[Bug 771994] aacparse: Does not rezognize HE-AAC v2 stream

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=771994

--- Comment #5 from A Ashley <bugzilla at ashley-family.net> ---
(In reply to Olivier Crête from comment #4)
> I assume the parser need to find PS and SBR bits in the stream to know which
> profile it is?

It depends upon how the stream is encapsulated.

In the case of an MP4 file, the ES descriptor should contain the profile
information and if PS or SBR are being used. qtdemux should be passing that in
the caps, but I don't think it does currently.

If LATM/LOAS is used, the signalling can be put in the AudioSpecificConfig
section of StreamMuxConfig.

Ultimately the PS or SBR data goes in filler elements in the elementary stream.
An AAC-LC decoder would skip those and decode the base AAC-LC stream. An HE-AAC
or HE-AAC v2 decoder will know how to read this extra data and enhance the base
AAC-LC stream.

The following white paper from Fraunhofer has a good overview of the different
ways in which AAC can be encapsulated:

https://www.iis.fraunhofer.de/content/dam/iis/de/doc/ame/wp/FraunhoferIIS_Application-Bulletin_AAC-Transport-Formats.pdf

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