[FFmpeg-user] Preserving AAC LC status when converting to fragmented MP4

[Moritz Barsnick]

On Mon, May 17, 2021 at 23:34:45 +0100, Simon Brown wrote:
> Thank you for your reply.  If it is the bitstream filter could you point me
> to the relevant source file that is responsible for this filter?

Sure, it's here:
https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/aac_adtstoasc_bsf.c

> mp4info doesn't deal with TS, as you surmise.  FFMpeg reports the output
> file as AAC (not LC).  I'm not sure VLC gives that detail.  But given that
> the ffmpeg processor and the mp4info program both seem to concur when there
> is or isn't AAC-LC I'm not sure there is much value in trying a third
> tool.

You could also try mediainfo. I also found a tool capable of parsing
and deconstruction AAC headers (https://p23.nl/projects/aac-header/),
but I don't trust it since it isn't capable of recognizing e.g.
HE-AACv2 (though I haven't taken the time to understand all the headers
myself).

I couldn't reproduce the loss of this information with the input
samples I have. Can you share your input file? Since it's an MPEG-TS.
perhaps the first MB (or five) suffice.

> I will download the latest prebuilt binaries for Windows and give it a try
> with those.  I'd still be interested in the source file responsible as the
> version on the embedded system I'm using is not the most recent build, and
> rebuilding for that isn't something I want to do at this stage.

I understand.

Cheers,
Moritz