Resolution-related artefacts with clearvideo

[Carl Eugen Hoyos]

Piotr kindly provided a new set of RealMedia files with Clearvideo content that shows heavy artefacts with FFmpeg but not RealPlayer.

$ ffmpeg -i bean2_324_500kbps_normal_encoding.rm -qscale 2 out.avi
ffmpeg version N-90888-gad16423 Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 6.4.0 (GCC)
  configuration: --enable-gpl
  libavutil      56. 17.100 / 56. 17.100
  libavcodec     58. 19.100 / 58. 19.100
  libavformat    58. 13.100 / 58. 13.100
  libavdevice    58.  4.100 / 58.  4.100
  libavfilter     7. 21.100 /  7. 21.100
  libswscale      5.  2.100 /  5.  2.100
  libswresample   3.  2.100 /  3.  2.100
  libpostproc    55.  2.100 / 55.  2.100
Input #0, rm, from 'bean2_324_500kbps_normal_encoding.rm':
  Metadata:
    title           : Title
    author          : Author
    copyright       : Copyrgiht
  Duration: 00:00:41.96, start: 0.000000, bitrate: 404 kb/s
    Stream #0:0: Video: clearvideo (CLV1 / 0x31564C43), yuv420p, 324x244, 500 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:
    INAM            : Title
    author          : Author
    ICOP            : Copyrgiht
    ISFT            : Lavf58.13.100
    Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 324x244, q=2-31, 200 kb/s, 15 fps, 15 tbn, 15 tbc
    Metadata:
      encoder         : Lavc58.19.100 mpeg4
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
frame=  630 fps=0.0 q=2.0 Lsize=   16164kB time=00:00:42.00 bitrate=3152.8kbits/s speed=81.4x
video:16143kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.127851%

The output looks horribly broken, the issue is apparently related to the width, 320 works fine now.

[ami_stuff]

added two more problematic samples

[ami_stuff]

added some more samples with different widths

308:240, 312:240, 316:240, 320:240, 340:240 decodes correctly with ffmpeg

296:240, 300:240, 304:240, 324:240, 328:240, 332:240, 336:240 decodes incorrecly

all of the samples plays fine with realplayer