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media: doc: h264/hevc: Clarify _START_CODE_NONE meaning 

As some hardware have a knob to enable or disable emulation prevention
bytes removal, driver writers ended up wondering what exactly the
START_CODE_NONE modes meant in this regards. This patch clarify what is
expected with a reference to the specification.

Reported-by: John Cox <jc@kynesim.co.uk>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Nicolas Dufresne 2021-02-09 18:22:33 +01:00 committed by Mauro Carvalho Chehab
parent 6a49401e15
commit 21ea3defde
2 changed files with 6 additions and 2 deletions
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4
Documentation/userspace-api/media/v4l/ext-ctrls-codec-stateless.rst
View File

@ -769,7 +769,9 @@ Stateless Codec Control ID
* - ``V4L2_STATELESS_H264_START_CODE_NONE`` * - ``V4L2_STATELESS_H264_START_CODE_NONE``
- 0 - 0
- Selecting this value specifies that H264 slices are passed - Selecting this value specifies that H264 slices are passed
to the driver without any start code. to the driver without any start code. The bitstream data should be
according to :ref:`h264` 7.3.1 NAL unit syntax, hence contains
emulation prevention bytes when required.
* - ``V4L2_STATELESS_H264_START_CODE_ANNEX_B`` * - ``V4L2_STATELESS_H264_START_CODE_ANNEX_B``
- 1 - 1
- Selecting this value specifies that H264 slices are expected - Selecting this value specifies that H264 slices are expected

4
Documentation/userspace-api/media/v4l/ext-ctrls-codec.rst
View File

@ -3719,7 +3719,9 @@ enum v4l2_mpeg_video_hevc_size_of_length_field -
* - ``V4L2_MPEG_VIDEO_HEVC_START_CODE_NONE`` * - ``V4L2_MPEG_VIDEO_HEVC_START_CODE_NONE``
- 0 - 0
- Selecting this value specifies that HEVC slices are passed - Selecting this value specifies that HEVC slices are passed
to the driver without any start code. to the driver without any start code. The bitstream data should be
according to :ref:`hevc` 7.3.1.1 General NAL unit syntax, hence
contains emulation prevention bytes when required.
* - ``V4L2_MPEG_VIDEO_HEVC_START_CODE_ANNEX_B`` * - ``V4L2_MPEG_VIDEO_HEVC_START_CODE_ANNEX_B``
- 1 - 1
- Selecting this value specifies that HEVC slices are expected - Selecting this value specifies that HEVC slices are expected