[M4IF Technotes] Is standard conform to put mp3 sound in aMPEG-4 stream ?

[AVARO Olivier FTRD/DIH/REN]

Well yes, it does mean that QT6 doesn't do layer 3 in MP4.  QT6 supports
a few profiles in MP4, and we currently don't cover the 'old' formats
(MPEG1 and MPEG2) in an MP4 context.
I'd be curious to know, however, if we have the same understanding of
the structures which would say "this is layer3 audio".  can you briefly
summarize your understanding of the profile, level, streamtype,
objecttype,  decoderspecificinfo, and access unit format? 
Since MP3 is a spec. that MPEG *owns*, I think it will be a very
valuable contribution to clarify all this in the MPEG spec.
I think streamtype and objecttype are very clear : 
- streamtype shall be 0x05 (this is an AudiioStream)
- objecttype shall be 0x6B (this is Audio ISO/IEC 11172-3 MPEG-1 Audio)
(Maybe we could have more depending on P&L of ISO/IEC 11172-3).
For decoderspecficinfo, although we could make something elaborate, I
guess we can also leave it empty and rely on the *in-band* signaling of
MP3.This needs further thought however (such as to investigate if P&L
for 11172-3  are properly signalled in MP3 files).
Concerning Access Unit definition, yes, this needs to be clarified and
findthe could trade-off between being consistent with the MPEG-4
framework and minimize the transformation of MP3 files.
As far as MPEG-4 Audio Profile and Level are concerned, I concur with
Rob, if there is a demand for MPEG-4 P&L supporting MP3, this can be
done. This could also be done in industry fora like ISMA (ex : "we
support this and this MPEG-4 P&L + MP3"). 
Kind regards,
Olivier
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