[FFmpeg-user] Create an AAC stream matching the Core Media Audio packet format / priming etc?

Christian Ebert blacktrash at gmx.net
Sat Apr 15 11:22:14 EEST 2017

* Mark Burton on Friday, April 14, 2017 at 22:44:52 +0100
>> On 14 Apr 2017, at 22:22, Christian Ebert <blacktrash at gmx.net> wrote:
>>>> Also, when you run with -v verbose, you'll see a delay (depends
>>>> on audio codec), for you case it's probably 1024. Maybe try:
>>>> -filter:a aresample=first_pts=0,asetpts=PTS-STARTPTS+1024
>>> 1024 looks correct. This method successfully changes the start, and the encoded audio plays, almost, 100% in sync. Its slightly cut off at the head, but only very slightly. However the downside of this method is that the audio now overruns the end of the picture further and is not trimmed from remaining samples I’m guessing. This results in a blank video frame being added to the tail of clip. ffprobe for ffmpeg_v3 attached.
>>> I tried using -shortest, but that didn’t help address the above issue.
>> Inserting
>> -t `ffprobe -v quiet -of default=nw=1:nk=1 -select_streams V -show_entries stream=duration SyncTest24p.mov`
>> into your commandline should do the trick.
> Adding '-t 2.000000’ to the command does help a little, but ultimately the final audio packet is still too large - 6ms in this case - and the black frame still occurs.

Works for me with all my sample results I checked.

Somewhat counterintuitive, but you never know:

-filter:a aresample=async=1:first_pts=0,asetpts=PTS-STARTPTS+1024

combined with the -t incantation.

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