[FFmpeg-trac] #7122(avcodec:new): Massive artefacts when decoding clearvideo

[FFmpeg]

#7122: Massive artefacts when decoding clearvideo
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               Reporter:  cehoyos     |                  Owner:
                   Type:  defect      |                 Status:  new
               Priority:  normal      |              Component:  avcodec
                Version:  git-master  |               Keywords:  clv
             Blocked By:              |               Blocking:
Reproduced by developer:  0           |  Analyzed by developer:  0
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 The low-bitrate samples from ticket #6842 show massive artefacts when
 decoded with current FFmpeg.
 {{{
 $ ffmpeg -i clv1_100kbps.rm -qscale 2 out.avi
 ffmpeg version N-90597-g673604e Copyright (c) 2000-2018 the FFmpeg
 developers
   built with gcc 6.3.0 (GCC)
   configuration: --enable-gpl
   libavutil      56. 13.100 / 56. 13.100
   libavcodec     58. 17.100 / 58. 17.100
   libavformat    58. 10.100 / 58. 10.100
   libavdevice    58.  2.100 / 58.  2.100
   libavfilter     7. 14.100 /  7. 14.100
   libswscale      5.  0.102 /  5.  0.102
   libswresample   3.  0.101 /  3.  0.101
   libpostproc    55.  0.100 / 55.  0.100
 Input #0, rm, from 'clv1_100kbps.rm':
   Duration: 00:00:03.20, start: 0.000000, bitrate: 74 kb/s
     Stream #0:0: Video: clearvideo (CLV1 / 0x31564C43), yuv420p, 320x240,
 100 kb/s, 15 fps, 15 tbr, 1k tbn, 1k tbc
 Please use -q:a or -q:v, -qscale is ambiguous
 Stream mapping:
   Stream #0:0 -> #0:0 (clearvideo (native) -> mpeg4 (native))
 Press [q] to stop, [?] for help
 Output #0, avi, to 'out.avi':
   Metadata:
     ISFT            : Lavf58.10.100
     Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 320x240,
 q=2-31, 200 kb/s, 15 fps, 15 tbn, 15 tbc
     Metadata:
       encoder         : Lavc58.17.100 mpeg4
     Side data:
       cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
 frame=   32 fps=0.0 q=2.0 Lsize=     250kB time=00:00:03.20 bitrate=
 638.9kbits/s speed= 123x
 video:243kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 2.757215%
 }}}
 The output video is recognizable but looks very ugly.

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Ticket URL: <https://trac.ffmpeg.org/ticket/7122>
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