MPNG artefacts

[Carl Eugen Hoyos]

The sample from ticket #2618 - ​http://samples.ffmpeg.org/PNG-seq/mpng.avi - shows artefacts.

$ ffmpeg -i mpng.avi out.avi
ffmpeg version N-54438-gf0bcb13 Copyright (c) 2000-2013 the FFmpeg developers
  built on Jul  4 2013 17:17:06 with gcc 4.7 (SUSE Linux)
  configuration:
  libavutil      52. 38.100 / 52. 38.100
  libavcodec     55. 18.100 / 55. 18.100
  libavformat    55. 11.100 / 55. 11.100
  libavdevice    55.  2.100 / 55.  2.100
  libavfilter     3. 78.100 /  3. 78.100
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
Input #0, avi, from 'mpng.avi':
  Duration: 00:00:04.00, start: 0.000000, bitrate: 8987 kb/s
    Stream #0:0: Video: png (MPNG / 0x474E504D), rgba, 160x120 [SAR 2834:2834 DAR 4:3], 40 tbr, 40 tbn, 40 tbc
[mpeg4 @ 0x2f5ebe0] too many threads/slices (9), reducing to 8
Output #0, avi, to 'out.avi':
  Metadata:
    ISFT            : Lavf55.11.100
    Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 160x120 [SAR 1:1 DAR 4:3], q=2-31, 200 kb/s, 40 tbn, 40 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (png -> mpeg4)
Press [q] to stop, [?] for help
Input stream #0:0 frame changed from size:160x120 fmt:rgba to size:160x120 fmt:rgb24
Input stream #0:0 frame changed from size:160x120 fmt:rgb24 to size:160x120 fmt:pal8
Input stream #0:0 frame changed from size:160x120 fmt:pal8 to size:160x120 fmt:gray
frame=  160 fps=0.0 q=6.6 Lsize=     206kB time=00:00:04.00 bitrate= 420.9kbits/s
video:196kB audio:0kB subtitle:0 global headers:0kB muxing overhead 4.825182%

[llogan]

Does anything play this without artefacts?

[Carl Eugen Hoyos]

Replying to llogan:

Does anything play this without artefacts?

I don't know, this ticket may be invalid.

[Christophe]

I think the ticket is invalid: the errors are block-like (I don't think incorrect decoding of pngs can lead to this) and were probably in the source of the mpng file.

One can extract the pngs (I'm actually impressed it works):
./ffmpeg -i mpng.avi -vcodec copy -an out%03d.png

And then the pngs can be decoded by any application, with the artifacts.

[Carl Eugen Hoyos]

Thank you for the analysis!