[deliverable/linux.git] / Documentation / DocBook / media / v4l / vidioc-g-parm.xml

<refentry id="vidioc-g-parm">
  <refmeta>
    <refentrytitle>ioctl VIDIOC_G_PARM, VIDIOC_S_PARM</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>VIDIOC_G_PARM</refname>
    <refname>VIDIOC_S_PARM</refname>
    <refpurpose>Get or set streaming parameters</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>v4l2_streamparm *<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_PARM, VIDIOC_S_PARM</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>The current video standard determines a nominal number of
frames per second. If less than this number of frames is to be
captured or output, applications can request frame skipping or
duplicating on the driver side. This is especially useful when using
the <function>read()</function> or <function>write()</function>, which
are not augmented by timestamps or sequence counters, and to avoid
unnecessary data copying.</para>

    <para>Further these ioctls can be used to determine the number of
buffers used internally by a driver in read/write mode. For
implications see the section discussing the &func-read;
function.</para>

    <para>To get and set the streaming parameters applications call
the <constant>VIDIOC_G_PARM</constant> and
<constant>VIDIOC_S_PARM</constant> ioctl, respectively. They take a
pointer to a struct <structname>v4l2_streamparm</structname> which
contains a union holding separate parameters for input and output
devices.</para>

    <table pgwide="1" frame="none" id="v4l2-streamparm">
      <title>struct <structname>v4l2_streamparm</structname></title>
      <tgroup cols="4">
	&cs-ustr;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>type</structfield></entry>
	    <entry></entry>
	    <entry>The buffer (stream) type, same as &v4l2-format;
<structfield>type</structfield>, set by the application. See <xref
	    linkend="v4l2-buf-type" /></entry>
	  </row>
	  <row>
	    <entry>union</entry>
	    <entry><structfield>parm</structfield></entry>
	    <entry></entry>
	    <entry></entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>&v4l2-captureparm;</entry>
	    <entry><structfield>capture</structfield></entry>
	    <entry>Parameters for capture devices, used when
<structfield>type</structfield> is
<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>.</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>&v4l2-outputparm;</entry>
	    <entry><structfield>output</structfield></entry>
	    <entry>Parameters for output devices, used when
<structfield>type</structfield> is
<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>.</entry>
	  </row>
	  <row>
	    <entry></entry>
	    <entry>__u8</entry>
	    <entry><structfield>raw_data</structfield>[200]</entry>
	    <entry>A place holder for future extensions and custom
(driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and
higher.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="v4l2-captureparm">
      <title>struct <structname>v4l2_captureparm</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>capability</structfield></entry>
	    <entry>See <xref linkend="parm-caps" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>capturemode</structfield></entry>
	    <entry>Set by drivers and applications, see <xref linkend="parm-flags" />.</entry>
	  </row>
	  <row>
	    <entry>&v4l2-fract;</entry>
	    <entry><structfield>timeperframe</structfield></entry>
	    <entry><para>This is is the desired period between
successive frames captured by the driver, in seconds. The
field is intended to skip frames on the driver side, saving I/O
bandwidth.</para><para>Applications store here the desired frame
period, drivers return the actual frame period, which must be greater
or equal to the nominal frame period determined by the current video
standard (&v4l2-standard; <structfield>frameperiod</structfield>
field). Changing the video standard (also implicitly by switching the
video input) may reset this parameter to the nominal frame period. To
reset manually applications can just set this field to
zero.</para><para>Drivers support this function only when they set the
<constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
<structfield>capability</structfield> field.</para></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>extendedmode</structfield></entry>
	    <entry>Custom (driver specific) streaming parameters. When
unused, applications and drivers must set this field to zero.
Applications using this field should check the driver name and
version, see <xref linkend="querycap" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>readbuffers</structfield></entry>
	    <entry>Applications set this field to the desired number
of buffers used internally by the driver in &func-read; mode. Drivers
return the actual number of buffers. When an application requests zero
buffers, drivers should just return the current setting rather than
the minimum or an error code. For details see <xref
		linkend="rw" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[4]</entry>
	    <entry>Reserved for future extensions. Drivers and
applications must set the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="v4l2-outputparm">
      <title>struct <structname>v4l2_outputparm</structname></title>
      <tgroup cols="3">
	&cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>capability</structfield></entry>
	    <entry>See <xref linkend="parm-caps" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>outputmode</structfield></entry>
	    <entry>Set by drivers and applications, see <xref
	    linkend="parm-flags" />.</entry>
	  </row>
	  <row>
	    <entry>&v4l2-fract;</entry>
	    <entry><structfield>timeperframe</structfield></entry>
	    <entry>This is is the desired period between
successive frames output by the driver, in seconds.</entry>
	  </row>
	  <row>
	    <entry spanname="hspan"><para>The field is intended to
repeat frames on the driver side in &func-write; mode (in streaming
mode timestamps can be used to throttle the output), saving I/O
bandwidth.</para><para>Applications store here the desired frame
period, drivers return the actual frame period, which must be greater
or equal to the nominal frame period determined by the current video
standard (&v4l2-standard; <structfield>frameperiod</structfield>
field). Changing the video standard (also implicitly by switching the
video output) may reset this parameter to the nominal frame period. To
reset manually applications can just set this field to
zero.</para><para>Drivers support this function only when they set the
<constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
<structfield>capability</structfield> field.</para></entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>extendedmode</structfield></entry>
	    <entry>Custom (driver specific) streaming parameters. When
unused, applications and drivers must set this field to zero.
Applications using this field should check the driver name and
version, see <xref linkend="querycap" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>writebuffers</structfield></entry>
	    <entry>Applications set this field to the desired number
of buffers used internally by the driver in
<function>write()</function> mode. Drivers return the actual number of
buffers. When an application requests zero buffers, drivers should
just return the current setting rather than the minimum or an error
code. For details see <xref linkend="rw" />.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>reserved</structfield>[4]</entry>
	    <entry>Reserved for future extensions. Drivers and
applications must set the array to zero.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="parm-caps">
      <title>Streaming Parameters Capabilites</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_CAP_TIMEPERFRAME</constant></entry>
	    <entry>0x1000</entry>
	    <entry>The frame skipping/repeating controlled by the
<structfield>timeperframe</structfield> field is supported.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="parm-flags">
      <title>Capture Parameters Flags</title>
      <tgroup cols="3">
	&cs-def;
	<tbody valign="top">
	  <row>
	    <entry><constant>V4L2_MODE_HIGHQUALITY</constant></entry>
	    <entry>0x0001</entry>
	    <entry><para>High quality imaging mode. High quality mode
is intended for still imaging applications. The idea is to get the
best possible image quality that the hardware can deliver. It is not
defined how the driver writer may achieve that; it will depend on the
hardware and the ingenuity of the driver writer. High quality mode is
a different mode from the the regular motion video capture modes. In
high quality mode:<itemizedlist>
		  <listitem>
		    <para>The driver may be able to capture higher
resolutions than for motion capture.</para>
		  </listitem>
		  <listitem>
		    <para>The driver may support fewer pixel formats
than motion capture (eg; true color).</para>
		  </listitem>
		  <listitem>
		    <para>The driver may capture and arithmetically
combine multiple successive fields or frames to remove color edge
artifacts and reduce the noise in the video data.
</para>
		  </listitem>
		  <listitem>
		    <para>The driver may capture images in slices like
a scanner in order to handle larger format images than would otherwise
be possible. </para>
		  </listitem>
		  <listitem>
		    <para>An image capture operation may be
significantly slower than motion capture. </para>
		  </listitem>
		  <listitem>
		    <para>Moving objects in the image might have
excessive motion blur. </para>
		  </listitem>
		  <listitem>
		    <para>Capture might only work through the
<function>read()</function> call.</para>
		  </listitem>
		</itemizedlist></para></entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

  </refsect1>

  <refsect1>
    &return-value;
  </refsect1>
</refentry>
Commit	Line	Data
8e080c2e MCC	1	<refentry id="vidioc-g-parm">
	2	<refmeta>
	3	<refentrytitle>ioctl VIDIOC_G_PARM, VIDIOC_S_PARM</refentrytitle>
	4	&manvol;
	5	</refmeta>
	6
	7	<refnamediv>
	8	<refname>VIDIOC_G_PARM</refname>
	9	<refname>VIDIOC_S_PARM</refname>
	10	<refpurpose>Get or set streaming parameters</refpurpose>
	11	</refnamediv>
	12
	13	<refsynopsisdiv>
	14	<funcsynopsis>
	15	<funcprototype>
	16	<funcdef>int <function>ioctl</function></funcdef>
	17	<paramdef>int <parameter>fd</parameter></paramdef>
	18	<paramdef>int <parameter>request</parameter></paramdef>
	19	<paramdef>v4l2_streamparm *<parameter>argp</parameter></paramdef>
	20	</funcprototype>
	21	</funcsynopsis>
	22	</refsynopsisdiv>
	23
	24	<refsect1>
	25	<title>Arguments</title>
	26
	27	<variablelist>
	28	<varlistentry>
	29	<term><parameter>fd</parameter></term>
	30	<listitem>
	31	<para>&fd;</para>
	32	</listitem>
	33	</varlistentry>
	34	<varlistentry>
	35	<term><parameter>request</parameter></term>
	36	<listitem>
	37	<para>VIDIOC_G_PARM, VIDIOC_S_PARM</para>
	38	</listitem>
	39	</varlistentry>
	40	<varlistentry>
	41	<term><parameter>argp</parameter></term>
	42	<listitem>
	43	<para></para>
	44	</listitem>
	45	</varlistentry>
	46	</variablelist>
	47	</refsect1>
	48
	49	<refsect1>
	50	<title>Description</title>
	51
	52	<para>The current video standard determines a nominal number of
	53	frames per second. If less than this number of frames is to be
	54	captured or output, applications can request frame skipping or
	55	duplicating on the driver side. This is especially useful when using
	56	the <function>read()</function> or <function>write()</function>, which
	57	are not augmented by timestamps or sequence counters, and to avoid
3ad2f3fb	58	unnecessary data copying.</para>
8e080c2e MCC	59
	60	<para>Further these ioctls can be used to determine the number of
	61	buffers used internally by a driver in read/write mode. For
	62	implications see the section discussing the &func-read;
	63	function.</para>
	64
	65	<para>To get and set the streaming parameters applications call
	66	the <constant>VIDIOC_G_PARM</constant> and
	67	<constant>VIDIOC_S_PARM</constant> ioctl, respectively. They take a
	68	pointer to a struct <structname>v4l2_streamparm</structname> which
	69	contains a union holding separate parameters for input and output
	70	devices.</para>
	71
	72	<table pgwide="1" frame="none" id="v4l2-streamparm">
	73	<title>struct <structname>v4l2_streamparm</structname></title>
	74	<tgroup cols="4">
	75	&cs-ustr;
	76	<tbody valign="top">
	77	<row>
6016af82	78	<entry>__u32</entry>
8e080c2e MCC	79	<entry><structfield>type</structfield></entry>
	80	<entry></entry>
	81	<entry>The buffer (stream) type, same as &v4l2-format;
6016af82 SA	82	<structfield>type</structfield>, set by the application. See <xref
6016af82 SA	83	linkend="v4l2-buf-type" /></entry>
8e080c2e MCC	84	</row>
	85	<row>
	86	<entry>union</entry>
	87	<entry><structfield>parm</structfield></entry>
	88	<entry></entry>
	89	<entry></entry>
	90	</row>
	91	<row>
	92	<entry></entry>
	93	<entry>&v4l2-captureparm;</entry>
	94	<entry><structfield>capture</structfield></entry>
	95	<entry>Parameters for capture devices, used when
	96	<structfield>type</structfield> is
	97	<constant>V4L2_BUF_TYPE_VIDEO_CAPTURE</constant>.</entry>
	98	</row>
	99	<row>
	100	<entry></entry>
	101	<entry>&v4l2-outputparm;</entry>
	102	<entry><structfield>output</structfield></entry>
	103	<entry>Parameters for output devices, used when
	104	<structfield>type</structfield> is
	105	<constant>V4L2_BUF_TYPE_VIDEO_OUTPUT</constant>.</entry>
	106	</row>
	107	<row>
	108	<entry></entry>
	109	<entry>__u8</entry>
	110	<entry><structfield>raw_data</structfield>[200]</entry>
	111	<entry>A place holder for future extensions and custom
	112	(driver defined) buffer types <constant>V4L2_BUF_TYPE_PRIVATE</constant> and
	113	higher.</entry>
	114	</row>
	115	</tbody>
	116	</tgroup>
	117	</table>
	118
	119	<table pgwide="1" frame="none" id="v4l2-captureparm">
	120	<title>struct <structname>v4l2_captureparm</structname></title>
	121	<tgroup cols="3">
	122	&cs-str;
	123	<tbody valign="top">
	124	<row>
	125	<entry>__u32</entry>
	126	<entry><structfield>capability</structfield></entry>
	127	<entry>See <xref linkend="parm-caps" />.</entry>
	128	</row>
	129	<row>
	130	<entry>__u32</entry>
	131	<entry><structfield>capturemode</structfield></entry>
	132	<entry>Set by drivers and applications, see <xref linkend="parm-flags" />.</entry>
	133	</row>
	134	<row>
	135	<entry>&v4l2-fract;</entry>
	136	<entry><structfield>timeperframe</structfield></entry>
	137	<entry><para>This is is the desired period between
	138	successive frames captured by the driver, in seconds. The
	139	field is intended to skip frames on the driver side, saving I/O
	140	bandwidth.</para><para>Applications store here the desired frame
	141	period, drivers return the actual frame period, which must be greater
	142	or equal to the nominal frame period determined by the current video
	143	standard (&v4l2-standard; <structfield>frameperiod</structfield>
	144	field). Changing the video standard (also implicitly by switching the
	145	video input) may reset this parameter to the nominal frame period. To
	146	reset manually applications can just set this field to
	147	zero.</para><para>Drivers support this function only when they set the
148	<constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
149	<structfield>capability</structfield> field.</para></entry>
150	</row>
151	<row>
152	<entry>__u32</entry>
153	<entry><structfield>extendedmode</structfield></entry>
154	<entry>Custom (driver specific) streaming parameters. When
155	unused, applications and drivers must set this field to zero.
156	Applications using this field should check the driver name and
157	version, see <xref linkend="querycap" />.</entry>
158	</row>
159	<row>
160	<entry>__u32</entry>
161	<entry><structfield>readbuffers</structfield></entry>
162	<entry>Applications set this field to the desired number
163	of buffers used internally by the driver in &func-read; mode. Drivers
164	return the actual number of buffers. When an application requests zero
165	buffers, drivers should just return the current setting rather than
166	the minimum or an error code. For details see <xref
167	linkend="rw" />.</entry>
168	</row>
169	<row>
170	<entry>__u32</entry>
171	<entry><structfield>reserved</structfield>[4]</entry>
172	<entry>Reserved for future extensions. Drivers and
173	applications must set the array to zero.</entry>
174	</row>
175	</tbody>
176	</tgroup>
177	</table>
178
179	<table pgwide="1" frame="none" id="v4l2-outputparm">
180	<title>struct <structname>v4l2_outputparm</structname></title>
181	<tgroup cols="3">
182	&cs-str;
183	<tbody valign="top">
184	<row>
185	<entry>__u32</entry>
186	<entry><structfield>capability</structfield></entry>
187	<entry>See <xref linkend="parm-caps" />.</entry>
188	</row>
189	<row>
190	<entry>__u32</entry>
191	<entry><structfield>outputmode</structfield></entry>
192	<entry>Set by drivers and applications, see <xref
193	linkend="parm-flags" />.</entry>
194	</row>
195	<row>
196	<entry>&v4l2-fract;</entry>
197	<entry><structfield>timeperframe</structfield></entry>
198	<entry>This is is the desired period between
199	successive frames output by the driver, in seconds.</entry>
200	</row>
201	<row>
202	<entry spanname="hspan"><para>The field is intended to
203	repeat frames on the driver side in &func-write; mode (in streaming
204	mode timestamps can be used to throttle the output), saving I/O
205	bandwidth.</para><para>Applications store here the desired frame
206	period, drivers return the actual frame period, which must be greater
207	or equal to the nominal frame period determined by the current video
208	standard (&v4l2-standard; <structfield>frameperiod</structfield>
209	field). Changing the video standard (also implicitly by switching the
210	video output) may reset this parameter to the nominal frame period. To
211	reset manually applications can just set this field to
212	zero.</para><para>Drivers support this function only when they set the
213	<constant>V4L2_CAP_TIMEPERFRAME</constant> flag in the
214	<structfield>capability</structfield> field.</para></entry>
215	</row>
216	<row>
217	<entry>__u32</entry>
218	<entry><structfield>extendedmode</structfield></entry>
219	<entry>Custom (driver specific) streaming parameters. When
220	unused, applications and drivers must set this field to zero.
221	Applications using this field should check the driver name and
222	version, see <xref linkend="querycap" />.</entry>
223	</row>
224	<row>
225	<entry>__u32</entry>
226	<entry><structfield>writebuffers</structfield></entry>
227	<entry>Applications set this field to the desired number
228	of buffers used internally by the driver in
229	<function>write()</function> mode. Drivers return the actual number of
230	buffers. When an application requests zero buffers, drivers should
231	just return the current setting rather than the minimum or an error
232	code. For details see <xref linkend="rw" />.</entry>
233	</row>
234	<row>
235	<entry>__u32</entry>
236	<entry><structfield>reserved</structfield>[4]</entry>
237	<entry>Reserved for future extensions. Drivers and
238	applications must set the array to zero.</entry>
239	</row>
240	</tbody>
241	</tgroup>
242	</table>
243
244	<table pgwide="1" frame="none" id="parm-caps">
245	<title>Streaming Parameters Capabilites</title>
246	<tgroup cols="3">
247	&cs-def;
248	<tbody valign="top">
249	<row>
250	<entry><constant>V4L2_CAP_TIMEPERFRAME</constant></entry>
251	<entry>0x1000</entry>
252	<entry>The frame skipping/repeating controlled by the
253	<structfield>timeperframe</structfield> field is supported.</entry>
254	</row>
255	</tbody>
256	</tgroup>
257	</table>
258
259	<table pgwide="1" frame="none" id="parm-flags">
260	<title>Capture Parameters Flags</title>
261	<tgroup cols="3">
262	&cs-def;
263	<tbody valign="top">
264	<row>
265	<entry><constant>V4L2_MODE_HIGHQUALITY</constant></entry>
266	<entry>0x0001</entry>
267	<entry><para>High quality imaging mode. High quality mode
268	is intended for still imaging applications. The idea is to get the
269	best possible image quality that the hardware can deliver. It is not
270	defined how the driver writer may achieve that; it will depend on the
271	hardware and the ingenuity of the driver writer. High quality mode is
272	a different mode from the the regular motion video capture modes. In
273	high quality mode:<itemizedlist>
274	<listitem>
275	<para>The driver may be able to capture higher
276	resolutions than for motion capture.</para>
277	</listitem>
278	<listitem>
279	<para>The driver may support fewer pixel formats
280	than motion capture (eg; true color).</para>
281	</listitem>
282	<listitem>
283	<para>The driver may capture and arithmetically
284	combine multiple successive fields or frames to remove color edge
285	artifacts and reduce the noise in the video data.
286	</para>
287	</listitem>
288	<listitem>
289	<para>The driver may capture images in slices like
290	a scanner in order to handle larger format images than would otherwise
291	be possible. </para>
292	</listitem>
293	<listitem>
294	<para>An image capture operation may be
295	significantly slower than motion capture. </para>
296	</listitem>
297	<listitem>
298	<para>Moving objects in the image might have
299	excessive motion blur. </para>
300	</listitem>
301	<listitem>
302	<para>Capture might only work through the
303	<function>read()</function> call.</para>
304	</listitem>
305	</itemizedlist></para></entry>
306	</row>
307	</tbody>
308	</tgroup>
309	</table>
310
311	</refsect1>
312
313	<refsect1>
314	&return-value;
8e080c2e MCC	315	</refsect1>
8e080c2e MCC	316	</refentry>