About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / DocBook / media / v4l / vidioc-decoder-cmd.xml




Custom Search

Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

1	<refentry id="vidioc-decoder-cmd">
2	  <refmeta>
3	    <refentrytitle>ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</refentrytitle>
4	    &manvol;
5	  </refmeta>
6	
7	  <refnamediv>
8	    <refname>VIDIOC_DECODER_CMD</refname>
9	    <refname>VIDIOC_TRY_DECODER_CMD</refname>
10	    <refpurpose>Execute an decoder command</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>struct v4l2_decoder_cmd *<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_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</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>These ioctls control an audio/video (usually MPEG-) decoder.
53	<constant>VIDIOC_DECODER_CMD</constant> sends a command to the
54	decoder, <constant>VIDIOC_TRY_DECODER_CMD</constant> can be used to
55	try a command without actually executing it. To send a command applications
56	must initialize all fields of a &v4l2-decoder-cmd; and call
57	<constant>VIDIOC_DECODER_CMD</constant> or <constant>VIDIOC_TRY_DECODER_CMD</constant>
58	with a pointer to this structure.</para>
59	
60	    <para>The <structfield>cmd</structfield> field must contain the
61	command code. Some commands use the <structfield>flags</structfield> field for
62	additional information.
63	</para>
64	
65	    <para>A <function>write</function>() or &VIDIOC-STREAMON; call sends an implicit
66	START command to the decoder if it has not been started yet.
67	</para>
68	
69	    <para>A <function>close</function>() or &VIDIOC-STREAMOFF; call of a streaming
70	file descriptor sends an implicit immediate STOP command to the decoder, and all
71	buffered data is discarded.</para>
72	
73	    <para>These ioctls are optional, not all drivers may support
74	them. They were introduced in Linux 3.3.</para>
75	
76	    <table pgwide="1" frame="none" id="v4l2-decoder-cmd">
77	      <title>struct <structname>v4l2_decoder_cmd</structname></title>
78	      <tgroup cols="5">
79		&cs-str;
80		<tbody valign="top">
81		  <row>
82		    <entry>__u32</entry>
83		    <entry><structfield>cmd</structfield></entry>
84	            <entry></entry>
85	            <entry></entry>
86		    <entry>The decoder command, see <xref linkend="decoder-cmds" />.</entry>
87		  </row>
88		  <row>
89		    <entry>__u32</entry>
90		    <entry><structfield>flags</structfield></entry>
91	            <entry></entry>
92	            <entry></entry>
93		    <entry>Flags to go with the command. If no flags are defined for
94	this command, drivers and applications must set this field to zero.</entry>
95		  </row>
96		  <row>
97		    <entry>union</entry>
98		    <entry>(anonymous)</entry>
99	            <entry></entry>
100		    <entry></entry>
101	            <entry></entry>
102		  </row>
103		  <row>
104		    <entry></entry>
105		    <entry>struct</entry>
106	            <entry><structfield>start</structfield></entry>
107	            <entry></entry>
108	            <entry>Structure containing additional data for the
109	<constant>V4L2_DEC_CMD_START</constant> command.</entry>
110		  </row>
111		  <row>
112	            <entry></entry>
113	            <entry></entry>
114		    <entry>__s32</entry>
115		    <entry><structfield>speed</structfield></entry>
116	            <entry>Playback speed and direction. The playback speed is defined as
117	<structfield>speed</structfield>/1000 of the normal speed. So 1000 is normal playback.
118	Negative numbers denote reverse playback, so -1000 does reverse playback at normal
119	speed. Speeds -1, 0 and 1 have special meanings: speed 0 is shorthand for 1000
120	(normal playback). A speed of 1 steps just one frame forward, a speed of -1 steps
121	just one frame back.
122		    </entry>
123		  </row>
124		  <row>
125	            <entry></entry>
126	            <entry></entry>
127		    <entry>__u32</entry>
128		    <entry><structfield>format</structfield></entry>
129	            <entry>Format restrictions. This field is set by the driver, not the
130	application. Possible values are <constant>V4L2_DEC_START_FMT_NONE</constant> if
131	there are no format restrictions or <constant>V4L2_DEC_START_FMT_GOP</constant>
132	if the decoder operates on full GOPs (<wordasword>Group Of Pictures</wordasword>).
133	This is usually the case for reverse playback: the decoder needs full GOPs, which
134	it can then play in reverse order. So to implement reverse playback the application
135	must feed the decoder the last GOP in the video file, then the GOP before that, etc. etc.
136		    </entry>
137		  </row>
138		  <row>
139		    <entry></entry>
140		    <entry>struct</entry>
141	            <entry><structfield>stop</structfield></entry>
142	            <entry></entry>
143	            <entry>Structure containing additional data for the
144	<constant>V4L2_DEC_CMD_STOP</constant> command.</entry>
145		  </row>
146		  <row>
147	            <entry></entry>
148	            <entry></entry>
149		    <entry>__u64</entry>
150		    <entry><structfield>pts</structfield></entry>
151	            <entry>Stop playback at this <structfield>pts</structfield> or immediately
152	if the playback is already past that timestamp. Leave to 0 if you want to stop after the
153	last frame was decoded.
154		    </entry>
155		  </row>
156		  <row>
157		    <entry></entry>
158		    <entry>struct</entry>
159	            <entry><structfield>raw</structfield></entry>
160	            <entry></entry>
161	            <entry></entry>
162		  </row>
163		  <row>
164	            <entry></entry>
165	            <entry></entry>
166		    <entry>__u32</entry>
167		    <entry><structfield>data</structfield>[16]</entry>
168		    <entry>Reserved for future extensions. Drivers and
169	applications must set the array to zero.</entry>
170		  </row>
171		</tbody>
172	      </tgroup>
173	    </table>
174	
175	    <table pgwide="1" frame="none" id="decoder-cmds">
176	      <title>Decoder Commands</title>
177	      <tgroup cols="3">
178		&cs-def;
179		<tbody valign="top">
180		  <row>
181		    <entry><constant>V4L2_DEC_CMD_START</constant></entry>
182		    <entry>0</entry>
183		    <entry>Start the decoder. When the decoder is already
184	running or paused, this command will just change the playback speed.
185	That means that calling <constant>V4L2_DEC_CMD_START</constant> when
186	the decoder was paused will <emphasis>not</emphasis> resume the decoder.
187	You have to explicitly call <constant>V4L2_DEC_CMD_RESUME</constant> for that.
188	This command has one flag:
189	<constant>V4L2_DEC_CMD_START_MUTE_AUDIO</constant>. If set, then audio will
190	be muted when playing back at a non-standard speed.
191	            </entry>
192		  </row>
193		  <row>
194		    <entry><constant>V4L2_DEC_CMD_STOP</constant></entry>
195		    <entry>1</entry>
196		    <entry>Stop the decoder. When the decoder is already stopped,
197	this command does nothing. This command has two flags:
198	if <constant>V4L2_DEC_CMD_STOP_TO_BLACK</constant> is set, then the decoder will
199	set the picture to black after it stopped decoding. Otherwise the last image will
200	repeat. If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
201	stops immediately (ignoring the <structfield>pts</structfield> value), otherwise it
202	will keep decoding until timestamp >= pts or until the last of the pending data from
203	its internal buffers was decoded.
204	</entry>
205		  </row>
206		  <row>
207		    <entry><constant>V4L2_DEC_CMD_PAUSE</constant></entry>
208		    <entry>2</entry>
209		    <entry>Pause the decoder. When the decoder has not been
210	started yet, the driver will return an &EPERM;. When the decoder is
211	already paused, this command does nothing. This command has one flag:
212	if <constant>V4L2_DEC_CMD_PAUSE_TO_BLACK</constant> is set, then set the
213	decoder output to black when paused.
214	</entry>
215		  </row>
216		  <row>
217		    <entry><constant>V4L2_DEC_CMD_RESUME</constant></entry>
218		    <entry>3</entry>
219		    <entry>Resume decoding after a PAUSE command. When the
220	decoder has not been started yet, the driver will return an &EPERM;.
221	When the decoder is already running, this command does nothing. No
222	flags are defined for this command.</entry>
223		  </row>
224		</tbody>
225	      </tgroup>
226	    </table>
227	
228	  </refsect1>
229	
230	  <refsect1>
231	    &return-value;
232	
233	    <variablelist>
234	      <varlistentry>
235		<term><errorcode>EINVAL</errorcode></term>
236		<listitem>
237		  <para>The <structfield>cmd</structfield> field is invalid.</para>
238		</listitem>
239	      </varlistentry>
240	      <varlistentry>
241		<term><errorcode>EPERM</errorcode></term>
242		<listitem>
243		  <para>The application sent a PAUSE or RESUME command when
244	the decoder was not running.</para>
245		</listitem>
246	      </varlistentry>
247	    </variablelist>
248	  </refsect1>
249	</refentry>
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.