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[media] DocBook media: document codec draining flow

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Document the interaction between VIDIOC_DECODER_CMD V4L2_DEC_CMD_STOP and
VIDIOC_ENCODER_CMD V4L2_ENC_CMD_STOP to start the draining, the V4L2_EVENT_EOS
event signalling all capture buffers are finished and ready to be dequeud,
the new V4L2_BUF_FLAG_LAST buffer flag indicating the last buffer being dequeued
from the capture queue, and the poll and VIDIOC_DQBUF ioctl return values once
the queue is drained.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
This commit is contained in:
Philipp Zabel 2015-05-04 07:51:04 -03:00 committed by Mauro Carvalho Chehab
parent 6425f646ff
commit 8cee396bfa
4 changed files with 40 additions and 2 deletions
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12
Documentation/DocBook/media/v4l/io.xml
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@ -1127,6 +1127,18 @@ passed on to a DMA-capable hardware unit for further processing or output.
Typically applications shall use this flag for output buffers if the data
in this buffer has not been created by the CPU but by some DMA-capable unit,
in which case caches have not been used.</entry>
</row>
<row>
<entry><constant>V4L2_BUF_FLAG_LAST</constant></entry>
<entry>0x00100000</entry>
<entry>Last buffer produced by the hardware. mem2mem codec drivers
set this flag on the capture queue for the last buffer when the
<link linkend="vidioc-querybuf">VIDIOC_QUERYBUF</link> or
<link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl is called. Due to hardware
limitations, the last buffer may be empty. In this case the driver will set the
<structfield>bytesused</structfield> field to 0, regardless of the format. Any
Any subsequent call to the <link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl
will not block anymore, but return an &EPIPE;.</entry>
</row>
<row>
<entry><constant>V4L2_BUF_FLAG_TIMESTAMP_MASK</constant></entry>

12
Documentation/DocBook/media/v4l/vidioc-decoder-cmd.xml
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@ -197,7 +197,17 @@ be muted when playing back at a non-standard speed.
this command does nothing. This command has two flags:
if <constant>V4L2_DEC_CMD_STOP_TO_BLACK</constant> is set, then the decoder will
set the picture to black after it stopped decoding. Otherwise the last image will
repeat. If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
repeat. mem2mem decoders will stop producing new frames altogether. They will send
a <constant>V4L2_EVENT_EOS</constant> event when the last frame has been decoded
and all frames are ready to be dequeued and will set the
<constant>V4L2_BUF_FLAG_LAST</constant> buffer flag on the last buffer of the
capture queue to indicate there will be no new buffers produced to dequeue. This
buffer may be empty, indicated by the driver setting the
<structfield>bytesused</structfield> field to 0. Once the
<constant>V4L2_BUF_FLAG_LAST</constant> flag was set, the
<link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl will not block anymore,
but return an &EPIPE;.
If <constant>V4L2_DEC_CMD_STOP_IMMEDIATELY</constant> is set, then the decoder
stops immediately (ignoring the <structfield>pts</structfield> value), otherwise it
will keep decoding until timestamp >= pts or until the last of the pending data from
its internal buffers was decoded.

10
Documentation/DocBook/media/v4l/vidioc-encoder-cmd.xml
View File

@ -129,7 +129,15 @@ this command.</entry>
encoding will continue until the end of the current <wordasword>Group
Of Pictures</wordasword>, otherwise encoding will stop immediately.
When the encoder is already stopped, this command does
nothing.</entry>
nothing. mem2mem encoders will send a <constant>V4L2_EVENT_EOS</constant> event
when the last frame has been decoded and all frames are ready to be dequeued and
will set the <constant>V4L2_BUF_FLAG_LAST</constant> buffer flag on the last
buffer of the capture queue to indicate there will be no new buffers produced to
dequeue. This buffer may be empty, indicated by the driver setting the
<structfield>bytesused</structfield> field to 0. Once the
<constant>V4L2_BUF_FLAG_LAST</constant> flag was set, the
<link linkend="vidioc-qbuf">VIDIOC_DQBUF</link> ioctl will not block anymore,
but return an &EPIPE;.</entry>
</row>
<row>
<entry><constant>V4L2_ENC_CMD_PAUSE</constant></entry>

8
Documentation/DocBook/media/v4l/vidioc-qbuf.xml
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@ -186,6 +186,14 @@ In that case the application should be able to safely reuse the buffer and
continue streaming.
</para>
</listitem>
<term><errorcode>EPIPE</errorcode></term>
<listitem>
<para><constant>VIDIOC_DQBUF</constant> returns this on an empty
capture queue for mem2mem codecs if a buffer with the
<constant>V4L2_BUF_FLAG_LAST</constant> was already dequeued and no new buffers
are expected to become available.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>