v4l2-audioout:
|
||||
|
|
|
|||
|
|
@ -65,7 +65,9 @@ If ``start_block`` and ``blocks`` are both set to 0 when
|
|||
:ref:`VIDIOC_G_EDID <VIDIOC_G_EDID>` is called, then the driver will set ``blocks`` to the
|
||||
total number of available EDID blocks and it will return 0 without
|
||||
copying any data. This is an easy way to discover how many EDID blocks
|
||||
there are. Note that if there are no EDID blocks available at all, then
|
||||
there are.
|
||||
|
||||
.. note:: If there are no EDID blocks available at all, then
|
||||
the driver will set ``blocks`` to 0 and it returns 0.
|
||||
|
||||
To set the EDID blocks of a receiver the application has to fill in the
|
||||
|
|
|
|||
|
|
@ -125,7 +125,9 @@ still cause this situation.
|
|||
the payload. If :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` finds that this value is
|
||||
less than is required to store the payload result, then it is set
|
||||
to a value large enough to store the payload result and ``ENOSPC`` is
|
||||
returned. Note that for string controls this ``size`` field should
|
||||
returned.
|
||||
|
||||
.. note:: For string controls, this ``size`` field should
|
||||
not be confused with the length of the string. This field refers
|
||||
to the size of the memory that contains the string. The actual
|
||||
*length* of the string may well be much smaller.
|
||||
|
|
@ -261,8 +263,10 @@ still cause this situation.
|
|||
- Which value of the control to get/set/try.
|
||||
``V4L2_CTRL_WHICH_CUR_VAL`` will return the current value of the
|
||||
control and ``V4L2_CTRL_WHICH_DEF_VAL`` will return the default
|
||||
value of the control. Please note that you can only get the
|
||||
default value of the control, you cannot set or try it.
|
||||
value of the control.
|
||||
|
||||
.. note:: You can only get the default value of the control,
|
||||
you cannot set or try it.
|
||||
|
||||
For backwards compatibility you can also use a control class here
|
||||
(see :ref:`ctrl-class`). In that case all controls have to
|
||||
|
|
|
|||
|
|
@ -128,12 +128,14 @@ To change the radio frequency the
|
|||
|
||||
- With this field applications can determine how audio sub-carriers
|
||||
shall be modulated. It contains a set of flags as defined in
|
||||
:ref:`modulator-txsubchans`. Note the tuner ``rxsubchans`` flags
|
||||
are reused, but the semantics are different. Video output devices
|
||||
:ref:`modulator-txsubchans`.
|
||||
|
||||
.. note:: The tuner ``rxsubchans`` flags are reused, but the
|
||||
semantics are different. Video output devices
|
||||
are assumed to have an analog or PCM audio input with 1-3
|
||||
channels. The ``txsubchans`` flags select one or more channels for
|
||||
modulation, together with some audio subprogram indicator, for
|
||||
example a stereo pilot tone.
|
||||
channels. The ``txsubchans`` flags select one or more channels
|
||||
for modulation, together with some audio subprogram indicator,
|
||||
for example, a stereo pilot tone.
|
||||
|
||||
- .. row 7
|
||||
|
||||
|
|
|
|||
|
|
@ -40,7 +40,7 @@ output device, applications initialize the ``type`` field of a struct
|
|||
driver fills in the remaining fields or returns an ``EINVAL`` error code if
|
||||
the sliced VBI API is unsupported or ``type`` is invalid.
|
||||
|
||||
Note the ``type`` field was added, and the ioctl changed from read-only
|
||||
.. note:: The ``type`` field was added, and the ioctl changed from read-only
|
||||
to write-read, in Linux 2.6.19.
|
||||
|
||||
|
||||
|
|
|
|||
|
|
@ -391,8 +391,8 @@ To change the radio frequency the
|
|||
carrier for a monaural secondary language. Only
|
||||
``V4L2_TUNER_ANALOG_TV`` tuners can have this capability.
|
||||
|
||||
Note the ``V4L2_TUNER_CAP_LANG2`` and ``V4L2_TUNER_CAP_SAP`` flags
|
||||
are synonyms. ``V4L2_TUNER_CAP_SAP`` applies when the tuner
|
||||
.. note:: The ``V4L2_TUNER_CAP_LANG2`` and ``V4L2_TUNER_CAP_SAP``
|
||||
flags are synonyms. ``V4L2_TUNER_CAP_SAP`` applies when the tuner
|
||||
supports the ``V4L2_STD_NTSC_M`` video standard.
|
||||
|
||||
- .. row 9
|
||||
|
|
@ -500,10 +500,11 @@ To change the radio frequency the
|
|||
|
||||
- 0x0004
|
||||
|
||||
- The tuner receives a Second Audio Program. Note the
|
||||
``V4L2_TUNER_SUB_LANG2`` and ``V4L2_TUNER_SUB_SAP`` flags are
|
||||
synonyms. The ``V4L2_TUNER_SUB_SAP`` flag applies when the current
|
||||
video standard is ``V4L2_STD_NTSC_M``.
|
||||
- The tuner receives a Second Audio Program.
|
||||
|
||||
.. note:: The ``V4L2_TUNER_SUB_LANG2`` and ``V4L2_TUNER_SUB_SAP``
|
||||
flags are synonyms. The ``V4L2_TUNER_SUB_SAP`` flag applies
|
||||
when the current video standard is ``V4L2_STD_NTSC_M``.
|
||||
|
||||
- .. row 6
|
||||
|
||||
|
|
@ -578,9 +579,10 @@ To change the radio frequency the
|
|||
- Play the Second Audio Program. When the tuner receives no
|
||||
bilingual audio or SAP, or their reception is not supported the
|
||||
driver shall fall back to mono or stereo mode. Only
|
||||
``V4L2_TUNER_ANALOG_TV`` tuners support this mode. Note the
|
||||
``V4L2_TUNER_MODE_LANG2`` and ``V4L2_TUNER_MODE_SAP`` are
|
||||
synonyms.
|
||||
``V4L2_TUNER_ANALOG_TV`` tuners support this mode.
|
||||
|
||||
.. note:: The ``V4L2_TUNER_MODE_LANG2`` and ``V4L2_TUNER_MODE_SAP``
|
||||
are synonyms.
|
||||
|
||||
- .. row 6
|
||||
|
||||
|
|
|
|||
|
|
@ -135,12 +135,13 @@ EINVAL
|
|||
|
||||
EIO
|
||||
``VIDIOC_DQBUF`` failed due to an internal error. Can also indicate
|
||||
temporary problems like signal loss. Note the driver might dequeue
|
||||
an (empty) buffer despite returning an error, or even stop
|
||||
capturing. Reusing such buffer may be unsafe though and its details
|
||||
(e.g. ``index``) may not be returned either. It is recommended that
|
||||
drivers indicate recoverable errors by setting the
|
||||
``V4L2_BUF_FLAG_ERROR`` and returning 0 instead. In that case the
|
||||
temporary problems like signal loss.
|
||||
|
||||
.. note:: The driver might dequeue an (empty) buffer despite returning
|
||||
an error, or even stop capturing. Reusing such buffer may be unsafe
|
||||
though and its details (e.g. ``index``) may not be returned either.
|
||||
It is recommended that drivers indicate recoverable errors by setting
|
||||
the ``V4L2_BUF_FLAG_ERROR`` and returning 0 instead. In that case the
|
||||
application should be able to safely reuse the buffer and continue
|
||||
streaming.
|
||||
|
||||
|
|
|
|||
|
|
@ -39,7 +39,7 @@ similar to sensing the video standard. To do so, applications call
|
|||
:ref:`v4l2_dv_timings <v4l2-dv-timings>`. Once the hardware detects
|
||||
the timings, it will fill in the timings structure.
|
||||
|
||||
Please note that drivers shall *not* switch timings automatically if new
|
||||
.. note:: Drivers shall *not* switch timings automatically if new
|
||||
timings are detected. Instead, drivers should send the
|
||||
``V4L2_EVENT_SOURCE_CHANGE`` event (if they support this) and expect
|
||||
that userspace will take action by calling :ref:`VIDIOC_QUERY_DV_TIMINGS`.
|
||||
|
|
|
|||
|
|
@ -82,7 +82,9 @@ fills the rest of the structure or returns an ``EINVAL`` error code when the
|
|||
``id`` or ``index`` is invalid. Menu items are enumerated by calling
|
||||
``VIDIOC_QUERYMENU`` with successive ``index`` values from struct
|
||||
:ref:`v4l2_queryctrl <v4l2-queryctrl>` ``minimum`` to ``maximum``,
|
||||
inclusive. Note that it is possible for ``VIDIOC_QUERYMENU`` to return
|
||||
inclusive.
|
||||
|
||||
.. note:: It is possible for ``VIDIOC_QUERYMENU`` to return
|
||||
an ``EINVAL`` error code for some indices between ``minimum`` and
|
||||
``maximum``. In that case that particular menu item is not supported by
|
||||
this driver. Also note that the ``minimum`` value is not necessarily 0.
|
||||
|
|
@ -184,9 +186,10 @@ See also the examples in :ref:`control`.
|
|||
|
||||
- The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_BOOLEAN``,
|
||||
``_BITMASK``, ``_MENU`` or ``_INTEGER_MENU`` control. Not valid
|
||||
for other types of controls. Note that drivers reset controls to
|
||||
their default value only when the driver is first loaded, never
|
||||
afterwards.
|
||||
for other types of controls.
|
||||
|
||||
.. note:: Drivers reset controls to their default value only when
|
||||
the driver is first loaded, never afterwards.
|
||||
|
||||
- .. row 8
|
||||
|
||||
|
|
@ -301,9 +304,10 @@ See also the examples in :ref:`control`.
|
|||
|
||||
- The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``,
|
||||
``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8``
|
||||
or ``_U16`` control. Not valid for other types of controls. Note
|
||||
that drivers reset controls to their default value only when the
|
||||
driver is first loaded, never afterwards.
|
||||
or ``_U16`` control. Not valid for other types of controls.
|
||||
|
||||
.. note:: Drivers reset controls to their default value only when
|
||||
the driver is first loaded, never afterwards.
|
||||
|
||||
- .. row 8
|
||||
|
||||
|
|
@ -722,11 +726,12 @@ See also the examples in :ref:`control`.
|
|||
control changes continuously. A typical example would be the
|
||||
current gain value if the device is in auto-gain mode. In such a
|
||||
case the hardware calculates the gain value based on the lighting
|
||||
conditions which can change over time. Note that setting a new
|
||||
value for a volatile control will have no effect and no
|
||||
``V4L2_EVENT_CTRL_CH_VALUE`` will be sent, unless the
|
||||
``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` flag (see below) is also set.
|
||||
Otherwise the new value will just be ignored.
|
||||
conditions which can change over time.
|
||||
|
||||
.. note:: Setting a new value for a volatile control will have no
|
||||
effect and no ``V4L2_EVENT_CTRL_CH_VALUE`` will be sent, unless
|
||||
the ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` flag (see below) is
|
||||
also set. Otherwise the new value will just be ignored.
|
||||
|
||||
- .. row 9
|
||||
|
||||
|
|
|
|||
|
|
@ -43,7 +43,7 @@ will return V4L2_STD_UNKNOWN. When detection is not possible or fails,
|
|||
the set must contain all standards supported by the current video input
|
||||
or output.
|
||||
|
||||
Please note that drivers shall *not* switch the video standard
|
||||
.. note:: Drivers shall *not* switch the video standard
|
||||
automatically if a new video standard is detected. Instead, drivers
|
||||
should send the ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support
|
||||
this) and expect that userspace will take action by calling
|
||||
|
|
|
|||
|
|
@ -76,7 +76,7 @@ then 0 is returned. Nothing happens in the case of ``VIDIOC_STREAMON``,
|
|||
but ``VIDIOC_STREAMOFF`` will return queued buffers to their starting
|
||||
state as mentioned above.
|
||||
|
||||
Note that applications can be preempted for unknown periods right before
|
||||
.. note:: Applications can be preempted for unknown periods right before
|
||||
or after the ``VIDIOC_STREAMON`` or ``VIDIOC_STREAMOFF`` calls, there is
|
||||
no notion of starting or stopping "now". Buffer timestamps can be used
|
||||
to synchronize with other events.
|
||||
|
|
|
|||
|
|
@ -35,7 +35,7 @@ Arguments
|
|||
Description
|
||||
===========
|
||||
|
||||
**Note**
|
||||
.. note::
|
||||
|
||||
This is an :ref:`obsolete` interface and may be removed
|
||||
in the future. It is superseded by
|
||||
|
|
|
|||
|
|
@ -51,9 +51,11 @@ using the :ref:`VIDIOC_DQEVENT` ioctl.
|
|||
|
||||
- ``type``
|
||||
|
||||
- Type of the event, see :ref:`event-type`. Note that
|
||||
``V4L2_EVENT_ALL`` can be used with VIDIOC_UNSUBSCRIBE_EVENT for
|
||||
unsubscribing all events at once.
|
||||
- Type of the event, see :ref:`event-type`.
|
||||
|
||||
.. note:: ``V4L2_EVENT_ALL`` can be used with
|
||||
:ref:`VIDIOC_UNSUBSCRIBE_EVENT` for unsubscribing all events
|
||||
at once.
|
||||
|
||||
- .. row 2
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue