[FFmpeg-trac] #2325(undetermined:new): MP4 AAC Audio is delayed by 2ms when converted to PCM

FFmpeg trac at avcodec.org
Sun Sep 13 18:49:03 CEST 2015

#2325: MP4 AAC Audio is delayed by 2ms when converted to PCM
             Reporter:  brchapman    |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  important    |                Component:
              Version:  git-master   |  undetermined
             Keywords:  aac mov      |               Resolution:
  regression                         |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |

Comment (by rmk):

 I have run into this as well and the way I see it, ffmpeg reads but does
 not write the custom mov metadata (udta/meta) "iTunSMPB". Check around
 line 3121 in mov.c where priming is set based on the values from that
 metadata entry. It the mov muxer wrote that metadata, ffmpeg would at
 least be compatible with itself as far as priming is concerned (i.e. not
 decode an offset) and with Apple tools. That would be an improvement. I
 don't know if trailing samples are treated in any way in ffmpeg but AFAIC
 the priming problem is the more serious one as it leads to a/v desync when
 the delay is long enough (2112 samples is what Apple uses by default and
 that's a bit more than a 25 FPS video frame and that's
 noticable/significant for some people).

 For further explanations see also http://ffmpeg.org/pipermail/ffmpeg-

Ticket URL: <https://trac.ffmpeg.org/ticket/2325#comment:16>
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