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media: v4l2: clarify H.264 loop filter offset controls

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The venus and s5p-mfc drivers add the loop filter alpha/beta offset
controls V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_ALPHA/BETA with a range of
-6 to +6, inclusive. This is exactly the range specified for the slice
header fields slice_alpha_c0_offset_div2 and slice_beta_offset_div2,
which store half the actual filter offsets FilterOffsetA/B.

Clarify that this control contains the halved offsets.

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 2018-11-28 08:01:21 -05:00 committed by Mauro Carvalho Chehab
parent 91dc5e91ed
commit d338e17993
1 changed files with 6 additions and 0 deletions
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6
Documentation/media/uapi/v4l/extended-controls.rst
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@ -1117,10 +1117,16 @@ enum v4l2_mpeg_video_h264_loop_filter_mode -
``V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_ALPHA (integer)``
Loop filter alpha coefficient, defined in the H264 standard.
This value corresponds to the slice_alpha_c0_offset_div2 slice header
field, and should be in the range of -6 to +6, inclusive. The actual alpha
offset FilterOffsetA is twice this value.
Applicable to the H264 encoder.
``V4L2_CID_MPEG_VIDEO_H264_LOOP_FILTER_BETA (integer)``
Loop filter beta coefficient, defined in the H264 standard.
This corresponds to the slice_beta_offset_div2 slice header field, and
should be in the range of -6 to +6, inclusive. The actual beta offset
FilterOffsetB is twice this value.
Applicable to the H264 encoder.
.. _v4l2-mpeg-video-h264-entropy-mode: