CooCenter-System-kernel/Documentation/DocBook/media/v4l/vidioc-enum-fmt.xml

<refentry id="vidioc-enum-fmt">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_ENUM_FMT</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_ENUM_FMT</refname>
    <refpurpose>Enumerate image formats</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_fmtdesc
*<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_ENUM_FMT</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>To enumerate image formats applications initialize the
<structfield>type</structfield> and <structfield>index</structfield>
field of &v4l2-fmtdesc; and call the
<constant>VIDIOC_ENUM_FMT</constant> ioctl with a pointer to this
structure. Drivers fill the rest of the structure or return an
&EINVAL;. All formats are enumerable by beginning at index zero and
incrementing by one until <errorcode>EINVAL</errorcode> is
returned.</para>

    <para>Note that after switching input or output the list of enumerated image
formats may be different.</para>

    <table pgwide="1" frame="none" id="v4l2-fmtdesc">
      <title>struct <structname>v4l2_fmtdesc</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>index</structfield></entry>
	    <entry>Number of the format in the enumeration, set by
the application. This is in no way related to the <structfield>
pixelformat</structfield> field.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>type</structfield></entry>
	    <entry>Type of the data stream, set by the application.
Only these types are valid here:
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>,
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT_MPLANE</constant> and
<constant>V4L2_BUF_TYPE_VIDEO_OVERLAY</constant>. See <xref linkend="v4l2-buf-type" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>flags</structfield></entry>
	    <entry>See <xref linkend="fmtdesc-flags" /></entry>
	  </row>
	  <row>
	    <entry>__u8</entry>
	    <entry><structfield>description</structfield>[32]</entry>
	    <entry>Description of the format, a NUL-terminated ASCII
string. This information is intended for the user, for example: "YUV
4:2:2".</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>pixelformat</structfield></entry>
	    <entry>The image format identifier. This is a
four character code as computed by the v4l2_fourcc()
macro:</entry>
	  </row>
	  <row>
	    <entry spanname="hspan"><para><programlisting id="v4l2-fourcc">
#define v4l2_fourcc(a,b,c,d) (((__u32)(a)&lt;&lt;0)|((__u32)(b)&lt;&lt;8)|((__u32)(c)&lt;&lt;16)|((__u32)(d)&lt;&lt;24))
</programlisting></para><para>Several image formats are already
defined by this specification in <xref linkend="pixfmt" />. Note these
codes are not the same as those used in the Windows world.</para></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[4]</entry>
	    <entry>Reserved for future extensions. Drivers must set
the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="fmtdesc-flags">
      <title>Image Format Description Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_FMT_FLAG_COMPRESSED</constant></entry>
	    <entry>0x0001</entry>
	    <entry>This is a compressed format.</entry>
	  </row>
	  <row>
	    <entry><constant>V4L2_FMT_FLAG_EMULATED</constant></entry>
	    <entry>0x0002</entry>
	    <entry>This format is not native to the device but emulated
through software (usually libv4l2), where possible try to use a native format
instead for better performance.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>
  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The &v4l2-fmtdesc; <structfield>type</structfield>
is not supported or the <structfield>index</structfield> is out of
bounds.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>