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

FFmpeg trac at avcodec.org
Wed Mar 6 11:17:58 CET 2013

#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 cehoyos):

 Replying to [comment:10 brchapman]:
 > Also, if I encode test100.mp4 without the aac audio stream (ie with no
 audio) and then convert it:
 > {{{
 > % ffmpeg -i test100_no_aac.mp4 -c:v prores test100_ffmpeg.mov
 > }}}
 > I don't get the duplicate first frame bug in #2324

 You are using a different input file that is cfr, your original sample has
 a longer first frame (that needs to be duplicated to get cfr output).

 > Based on this I would guess that this would work:
 > {{{
 > ffmpeg -i test100.mp4 -c:v prores -an test100_ffmpeg.mov
 > }}}
 > However, it doesn't. The first frame is still duplicated.

 Because the timestamps still require a duplication (they do not change
 just because you don't encode the audio). Use -vsync 0 to ignore the
 timestamps so that no frame duplication happens.

Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2325#comment:11>
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