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A driver might detect a new standard or DV timings, but it will never change to those new timings automatically. Instead it will send an event and let the application take care of it. Make this explicit in the documentation. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
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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