forked from Minki/linux
[media] v4l spec: document VIDIOC_(TRY_)DECODER_CMD
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
This commit is contained in:
Hans Verkuil
Mauro Carvalho Chehab
parent
a45c0ad51d
commit
6b4f12523d
@ -480,6 +480,7 @@ and discussions on the V4L mailing list.</revremark>
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&sub-cropcap;
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&sub-dbg-g-chip-ident;
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&sub-dbg-g-register;
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&sub-decoder-cmd;
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&sub-dqevent;
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&sub-encoder-cmd;
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&sub-enumaudio;
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256
Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
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256
Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
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@ -0,0 +1,256 @@
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<refentry id="vidioc-decoder-cmd">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_DECODER_CMD</refname>
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<refname>VIDIOC_TRY_DECODER_CMD</refname>
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<refpurpose>Execute an decoder command</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_decoder_cmd *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_DECODER_CMD, VIDIOC_TRY_DECODER_CMD</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<note>
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<title>Experimental</title>
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<para>This is an <link linkend="experimental">experimental</link>
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interface and may change in the future.</para>
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</note>
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<para>These ioctls control an audio/video (usually MPEG-) decoder.
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<constant>VIDIOC_DECODER_CMD</constant> sends a command to the
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decoder, <constant>VIDIOC_TRY_DECODER_CMD</constant> can be used to
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try a command without actually executing it. To send a command applications
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must initialize all fields of a &v4l2-decoder-cmd; and call
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<constant>VIDIOC_DECODER_CMD</constant> or <constant>VIDIOC_TRY_DECODER_CMD</constant>
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with a pointer to this structure.</para>
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<para>The <structfield>cmd</structfield> field must contain the
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command code. Some commands use the <structfield>flags</structfield> field for
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additional information.
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</para>
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<para>A <function>write</function>() or &VIDIOC-STREAMON; call sends an implicit
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START command to the decoder if it has not been started yet.
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</para>
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<para>A <function>close</function>() or &VIDIOC-STREAMOFF; call of a streaming
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file descriptor sends an implicit immediate STOP command to the decoder, and all
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buffered data is discarded.</para>
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<para>These ioctls are optional, not all drivers may support
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them. They were introduced in Linux 3.3.</para>
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<table pgwide="1" frame="none" id="v4l2-decoder-cmd">
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<title>struct <structname>v4l2_decoder_cmd</structname></title>
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<tgroup cols="5">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>cmd</structfield></entry>
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<entry></entry>
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<entry></entry>
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<entry>The decoder command, see <xref linkend="decoder-cmds" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry></entry>
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<entry></entry>
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<entry>Flags to go with the command. If no flags are defined for
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this command, drivers and applications must set this field to zero.</entry>
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</row>
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<row>
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<entry>union</entry>
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<entry>(anonymous)</entry>
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<entry></entry>
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<entry></entry>
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<entry></entry>
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</row>
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<row>
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<entry></entry>
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<entry>struct</entry>
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<entry><structfield>start</structfield></entry>
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<entry></entry>
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<entry>Structure containing additional data for the
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<constant>V4L2_DEC_CMD_START</constant> command.</entry>
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</row>
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<row>
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<entry></entry>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>speed</structfield></entry>
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<entry>Playback speed and direction. The playback speed is defined as
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<structfield>speed</structfield>/1000 of the normal speed. So 1000 is normal playback.
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Negative numbers denote reverse playback, so -1000 does reverse playback at normal
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speed. Speeds -1, 0 and 1 have special meanings: speed 0 is shorthand for 1000
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(normal playback). A speed of 1 steps just one frame forward, a speed of -1 steps
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just one frame back.
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</entry>
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</row>
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<row>
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<entry></entry>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>format</structfield></entry>
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<entry>Format restrictions. This field is set by the driver, not the
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application. Possible values are <constant>V4L2_DEC_START_FMT_NONE</constant> if
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there are no format restrictions or <constant>V4L2_DEC_START_FMT_GOP</constant>
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if the decoder operates on full GOPs (<wordasword>Group Of Pictures</wordasword>).
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This is usually the case for reverse playback: the decoder needs full GOPs, which
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it can then play in reverse order. So to implement reverse playback the application
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must feed the decoder the last GOP in the video file, then the GOP before that, etc. etc.
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</entry>
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</row>
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<row>
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<entry></entry>
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<entry>struct</entry>
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<entry><structfield>stop</structfield></entry>
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<entry></entry>
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<entry>Structure containing additional data for the
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<constant>V4L2_DEC_CMD_STOP</constant> command.</entry>
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</row>
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<row>
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<entry></entry>
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<entry></entry>
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<entry>__u64</entry>
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<entry><structfield>pts</structfield></entry>
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<entry>Stop playback at this <structfield>pts</structfield> or immediately
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if the playback is already past that timestamp. Leave to 0 if you want to stop after the
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last frame was decoded.
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</entry>
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</row>
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<row>
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<entry></entry>
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<entry>struct</entry>
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<entry><structfield>raw</structfield></entry>
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<entry></entry>
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<entry></entry>
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</row>
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<row>
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<entry></entry>
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<entry></entry>
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<entry>__u32</entry>
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<entry><structfield>data</structfield>[16]</entry>
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<entry>Reserved for future extensions. Drivers and
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applications must set the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="decoder-cmds">
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<title>Decoder Commands</title>
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<tgroup cols="3">
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&cs-def;
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_DEC_CMD_START</constant></entry>
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<entry>0</entry>
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<entry>Start the decoder. When the decoder is already
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running or paused, this command will just change the playback speed.
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That means that calling <constant>V4L2_DEC_CMD_START</constant> when
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the decoder was paused will <emphasis>not</emphasis> resume the decoder.
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You have to explicitly call <constant>V4L2_DEC_CMD_RESUME</constant> for that.
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This command has one flag:
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<constant>V4L2_DEC_CMD_START_MUTE_AUDIO</constant>. If set, then audio will
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be muted when playing back at a non-standard speed.
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</entry>
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</row>
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<row>
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<entry><constant>V4L2_DEC_CMD_STOP</constant></entry>
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<entry>1</entry>
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<entry>Stop the decoder. When the decoder is already stopped,
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this command does nothing. This command has two flags:
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if <constant>V4L2_DEC_CMD_STOP_TO_BLACK</constant> is set, then the decoder will
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set the picture to black after it stopped decoding. Otherwise the last image will
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repeat. If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
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stops immediately (ignoring the <structfield>pts</structfield> value), otherwise it
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will keep decoding until timestamp >= pts or until the last of the pending data from
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its internal buffers was decoded.
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</entry>
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</row>
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<row>
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<entry><constant>V4L2_DEC_CMD_PAUSE</constant></entry>
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<entry>2</entry>
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<entry>Pause the decoder. When the decoder has not been
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started yet, the driver will return an &EPERM;. When the decoder is
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already paused, this command does nothing. This command has one flag:
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if <constant>V4L2_DEC_CMD_PAUSE_TO_BLACK</constant> is set, then set the
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decoder output to black when paused.
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</entry>
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</row>
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<row>
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<entry><constant>V4L2_DEC_CMD_RESUME</constant></entry>
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<entry>3</entry>
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<entry>Resume decoding after a PAUSE command. When the
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decoder has not been started yet, the driver will return an &EPERM;.
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When the decoder is already running, this command does nothing. No
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flags are defined for this command.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The <structfield>cmd</structfield> field is invalid.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EPERM</errorcode></term>
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<listitem>
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<para>The application sent a PAUSE or RESUME command when
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the decoder was not running.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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@ -74,15 +74,16 @@ only used by the STOP command and contains one bit: If the
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encoding will continue until the end of the current <wordasword>Group
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Of Pictures</wordasword>, otherwise it will stop immediately.</para>
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<para>A <function>read</function>() call sends a START command to
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the encoder if it has not been started yet. After a STOP command,
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<para>A <function>read</function>() or &VIDIOC-STREAMON; call sends an implicit
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START command to the encoder if it has not been started yet. After a STOP command,
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<function>read</function>() calls will read the remaining data
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buffered by the driver. When the buffer is empty,
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<function>read</function>() will return zero and the next
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<function>read</function>() call will restart the encoder.</para>
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<para>A <function>close</function>() call sends an immediate STOP
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to the encoder, and all buffered data is discarded.</para>
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<para>A <function>close</function>() or &VIDIOC-STREAMOFF; call of a streaming
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file descriptor sends an implicit immediate STOP to the encoder, and all buffered
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data is discarded.</para>
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<para>These ioctls are optional, not all drivers may support
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them. They were introduced in Linux 2.6.21.</para>
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