Opened 5 years ago

Closed 3 years ago

#3150 closed defect (fixed)

H.261 encoding: -cmp rd or sse ruins image quality

Reported by: maikmerten Owned by:
Priority: normal Component: avcodec
Version: git-master Keywords: h261
Cc: michael Blocked By:
Blocking: Reproduced by developer: yes
Analyzed by developer: no

Description

Summary of the bug:
How to reproduce:

ffmpeg -i /tmp/test.y4m -f h261 -vb 256k -cmp rd /tmp/test.h261

ffmpeg version N-58246-g7d0e927 Copyright (c) 2000-2013 the FFmpeg developers
  built on Nov 18 2013 17:15:01 with gcc 4.8 (Ubuntu/Linaro 4.8.1-10ubuntu8)

Test sequence used is http://media.xiph.org/video/derf/y4m/sign_irene_cif.y4m

Bitrate of the file is very much inflated by specifying the -cmp rd option, yet picture quality is severely affected by blockyness. Apparently the encoder is forced into aggressive quantization.

Attached picture shows one representative frame of video output.

Attachments (1)

test.png (298.3 KB) - added by maikmerten 5 years ago.

Download all attachments as: .zip

Change History (8)

Changed 5 years ago by maikmerten

comment:1 Changed 5 years ago by cehoyos

  • Keywords h261 added
  • Reproduced by developer set
  • Status changed from new to open

For future tickets: Please always provide your failing command line together with complete, uncut console output. If a problem is reproducible with -f lavfi -i testsrc please consider using it since it it may make reproducing the whole ticket easier.

Image quality starts to degrade after 20 seconds.

$ ffmpeg -f lavfi -i testsrc=s=352x288 -vb 256k -cmp rd -t 60 out.h261
ffmpeg version N-58249-g2974050 Copyright (c) 2000-2013 the FFmpeg developers
  built on Nov 18 2013 18:18:50 with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl
  libavutil      52. 53.100 / 52. 53.100
  libavcodec     55. 43.101 / 55. 43.101
  libavformat    55. 21.100 / 55. 21.100
  libavdevice    55.  5.100 / 55.  5.100
  libavfilter     3. 91.100 /  3. 91.100
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Input #0, lavfi, from 'testsrc=s=352x288':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: rawvideo (RGB[24] / 0x18424752), rgb24, 352x288 [SAR 1:1 DAR 11:9], 25 tbr, 25 tbn, 25 tbc
Output #0, h261, to 'out.h261':
  Metadata:
    encoder         : Lavf55.21.100
    Stream #0:0: Video: h261, yuv420p, 352x288 [SAR 1:1 DAR 11:9], q=2-31, 256 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> h261)
Press [q] to stop, [?] for help
[h261 @ 0x306e800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 16 times
[h261 @ 0x306e800] warning, clipping 2 dct coefficients to -127..127
    Last message repeated 1 times
[h261 @ 0x306e800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 4 times
[h261 @ 0x306e800] warning, clipping 2 dct coefficients to -127..127
    Last message repeated 1 times
[h261 @ 0x306e800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 5 times
[h261 @ 0x306e800] warning, clipping 2 dct coefficients to -127..127
[h261 @ 0x306e800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 12 times
[h261 @ 0x306e800] warning, clipping 2 dct coefficients to -127..127
[h261 @ 0x306e800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 76 times
[h261 @ 0x306e800] warning, clipping 1 dct coefficients to -127..127411.3kbits/s
    Last message repeated 47 times
frame= 1500 fps=606 q=31.0 Lsize=    3090kB time=00:01:00.00 bitrate= 422.0kbits/s
video:3090kB audio:0kB subtitle:0 global headers:0kB muxing overhead 0.000000%
Last edited 5 years ago by cehoyos (previous) (diff)

comment:2 Changed 5 years ago by michael

seems the -mbd rd fix, fixed this too

comment:3 Changed 5 years ago by cehoyos

  • Cc michael added

I still see the exact same artefacts (starting at ~20sec) with ddaf543:

$ ffmpeg -f lavfi -i testsrc=s=352x288 -vb 256k -cmp rd -t 60 out.h261
ffmpeg version N-58302-gddaf543 Copyright (c) 2000-2013 the FFmpeg developers
  built on Nov 20 2013 17:10:53 with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl
  libavutil      52. 53.100 / 52. 53.100
  libavcodec     55. 43.101 / 55. 43.101
  libavformat    55. 21.100 / 55. 21.100
  libavdevice    55.  5.100 / 55.  5.100
  libavfilter     3. 91.100 /  3. 91.100
  libswscale      2.  5.101 /  2.  5.101
  libswresample   0. 17.104 /  0. 17.104
  libpostproc    52.  3.100 / 52.  3.100
Input #0, lavfi, from 'testsrc=s=352x288':
  Duration: N/A, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: rawvideo (RGB[24] / 0x18424752), rgb24, 352x288 [SAR 1:1 DAR 11:9], 25 tbr, 25 tbn, 25 tbc
Output #0, h261, to 'out.h261':
  Metadata:
    encoder         : Lavf55.21.100
    Stream #0:0: Video: h261, yuv420p, 352x288 [SAR 1:1 DAR 11:9], q=2-31, 256 kb/s, 90k tbn, 25 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo -> h261)
Press [q] to stop, [?] for help
[h261 @ 0x3798800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 16 times
[h261 @ 0x3798800] warning, clipping 2 dct coefficients to -127..127
    Last message repeated 1 times
[h261 @ 0x3798800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 4 times
[h261 @ 0x3798800] warning, clipping 2 dct coefficients to -127..127
    Last message repeated 1 times
[h261 @ 0x3798800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 5 times
[h261 @ 0x3798800] warning, clipping 2 dct coefficients to -127..127
[h261 @ 0x3798800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 12 times
[h261 @ 0x3798800] warning, clipping 2 dct coefficients to -127..127
[h261 @ 0x3798800] warning, clipping 1 dct coefficients to -127..127
    Last message repeated 76 times
[h261 @ 0x3798800] warning, clipping 1 dct coefficients to -127..127409.5kbits/s
    Last message repeated 47 times
frame= 1500 fps=611 q=31.0 Lsize=    3090kB time=00:01:00.00 bitrate= 422.0kbits/s
video:3090kB audio:0kB subtitle:0 global headers:0kB muxing overhead 0.000000%

comment:4 Changed 4 years ago by michael

are you sure this is not an artifact of low bitrate h261 ?
do you see fewer artifacts with -cmp sse ?

comment:5 Changed 4 years ago by cehoyos

I tested the following:

$ ffmpeg -f lavfi -i testsrc=s=352x288 -vb 256k -t 60 -cmp sad outsad.h261

This encodes at 302.5kbits/s and the output file looks visually not great but acceptable (some artefacts are visible after 20 seconds, I originally thought that they were related to the codec and the bitrate.
I then tried:

$ ffmpeg -f lavfi -i testsrc=s=352x288 -vb 256k -t 60 -cmp rd outrd.h261

The output file outrd,h261 is encoded with 422.0kbits/s and looks visually significantly worse than outsad.h261 (starting from 20 seconds on, outsad.h261 also gets worse after 20 seconds, but still looks much better than outrd.h261).
-cmp sse produces an even larger file with similar artefacts as outrd.h261 but they start earlier.

If I encode only ten seconds, file size is similar for all three cmp modes (sad: 424.5kbits/s, rd: 414.8kbits/s, sse; 426.2kbits/s) and all three output files do not show obvious artefacts. If I should guess, I'd say there is a bug (that worsens h261 quality significantly after some encoding time) and some cmp modes make this bug much more visible than others (and the default sad).

The issue that -cmp 1 produces larger files with significantly more artefacts than -cmp 0 is not a regression, I can reproduce it with 1c3990db

comment:6 Changed 4 years ago by michael

  • Summary changed from H.261 encoding: "-cmp rd" ruins image quality to H.261 encoding: -cmp rd or sse ruins image quality

comment:7 Changed 3 years ago by michael

  • Resolution set to fixed
  • Status changed from open to closed
Note: See TracTickets for help on using tickets.