86 lines
2.7 KiB
XML
86 lines
2.7 KiB
XML
<refentry id="vidioc-querystd">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_QUERYSTD</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_QUERYSTD</refname>
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<refpurpose>Sense the video standard received by the current
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input</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>v4l2_std_id *<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_QUERYSTD</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>The hardware may be able to detect the current video
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standard automatically. To do so, applications call <constant>
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VIDIOC_QUERYSTD</constant> with a pointer to a &v4l2-std-id; type. The
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driver stores here a set of candidates, this can be a single flag or a
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set of supported standards if for example the hardware can only
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distinguish between 50 and 60 Hz systems. If no signal was detected,
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then the driver will return V4L2_STD_UNKNOWN. When detection is not
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possible or fails, the set must contain all standards supported by the
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current video input or output.</para>
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<para>Please note that drivers shall <emphasis>not</emphasis> switch the video standard
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automatically if a new video standard is detected. Instead, drivers should send the
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<constant>V4L2_EVENT_SOURCE_CHANGE</constant> event (if they support this) and expect
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that userspace will take action by calling <constant>VIDIOC_QUERYSTD</constant>.
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The reason is that a new video standard can mean different buffer sizes as well, and you
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cannot change buffer sizes on the fly. In general, applications that receive the
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Source Change event will have to call <constant>VIDIOC_QUERYSTD</constant>,
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and if the detected video standard is valid they will have to stop streaming, set the new
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standard, allocate new buffers and start streaming again.</para>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>ENODATA</errorcode></term>
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<listitem>
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<para>Standard video timings are not supported for this input or output.</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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</refentry>
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