#4261: Systematic artefacts from 10bit Source
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Reporter: solidghost | Type: defect
Status: new | Priority: normal
Component: ffmpeg | Version:
Keywords: artefact | unspecified
Blocking: | Blocked By:
Analyzed by developer: 0 | Reproduced by developer: 0
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'''When encoding from a 10 bit source file or Prores 422 or 4444,
compression / color artefacts appear. From what I can see, the problem
lies in the "dc precision" command "-dc". I have tried different
combinations and these are my results.'''
On HD encodings '''”-dc8”''' will give you nice clean solid colors without
artifacts. But gradients and shading will suffer and be rougher.
On HD encodings '''”-dc11”''' will give you bad compression and color
artifacts that look very systematic as you can see in the picture in the
link. But the Gradients looks nice and smooth.
On SD encodings '''”-dc8”''' will give you nice clean solid colors without
artifacts. But gradients and shading will suffer and be rougher.
On SD encodings '''”-dc9”''' will give you bad compression and color
artifacts that look very systematic. But the Gradients looks nice and
smooth.
One theory is that FFmpeg uses an intermediate pix format that differs
from the source when interpolating the pixels...
From other encoding software’s if I mimic the settings, all the encodings
looks nice in all cases. So it seems that there is a bug in ffmpeg.
'''Here is an example of the ffmpeg command I use:'''
{{{
ffmpeg -i HD_uncompressed422_10bit.mov -vcodec mpeg2video -aspect
{$aspectRatio} -r 25 -pix_fmt yuv422p -timecode_frame_start 0 -minrate
150000k -maxrate 150000k -b 150000k -intra -flags +cgop -flags2
+ivlc+non_linear_q -dc 11 -sc_threshold 1000000000 -qscale 1 -qmin 1 -qmax
12 -bufsize 47185920 -rc_init_occupancy 47185920 -rc_buf_aggressivity 0.25
-s {$resolution} -vframes {$frameDuration} -an OUTPUT.m2v
}}}
'''ffmpeg version 2.5.2 and older'''
'''Example Picture. Download and zoom in. Specially on the left side grey
area.'''[https://images.creativecow.net/279525/artefacts_from_10_bit_source.png]
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Ticket URL: <https://trac.ffmpeg.org/ticket/4261>
FFmpeg <https://ffmpeg.org>
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