[FFmpeg-trac] #3809(avcodec:new): Low-resolution MPEG-2 decoding incorrectly
FFmpeg
trac at avcodec.org
Mon Jul 28 12:40:39 CEST 2014
#3809: Low-resolution MPEG-2 decoding incorrectly
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Reporter: qyot27 | Type: defect
Status: new | Priority: normal
Component: avcodec | Version: git-master
Keywords: mpeg12dec | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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'''Summary of the bug:'''
Low-resolution (here defined as VCD resolution, 352x240) MPEG-2 files are
being decoded incorrectly in git master. The effect seems like the
bottom-most row of macroblocks in the image are smeared.
It occurs with low-res MPEG-2 streams encoded by HCenc, in which case it
seems any output plays back incorrectly, regardless of the presence of
soft pulldown. Low-res MPEG-2 streams encoded by FFmpeg work on playback
''initially'', but if soft pulldown is applied afterward, even these
streams begin showing the same problem. On a hardware DVD player the
playback is correct.
Using git bisect, the issue was introduced in commit 76b5e99 in January.
Prior to this commit, the streams decode correctly, and commenting out the
changes made in that commit from current git master also clears up the
issue. Of course, I recognize that the commit was made for a reason, so
it's probably more that a better check of some kind is necessary.
'''How to reproduce:'''
{{{
$ ./ffmpeg -i ../low_resolution_soft_pulldown.m2v
ffmpeg version N-65043-ga06c14a Copyright (c) 2000-2014 the FFmpeg
developers
built on Jul 28 2014 05:17:31 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
configuration: --enable-gpl --enable-version3 --disable-doc
--optflags=-O0
libavutil 52. 92.101 / 52. 92.101
libavcodec 55. 70.100 / 55. 70.100
libavformat 55. 49.100 / 55. 49.100
libavdevice 55. 13.102 / 55. 13.102
libavfilter 4. 11.102 / 4. 11.102
libswscale 2. 6.100 / 2. 6.100
libswresample 0. 19.100 / 0. 19.100
libpostproc 52. 3.100 / 52. 3.100
[mpeg1video @ 0x9e8db80] Warning MVs not available
[mpeg1video @ 0x9e8db80] concealing 44 DC, 44 AC, 44 MV errors in I frame
Input #0, mpegvideo, from '../low_resolution_soft_pulldown.m2v':
Duration: N/A, bitrate: N/A
Stream #0:0: Video: mpeg2video (Main), yuv420p(tv), 352x240 [SAR 10:11
DAR 4:3], max. 2000 kb/s, 29.97 fps, 59.94 tbr, 1200k tbn, 59.94 tbc
At least one output file must be specified
}}}
These particular warnings are repeated extensively during playback in
ffplay or during conversion:
[mpeg1video @ 03f5e6e0] Warning MVs not available
[mpeg1video @ 03f5e6e0] concealing 44 DC, 44 AC, 44 MV errors in I frame
--
Ticket URL: <https://trac.ffmpeg.org/ticket/3809>
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