Artefacts decoding Hobbit 4k trailer

[Carl Eugen Hoyos]

As reported on ​Doom9.
I will upload 78 frames from the Hobbit 4k trailer which are decoded with artefacts that the reference decoder does not show. The first 32 frames, 4 frames in the middle and the last frame (an IDR frame) are decoded bit-exact, the remaining frames are decoded differently than with the reference decoder.
Decoding is different (but also incorrect) with multithreading.

$ ffmpeg -threads 1 -i hobbit4k-artefacts.h264 -f null -
ffmpeg version N-53451-gd42106c Copyright (c) 2000-2013 the FFmpeg developers
  built on May 26 2013 14:59:18 with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl --disable-indev=jack
  libavutil      52. 34.100 / 52. 34.100
  libavcodec     55. 12.100 / 55. 12.100
  libavformat    55.  7.100 / 55.  7.100
  libavdevice    55.  1.101 / 55.  1.101
  libavfilter     3. 70.100 /  3. 70.100
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
Input #0, h264, from 'hobbit4k-artefacts.h264':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: h264 (High), yuv420p, 4096x2304, 23.98 fps, 23.98 tbr, 1200k tbn, 47.95 tbc
nb_threads: 0
Output #0, null, to 'pipe:':
  Metadata:
    encoder         : Lavf55.7.100
    Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 4096x2304, q=2-31, 200 kb/s, 90k tbn, 23.98 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (h264 -> rawvideo)
Press [q] to stop, [?] for help
[null @ 0x2f41c60] Encoder did not produce proper pts, making some up.
left block unavailable for requested intra4x4 mode -1 at 0 127A
[h264 @ 0x2f404e0] error while decoding MB 0 127
[h264 @ 0x2f404e0] Cannot use next picture in error concealment
[h264 @ 0x2f404e0] concealing 4401 DC, 4401 AC, 4401 MV errors in P frame
[h264 @ 0x2f404e0] left block unavailable for requested intra mode at 0 89
[h264 @ 0x2f404e0] error while decoding MB 0 89
[h264 @ 0x2f404e0] Cannot use next picture in error concealment
[h264 @ 0x2f404e0] concealing 14129 DC, 14129 AC, 14129 MV errors in P frame
left block unavailable for requested intra mode at 0 80rate=N/A
[h264 @ 0x2f404e0] error while decoding MB 0 80
[h264 @ 0x2f404e0] Cannot use next picture in error concealment
[h264 @ 0x2f404e0] concealing 16433 DC, 16433 AC, 16433 MV errors in P frame
left block unavailable for requested intra mode at 0 79rate=N/A
[h264 @ 0x2f404e0] error while decoding MB 0 79
[h264 @ 0x2f404e0] Cannot use next picture in error concealment
[h264 @ 0x2f404e0] concealing 16689 DC, 16689 AC, 16689 MV errors in P frame
frame=   78 fps= 37 q=0.0 Lsize=N/A time=00:00:03.25 bitrate=N/A
video:7kB audio:0kB subtitle:0 global headers:0kB muxing overhead -100.293803%

The original file contains additional three GOPs where decoding is not bitexact but no artefacts are visible, if this is a different issue, I will open a new ticket.

[Carl Eugen Hoyos]

Sample uploaded to samples/ffmpeg-bugs/trac/ticket2606

[Carl Eugen Hoyos]

Fixed by Michael.

[Clément Bœsch]

(in 826b3a75cd295c03720e00d3de83e1abcbedd4b9)