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Based on kernel version 3.16. Page generated on 2014-08-06 21:39 EST.

1	<refentry id="vidioc-g-fmt">
2	  <refmeta>
3	    <refentrytitle>ioctl VIDIOC_G_FMT, VIDIOC_S_FMT,
4	VIDIOC_TRY_FMT</refentrytitle>
5	    &manvol;
6	  </refmeta>
7	
8	  <refnamediv>
9	    <refname>VIDIOC_G_FMT</refname>
10	    <refname>VIDIOC_S_FMT</refname>
11	    <refname>VIDIOC_TRY_FMT</refname>
12	    <refpurpose>Get or set the data format, try a format</refpurpose>
13	  </refnamediv>
14	
15	  <refsynopsisdiv>
16	    <funcsynopsis>
17	      <funcprototype>
18		<funcdef>int <function>ioctl</function></funcdef>
19		<paramdef>int <parameter>fd</parameter></paramdef>
20		<paramdef>int <parameter>request</parameter></paramdef>
21		<paramdef>struct v4l2_format
22	*<parameter>argp</parameter></paramdef>
23	      </funcprototype>
24	    </funcsynopsis>
25	  </refsynopsisdiv>
26	
27	  <refsect1>
28	    <title>Arguments</title>
29	
30	    <variablelist>
31	      <varlistentry>
32		<term><parameter>fd</parameter></term>
33		<listitem>
34		  <para>&fd;</para>
35		</listitem>
36	      </varlistentry>
37	      <varlistentry>
38		<term><parameter>request</parameter></term>
39		<listitem>
40		  <para>VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT</para>
41		</listitem>
42	      </varlistentry>
43	      <varlistentry>
44		<term><parameter>argp</parameter></term>
45		<listitem>
46		  <para></para>
47		</listitem>
48	      </varlistentry>
49	    </variablelist>
50	  </refsect1>
51	
52	  <refsect1>
53	    <title>Description</title>
54	
55	    <para>These ioctls are used to negotiate the format of data
56	(typically image format) exchanged between driver and
57	application.</para>
58	
59	    <para>To query the current parameters applications set the
60	<structfield>type</structfield> field of a struct
61	<structname>v4l2_format</structname> to the respective buffer (stream)
62	type. For example video capture devices use
63	<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant> or
64	<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE</constant>. When the application
65	calls the <constant>VIDIOC_G_FMT</constant> ioctl with a pointer to
66	this structure the driver fills the respective member of the
67	<structfield>fmt</structfield> union. In case of video capture devices
68	that is either the &v4l2-pix-format; <structfield>pix</structfield> or
69	the &v4l2-pix-format-mplane; <structfield>pix_mp</structfield> member.
70	When the requested buffer type is not supported drivers return an
71	&EINVAL;.</para>
72	
73	    <para>To change the current format parameters applications
74	initialize the <structfield>type</structfield> field and all
75	fields of the respective <structfield>fmt</structfield>
76	union member. For details see the documentation of the various devices
77	types in <xref linkend="devices" />. Good practice is to query the
78	current parameters first, and to
79	modify only those parameters not suitable for the application. When
80	the application calls the <constant>VIDIOC_S_FMT</constant> ioctl
81	with a pointer to a <structname>v4l2_format</structname> structure
82	the driver checks
83	and adjusts the parameters against hardware abilities. Drivers
84	should not return an error code unless the <structfield>type</structfield> field is invalid, this is
85	a mechanism to fathom device capabilities and to approach parameters
86	acceptable for both the application and driver. On success the driver
87	may program the hardware, allocate resources and generally prepare for
88	data exchange.
89	Finally the <constant>VIDIOC_S_FMT</constant> ioctl returns the
90	current format parameters as <constant>VIDIOC_G_FMT</constant> does.
91	Very simple, inflexible devices may even ignore all input and always
92	return the default parameters. However all V4L2 devices exchanging
93	data with the application must implement the
94	<constant>VIDIOC_G_FMT</constant> and
95	<constant>VIDIOC_S_FMT</constant> ioctl. When the requested buffer
96	type is not supported drivers return an &EINVAL; on a
97	<constant>VIDIOC_S_FMT</constant> attempt. When I/O is already in
98	progress or the resource is not available for other reasons drivers
99	return the &EBUSY;.</para>
100	
101	    <para>The <constant>VIDIOC_TRY_FMT</constant> ioctl is equivalent
102	to <constant>VIDIOC_S_FMT</constant> with one exception: it does not
103	change driver state. It can also be called at any time, never
104	returning <errorcode>EBUSY</errorcode>. This function is provided to
105	negotiate parameters, to learn about hardware limitations, without
106	disabling I/O or possibly time consuming hardware preparations.
107	Although strongly recommended drivers are not required to implement
108	this ioctl.</para>
109	
110	    <para>The format as returned by <constant>VIDIOC_TRY_FMT</constant>
111	must be identical to what <constant>VIDIOC_S_FMT</constant> returns for
112	the same input or output.</para>
113	
114	    <table pgwide="1" frame="none" id="v4l2-format">
115	      <title>struct <structname>v4l2_format</structname></title>
116	      <tgroup cols="4">
117		<colspec colname="c1" />
118		<colspec colname="c2" />
119		<colspec colname="c3" />
120		<colspec colname="c4" />
121		<tbody valign="top">
122		  <row>
123		    <entry>__u32</entry>
124		    <entry><structfield>type</structfield></entry>
125		    <entry></entry>
126		    <entry>Type of the data stream, see <xref
127			linkend="v4l2-buf-type" />.</entry>
128		  </row>
129		  <row>
130		    <entry>union</entry>
131		    <entry><structfield>fmt</structfield></entry>
132		  </row>
133		  <row>
134		    <entry></entry>
135		    <entry>&v4l2-pix-format;</entry>
136		    <entry><structfield>pix</structfield></entry>
137		    <entry>Definition of an image format, see <xref
138			linkend="pixfmt" />, used by video capture and output
139	devices.</entry>
140		  </row>
141		  <row>
142		    <entry></entry>
143		    <entry>&v4l2-pix-format-mplane;</entry>
144		    <entry><structfield>pix_mp</structfield></entry>
145		    <entry>Definition of an image format, see <xref
146			linkend="pixfmt" />, used by video capture and output
147	devices that support the <link linkend="planar-apis">multi-planar
148	version of the API</link>.</entry>
149		  </row>
150		  <row>
151		    <entry></entry>
152		    <entry>&v4l2-window;</entry>
153		    <entry><structfield>win</structfield></entry>
154		    <entry>Definition of an overlaid image, see <xref
155		    linkend="overlay" />, used by video overlay devices.</entry>
156		  </row>
157		  <row>
158		    <entry></entry>
159		    <entry>&v4l2-vbi-format;</entry>
160		    <entry><structfield>vbi</structfield></entry>
161		    <entry>Raw VBI capture or output parameters. This is
162	discussed in more detail in <xref linkend="raw-vbi" />. Used by raw VBI
163	capture and output devices.</entry>
164		  </row>
165		  <row>
166		    <entry></entry>
167		    <entry>&v4l2-sliced-vbi-format;</entry>
168		    <entry><structfield>sliced</structfield></entry>
169		    <entry>Sliced VBI capture or output parameters. See
170	<xref linkend="sliced" /> for details. Used by sliced VBI
171	capture and output devices.</entry>
172		  </row>
173		  <row>
174		    <entry></entry>
175		    <entry>&v4l2-sdr-format;</entry>
176		    <entry><structfield>sdr</structfield></entry>
177		    <entry>Definition of a data format, see
178	<xref linkend="pixfmt" />, used by SDR capture devices.</entry>
179		  </row>
180		  <row>
181		    <entry></entry>
182		    <entry>__u8</entry>
183		    <entry><structfield>raw_data</structfield>[200]</entry>
184		    <entry>Place holder for future extensions.</entry>
185		  </row>
186		</tbody>
187	      </tgroup>
188	    </table>
189	  </refsect1>
190	
191	  <refsect1>
192	    &return-value;
193	
194	    <variablelist>
195	      <varlistentry>
196		<term><errorcode>EINVAL</errorcode></term>
197		<listitem>
198		  <para>The &v4l2-format; <structfield>type</structfield>
199	field is invalid or the requested buffer type not supported.</para>
200		</listitem>
201	      </varlistentry>
202	    </variablelist>
203	  </refsect1>
204	</refentry>
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