[FFmpeg-user] where ffmpeg parses mpeg audio headers?

[Paul B Mahol]

On Thu, Feb 1, 2024 at 5:45 PM Andrew Randrianasulu <randrianasulu at gmail.com>
wrote:

> I was looking into https://trac.ffmpeg.org/ticket/1258#comment:12
> (mpeg2 <https://trac.ffmpeg.org/ticket/1258#comment:12(mpeg2>
> multichannel audio in HDV) and reading documents linked  in
> this ticket.
>
> I still have very vague understanding  on where ffmpeg audio (PES?)
> headers read by ffmpeg
>
> somewhere in ffmpeg/libavformat/mpeg.c ?
>
> According to this picture https://ericdevos.be/kask/2BA/2BA
> videoformaten/MPEG-2 description.htm
>
> Figure 2 -- Structure of an MPEG-2 Audio block of data
>
> multichannel extension can be carried (partially!) in IEC 11172-3
> layer II frame. You just need to search in very beginning of ancillary
> data for Multichannel header.
>
> Extension stream,  touched in more details in  "An Implementation of the
> MPEG—2 Audio Decoding Specification by Chad Mikkelson" (p. 38) sounds a
> bit more mysterious to me: mc-capable encoder from dist10 [1] output
> extension stream as separate file only their decoder can read. I
> wonder how it must be interleaved in real system mpeg stream? And how
> it may work in transport stream (as used in HDV) ?
>
> [1] -  https://github.com/Randrianasulu/iso-dist10 (hopefully read
> sox-generated uncompressed multichannel 16 bit AIFF correctly).
>


I wish to reply, but I'm neither FFmpeg developer any more and also
consultation costs money and time.


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