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media: uapi: h264: clarify V4L2_PIX_FMT_H264_SLICE format

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Document that the slice headers must be included for the benefit of
decoders that parse them (partially) in hardware, and that the start
code is optional. Add a link to the ITU-T Rec. H.264 specification
section that describes the slice format.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
This commit is contained in:
Philipp Zabel 2019-09-10 07:20:30 -03:00 committed by Mauro Carvalho Chehab
parent 9db5f87f67
commit 8255b4d219
1 changed files with 8 additions and 4 deletions
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12
Documentation/media/uapi/v4l/pixfmt-compressed.rst
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@ -61,10 +61,10 @@ Compressed Formats
- ``V4L2_PIX_FMT_H264_SLICE``
- 'S264'
- H264 parsed slice data, without the start code and as
extracted from the H264 bitstream. This format is adapted for
stateless video decoders that implement an H264 pipeline
(using the :ref:`mem2mem` and :ref:`media-request-api`).
- H264 parsed slice data, including slice headers, either with or
without the start code, as extracted from the H264 bitstream.
This format is adapted for stateless video decoders that implement an
H264 pipeline (using the :ref:`mem2mem` and :ref:`media-request-api`).
This pixelformat has two modifiers that must be set at least once
through the ``V4L2_CID_MPEG_VIDEO_H264_DECODE_MODE``
and ``V4L2_CID_MPEG_VIDEO_H264_START_CODE`` controls.
@ -80,6 +80,10 @@ Compressed Formats
appropriate number of macroblocks to decode a full
corresponding frame to the matching capture buffer.
The syntax for this format is documented in :ref:`h264`, section
7.3.2.8 "Slice layer without partitioning RBSP syntax" and the following
sections.
.. note::
This format is not yet part of the public kernel API and it