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

FFmpeg trac at avcodec.org
Wed Mar 6 01:12:55 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 brchapman):

 Replying to [comment:7 cehoyos]:
 > Replying to [comment:6 brchapman]:
 > > Replying to [comment:4 cehoyos]:
 > > > If there is an issue, it is a regression since 1edea05
 > > Just tried pulling that revision, and building. I still get the same
 > Since it is a regression since that revision, you will have to test an
 earlier version;-)
 Just tried pulling 0332324, and everything lines up great! there's no 2ms
 delay, and the other ticket about a duplicate first frame I posted #2324
 is also fixed!

 > > > Could you explain how you know that the delay is a bug?
 > > When converting through After Effects, I don't get this delay.
 Everything lines up exactly in the output wave file.
 > How does it "line up"? (I don't understand how the numbers should relate
 to the sound. I am certainly not claiming there is no issue - I don't know
 - but since we know already of three - very different - applications that
 decode the sample differently from After Effects, I wonder how you can be
 sure that it is correct.)

 I'm defining correct as placing the source mp4 and output wave file in a
 timeline together and checking if the waveforms match between them.  This
 is shown in the attached screenshot.  Since I'm not doing anything other
 than just reading a file in and encoding it to a different, I would expect
 the input and output sound to line up exactly.  Is this how you would
 expect it work?

 > > > Do you see the same problem if you extract the audio stream from the
 mov file with "ffmpeg -i test100.mp4 -acodec copy out.aac" ? Ie, is the
 problem in any way related to the container or only to aac?
 > > No, I don't get the delay. It lines up perfectly.
 > You mean you get the same delay if you use FFmpeg but no delay with
 After Effects if you try with the aac file - or do I misunderstand?
 When I run the command  "ffmpeg -i test100.mp4 -acodec copy out.aac", the
 out.aac file audio matches the source mp4's audio exactly, without any

Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2325#comment:8>
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