Closed GoogleCodeExporter closed 8 years ago
I think this is because the frame size for AAC is 1024 samples.
509952 samples is 498 AAC frames.
I remember having similar issues with MP2 audio (also compounded by audio
frames overlapping).
Exactly the same happens on FFmpeg.
Original comment by mark.him...@gmail.com
on 5 Jul 2011 at 3:50
Thanks for that Mark.
So, if I understand correctly, FFmbc/FFmpeg are padding up to the frame size of
1024.
However, my input source has a SamplingCount of 508800 and the output has
509952, that shows a difference of 1152 samples - shouldn't that be less than
1024?
Thanks, Darren.
Original comment by boncey@gmail.com
on 5 Jul 2011 at 4:15
Because it's more complex than that.
You might not have noticed that the audio in your proxy is delayed by about
20ms.
I used exactly your command on your master.mov.
I then converted the audio from both the master.mov and proxy.mov to wavs, and
imported them into Audacity.
ffmbc -v 3 -i master.mov -vn -acodec pcm_s16le -ar 48000 master.wav
ffmbc -v 3 -i proxy.mov -vn -acodec pcm_s16le -ar 48000 proxy.wav
As you can see in the attached images, the audio is delayed by about 20ms and
there is a *small* section of extra audio at the end.
I am no expert, but I think the initial delay of ~20ms is 1 frame of aac
(you're extra 1024 samples) and then the extra at the end is the 128 samples.
When I was hitting this problem with MP2 audio it was explained that some
compressed audio codec's need some startup time. It might be worth asking these
questions on the ffmpeg-users email list to see if anyone knows more...
Hope that helps explain the issue you are seeing.
Original comment by mark.him...@gmail.com
on 5 Jul 2011 at 5:21
Attachments:
Thanks for your help Mark, we'll investigate in more detail at our end.
Original comment by boncey@gmail.com
on 13 Jul 2011 at 10:06
Original comment by baptiste...@gmail.com
on 26 Jul 2011 at 10:54
Original issue reported on code.google.com by
boncey@gmail.com
on 5 Jul 2011 at 10:49