![Mauro Carvalho Chehab](/assets/img/avatar_default.png)
The V4L and DVB API's are there for a long time. however, up to now, no efforts were done to merge them to kernel DocBook. This patch adds the current versions of the specs as an unique compendium. Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
202 lines
6.7 KiB
XML
202 lines
6.7 KiB
XML
<refentry id="vidioc-g-fmt">
|
|
<refmeta>
|
|
<refentrytitle>ioctl VIDIOC_G_FMT, VIDIOC_S_FMT,
|
|
VIDIOC_TRY_FMT</refentrytitle>
|
|
&manvol;
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>VIDIOC_G_FMT</refname>
|
|
<refname>VIDIOC_S_FMT</refname>
|
|
<refname>VIDIOC_TRY_FMT</refname>
|
|
<refpurpose>Get or set the data format, try a format</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<funcsynopsis>
|
|
<funcprototype>
|
|
<funcdef>int <function>ioctl</function></funcdef>
|
|
<paramdef>int <parameter>fd</parameter></paramdef>
|
|
<paramdef>int <parameter>request</parameter></paramdef>
|
|
<paramdef>struct v4l2_format
|
|
*<parameter>argp</parameter></paramdef>
|
|
</funcprototype>
|
|
</funcsynopsis>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Arguments</title>
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><parameter>fd</parameter></term>
|
|
<listitem>
|
|
<para>&fd;</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><parameter>request</parameter></term>
|
|
<listitem>
|
|
<para>VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><parameter>argp</parameter></term>
|
|
<listitem>
|
|
<para></para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para>These ioctls are used to negotiate the format of data
|
|
(typically image format) exchanged between driver and
|
|
application.</para>
|
|
|
|
<para>To query the current parameters applications set the
|
|
<structfield>type</structfield> field of a struct
|
|
<structname>v4l2_format</structname> to the respective buffer (stream)
|
|
type. For example video capture devices use
|
|
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>. When the application
|
|
calls the <constant>VIDIOC_G_FMT</constant> ioctl with a pointer to
|
|
this structure the driver fills the respective member of the
|
|
<structfield>fmt</structfield> union. In case of video capture devices
|
|
that is the &v4l2-pix-format; <structfield>pix</structfield> member.
|
|
When the requested buffer type is not supported drivers return an
|
|
&EINVAL;.</para>
|
|
|
|
<para>To change the current format parameters applications
|
|
initialize the <structfield>type</structfield> field and all
|
|
fields of the respective <structfield>fmt</structfield>
|
|
union member. For details see the documentation of the various devices
|
|
types in <xref linkend="devices" />. Good practice is to query the
|
|
current parameters first, and to
|
|
modify only those parameters not suitable for the application. When
|
|
the application calls the <constant>VIDIOC_S_FMT</constant> ioctl
|
|
with a pointer to a <structname>v4l2_format</structname> structure
|
|
the driver checks
|
|
and adjusts the parameters against hardware abilities. Drivers
|
|
should not return an error code unless the input is ambiguous, this is
|
|
a mechanism to fathom device capabilities and to approach parameters
|
|
acceptable for both the application and driver. On success the driver
|
|
may program the hardware, allocate resources and generally prepare for
|
|
data exchange.
|
|
Finally the <constant>VIDIOC_S_FMT</constant> ioctl returns the
|
|
current format parameters as <constant>VIDIOC_G_FMT</constant> does.
|
|
Very simple, inflexible devices may even ignore all input and always
|
|
return the default parameters. However all V4L2 devices exchanging
|
|
data with the application must implement the
|
|
<constant>VIDIOC_G_FMT</constant> and
|
|
<constant>VIDIOC_S_FMT</constant> ioctl. When the requested buffer
|
|
type is not supported drivers return an &EINVAL; on a
|
|
<constant>VIDIOC_S_FMT</constant> attempt. When I/O is already in
|
|
progress or the resource is not available for other reasons drivers
|
|
return the &EBUSY;.</para>
|
|
|
|
<para>The <constant>VIDIOC_TRY_FMT</constant> ioctl is equivalent
|
|
to <constant>VIDIOC_S_FMT</constant> with one exception: it does not
|
|
change driver state. It can also be called at any time, never
|
|
returning <errorcode>EBUSY</errorcode>. This function is provided to
|
|
negotiate parameters, to learn about hardware limitations, without
|
|
disabling I/O or possibly time consuming hardware preparations.
|
|
Although strongly recommended drivers are not required to implement
|
|
this ioctl.</para>
|
|
|
|
<table pgwide="1" frame="none" id="v4l2-format">
|
|
<title>struct <structname>v4l2_format</structname></title>
|
|
<tgroup cols="4">
|
|
<colspec colname="c1" />
|
|
<colspec colname="c2" />
|
|
<colspec colname="c3" />
|
|
<colspec colname="c4" />
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry>&v4l2-buf-type;</entry>
|
|
<entry><structfield>type</structfield></entry>
|
|
<entry></entry>
|
|
<entry>Type of the data stream, see <xref
|
|
linkend="v4l2-buf-type" />.</entry>
|
|
</row>
|
|
<row>
|
|
<entry>union</entry>
|
|
<entry><structfield>fmt</structfield></entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry>&v4l2-pix-format;</entry>
|
|
<entry><structfield>pix</structfield></entry>
|
|
<entry>Definition of an image format, see <xref
|
|
linkend="pixfmt" />, used by video capture and output
|
|
devices.</entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry>&v4l2-window;</entry>
|
|
<entry><structfield>win</structfield></entry>
|
|
<entry>Definition of an overlaid image, see <xref
|
|
linkend="overlay" />, used by video overlay devices.</entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry>&v4l2-vbi-format;</entry>
|
|
<entry><structfield>vbi</structfield></entry>
|
|
<entry>Raw VBI capture or output parameters. This is
|
|
discussed in more detail in <xref linkend="raw-vbi" />. Used by raw VBI
|
|
capture and output devices.</entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry>&v4l2-sliced-vbi-format;</entry>
|
|
<entry><structfield>sliced</structfield></entry>
|
|
<entry>Sliced VBI capture or output parameters. See
|
|
<xref linkend="sliced" /> for details. Used by sliced VBI
|
|
capture and output devices.</entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry>__u8</entry>
|
|
<entry><structfield>raw_data</structfield>[200]</entry>
|
|
<entry>Place holder for future extensions and custom
|
|
(driver defined) formats with <structfield>type</structfield>
|
|
<constant>V4L2_BUF_TYPE_PRIVATE</constant> and higher.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
&return-value;
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><errorcode>EBUSY</errorcode></term>
|
|
<listitem>
|
|
<para>The data format cannot be changed at this
|
|
time, for example because I/O is already in progress.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><errorcode>EINVAL</errorcode></term>
|
|
<listitem>
|
|
<para>The &v4l2-format; <structfield>type</structfield>
|
|
field is invalid, the requested buffer type not supported, or
|
|
<constant>VIDIOC_TRY_FMT</constant> was called and is not
|
|
supported with this buffer type.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect1>
|
|
</refentry>
|
|
|
|
<!--
|
|
Local Variables:
|
|
mode: sgml
|
|
sgml-parent-document: "v4l2.sgml"
|
|
indent-tabs-mode: nil
|
|
End:
|
|
-->
|