331 lines
12 KiB
XML
331 lines
12 KiB
XML
<refentry id="vidioc-querycap">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_QUERYCAP</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_QUERYCAP</refname>
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<refpurpose>Query device capabilities</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_capability *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_QUERYCAP</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>All V4L2 devices support the
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<constant>VIDIOC_QUERYCAP</constant> ioctl. It is used to identify
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kernel devices compatible with this specification and to obtain
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information about driver and hardware capabilities. The ioctl takes a
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pointer to a &v4l2-capability; which is filled by the driver. When the
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driver is not compatible with this specification the ioctl returns an
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&EINVAL;.</para>
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<table pgwide="1" frame="none" id="v4l2-capability">
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<title>struct <structname>v4l2_capability</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u8</entry>
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<entry><structfield>driver</structfield>[16]</entry>
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<entry><para>Name of the driver, a unique NUL-terminated
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ASCII string. For example: "bttv". Driver specific applications can
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use this information to verify the driver identity. It is also useful
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to work around known bugs, or to identify drivers in error reports.</para>
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<para>Storing strings in fixed sized arrays is bad
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practice but unavoidable here. Drivers and applications should take
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precautions to never read or write beyond the end of the array and to
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make sure the strings are properly NUL-terminated.</para></entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>card</structfield>[32]</entry>
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<entry>Name of the device, a NUL-terminated ASCII string.
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For example: "Yoyodyne TV/FM". One driver may support different brands
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or models of video hardware. This information is intended for users,
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for example in a menu of available devices. Since multiple TV cards of
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the same brand may be installed which are supported by the same
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driver, this name should be combined with the character device file
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name (⪚ <filename>/dev/video2</filename>) or the
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<structfield>bus_info</structfield> string to avoid
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ambiguities.</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>bus_info</structfield>[32]</entry>
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<entry>Location of the device in the system, a
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NUL-terminated ASCII string. For example: "PCI Slot 4". This
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information is intended for users, to distinguish multiple
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identical devices. If no such information is available the field may
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simply count the devices controlled by the driver, or contain the
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empty string (<structfield>bus_info</structfield>[0] = 0).<!-- XXX pci_dev->slot_name example --></entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>version</structfield></entry>
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<entry><para>Version number of the driver.</para>
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<para>Starting on kernel 3.1, the version reported is provided per
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V4L2 subsystem, following the same Kernel numberation scheme. However, it
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should not always return the same version as the kernel, if, for example,
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an stable or distribution-modified kernel uses the V4L2 stack from a
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newer kernel.</para>
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<para>The version number is formatted using the
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<constant>KERNEL_VERSION()</constant> macro:</para></entry>
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</row>
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<row>
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<entry spanname="hspan"><para>
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<programlisting>
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#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))
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__u32 version = KERNEL_VERSION(0, 8, 1);
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printf ("Version: %u.%u.%u\n",
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(version >> 16) & 0xFF,
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(version >> 8) & 0xFF,
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version & 0xFF);
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</programlisting></para></entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>capabilities</structfield></entry>
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<entry>Available capabilities of the physical device as a whole, see <xref
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linkend="device-capabilities" />. The same physical device can export
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multiple devices in /dev (e.g. /dev/videoX, /dev/vbiY and /dev/radioZ).
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The <structfield>capabilities</structfield> field should contain a union
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of all capabilities available around the several V4L2 devices exported
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to userspace.
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For all those devices the <structfield>capabilities</structfield> field
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returns the same set of capabilities. This allows applications to open
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just one of the devices (typically the video device) and discover whether
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video, vbi and/or radio are also supported.
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</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>device_caps</structfield></entry>
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<entry>Device capabilities of the opened device, see <xref
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linkend="device-capabilities" />. Should contain the available capabilities
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of that specific device node. So, for example, <structfield>device_caps</structfield>
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of a radio device will only contain radio related capabilities and
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no video or vbi capabilities. This field is only set if the <structfield>capabilities</structfield>
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field contains the <constant>V4L2_CAP_DEVICE_CAPS</constant> capability.
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Only the <structfield>capabilities</structfield> field can have the
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<constant>V4L2_CAP_DEVICE_CAPS</constant> capability, <structfield>device_caps</structfield>
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will never set <constant>V4L2_CAP_DEVICE_CAPS</constant>.
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</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[3]</entry>
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<entry>Reserved for future extensions. Drivers must set
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this array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="device-capabilities">
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<title>Device Capabilities Flags</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_CAP_VIDEO_CAPTURE</constant></entry>
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<entry>0x00000001</entry>
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<entry>The device supports the single-planar API through the <link
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linkend="capture">Video Capture</link> interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VIDEO_CAPTURE_MPLANE</constant></entry>
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<entry>0x00001000</entry>
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<entry>The device supports the
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<link linkend="planar-apis">multi-planar API</link> through the
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<link linkend="capture">Video Capture</link> interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VIDEO_OUTPUT</constant></entry>
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<entry>0x00000002</entry>
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<entry>The device supports the single-planar API through the <link
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linkend="output">Video Output</link> interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VIDEO_OUTPUT_MPLANE</constant></entry>
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<entry>0x00002000</entry>
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<entry>The device supports the
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<link linkend="planar-apis">multi-planar API</link> through the
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<link linkend="output">Video Output</link> interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VIDEO_M2M</constant></entry>
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<entry>0x00004000</entry>
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<entry>The device supports the single-planar API through the
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Video Memory-To-Memory interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VIDEO_M2M_MPLANE</constant></entry>
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<entry>0x00008000</entry>
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<entry>The device supports the
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<link linkend="planar-apis">multi-planar API</link> through the
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Video Memory-To-Memory interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VIDEO_OVERLAY</constant></entry>
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<entry>0x00000004</entry>
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<entry>The device supports the <link
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linkend="overlay">Video Overlay</link> interface. A video overlay device
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typically stores captured images directly in the video memory of a
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graphics card, with hardware clipping and scaling.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VBI_CAPTURE</constant></entry>
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<entry>0x00000010</entry>
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<entry>The device supports the <link linkend="raw-vbi">Raw
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VBI Capture</link> interface, providing Teletext and Closed Caption
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data.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VBI_OUTPUT</constant></entry>
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<entry>0x00000020</entry>
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<entry>The device supports the <link linkend="raw-vbi">Raw VBI Output</link> interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_SLICED_VBI_CAPTURE</constant></entry>
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<entry>0x00000040</entry>
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<entry>The device supports the <link linkend="sliced">Sliced VBI Capture</link> interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_SLICED_VBI_OUTPUT</constant></entry>
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<entry>0x00000080</entry>
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<entry>The device supports the <link linkend="sliced">Sliced VBI Output</link> interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_RDS_CAPTURE</constant></entry>
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<entry>0x00000100</entry>
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<entry>The device supports the <link linkend="rds">RDS</link> capture interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_VIDEO_OUTPUT_OVERLAY</constant></entry>
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<entry>0x00000200</entry>
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<entry>The device supports the <link linkend="osd">Video
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Output Overlay</link> (OSD) interface. Unlike the <wordasword>Video
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Overlay</wordasword> interface, this is a secondary function of video
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output devices and overlays an image onto an outgoing video signal.
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When the driver sets this flag, it must clear the
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<constant>V4L2_CAP_VIDEO_OVERLAY</constant> flag and vice
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versa.<footnote><para>The &v4l2-framebuffer; lacks an
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&v4l2-buf-type; field, therefore the type of overlay is implied by the
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driver capabilities.</para></footnote></entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_HW_FREQ_SEEK</constant></entry>
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<entry>0x00000400</entry>
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<entry>The device supports the &VIDIOC-S-HW-FREQ-SEEK; ioctl for
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hardware frequency seeking.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_RDS_OUTPUT</constant></entry>
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<entry>0x00000800</entry>
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<entry>The device supports the <link linkend="rds">RDS</link> output interface.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_TUNER</constant></entry>
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<entry>0x00010000</entry>
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<entry>The device has some sort of tuner to
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receive RF-modulated video signals. For more information about
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tuner programming see
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<xref linkend="tuner" />.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_AUDIO</constant></entry>
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<entry>0x00020000</entry>
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<entry>The device has audio inputs or outputs. It may or
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may not support audio recording or playback, in PCM or compressed
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formats. PCM audio support must be implemented as ALSA or OSS
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interface. For more information on audio inputs and outputs see <xref
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linkend="audio" />.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_RADIO</constant></entry>
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<entry>0x00040000</entry>
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<entry>This is a radio receiver.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_MODULATOR</constant></entry>
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<entry>0x00080000</entry>
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<entry>The device has some sort of modulator to
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emit RF-modulated video/audio signals. For more information about
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modulator programming see
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<xref linkend="tuner" />.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_READWRITE</constant></entry>
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<entry>0x01000000</entry>
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<entry>The device supports the <link
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linkend="rw">read()</link> and/or <link linkend="rw">write()</link>
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I/O methods.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_ASYNCIO</constant></entry>
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<entry>0x02000000</entry>
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<entry>The device supports the <link
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linkend="async">asynchronous</link> I/O methods.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_STREAMING</constant></entry>
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<entry>0x04000000</entry>
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<entry>The device supports the <link
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linkend="mmap">streaming</link> I/O method.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CAP_DEVICE_CAPS</constant></entry>
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<entry>0x80000000</entry>
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<entry>The driver fills the <structfield>device_caps</structfield>
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field. This capability can only appear in the <structfield>capabilities</structfield>
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field and never in the <structfield>device_caps</structfield> field.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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</refsect1>
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</refentry>
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