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