[FFmpeg-trac] #5999(undetermined:new): Ffmpeg H264 decoder delays I-frames for some streams

[FFmpeg]

#5999: Ffmpeg H264 decoder delays I-frames for some streams
-------------------------------------+-------------------------------------
             Reporter:  mont3z       |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:  h264         |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
-------------------------------------+-------------------------------------

Comment (by mont3z):

 Thx, cehoyos. Please, see attachments for a sample stream from which
 frames get delayed although it only has I and P-frames. The workaround
 below avoids frame delays in streams without B-frames. Some times SPS also
 has num_reorder_frames != 0, so I think the configuration should precede
 SPS configuration values. I'm not an expert on this but I understand that
 somehow this needs to be set in decoder context.

 {{{
 --- a/ffmpeg-3.1.4/libavcodec/h264_ps.c Fri Nov 25 17:20:08 2016 -0800
 +++ b//ffmpeg-3.1.4/libavcodec/h264_ps.c Tue Dec 06 16:48:08 2016 -0800
 @@ -566,6 +566,8 @@
          }
      }

 +       sps->num_reorder_frames = 0;
 +
      if (!sps->sar.den)
          sps->sar.den = 1;
 }}}

 Result from {{{ffmpeg -i}}}:

 {{{
 ffmpeg -i test.h264
 ffmpeg version 3.1.4 Copyright (c) 2000-2016 the FFmpeg developers
   built with Microsoft (R) C/C++ Optimizing Compiler Version 18.00.40629
 for x64
   configuration: --arch=x86_64 --target-os=win64 --enable-ffmpeg --enable-
 shared --disable-gpl --enable-encoder='mjpeg,mpeg4,pcm_mulaw' --enable-
 bsfs
 --enable-decoder='mjpeg,mpeg4,h264,pcm_mulaw' --enable-
 filter='amix,aresample,rotate,crop,scale' --enable-muxer=mp4 --enable-
 demuxer=mov --enable-pars
 er=h264 --enable-protocol=file --prefix=/c/ffmpeg-3.1.4/out
 --toolchain=msvc --extra-ldflags=user32
 .lib
   libavutil      55. 28.100 / 55. 28.100
   libavcodec     57. 48.101 / 57. 48.101
   libavformat    57. 41.100 / 57. 41.100
   libavdevice    57.  0.101 / 57.  0.101
   libavfilter     6. 47.100 /  6. 47.100
   libswscale      4.  1.100 /  4.  1.100
   libswresample   2.  1.100 /  2.  1.100
 Input #0, h264, from 'test.h264':
   Duration: N/A, bitrate: N/A
     Stream #0:0: Video: h264 (High), yuv420p, 1920x1080 [SAR 1:1 DAR
 16:9], 30 fps, 30 tbr, 1200k tbn, 60 tbc
 At least one output file must be specified
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/5999#comment:2>
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