Extracting 7.1 AAC as raw/ADTS with MP4Box: reported as 5.0?

[LigH]

I hope this thread fits here, as there are several tools and topics involved.

I got a report in the German doom9/Gleitz board that a member tried to extract raw streams (mp4box -raw *) from an MP4 file, supposedly containing 7.1 LC-AAC audio. Original material is not available as a small sample at the moment.

After re-multiplexing the extracted raw streams using MKVToolnix, the result does not play well in MPC-HC (gets stuck); ffplay reports issues and an AAC audio stream with 5.0 channel layout; only VLC plays it and detects the audio as 7.1 (3F2M2R/LFE). A small sample of the extracted AAC (https://forum.gleitz.info/showthread.php?47899-AAC-Stream-fixen&p=458982&viewfull=1#post458982) is detected as 5.0 (3/2/0) in MediaInfo as well.

My guess would be that the extraction to ADTS misses some header data, so I recommended not to demultiplex at all before converting to MKV, or at least save the audio as M4A instead of ADTS.

Can someone confirm? And is there any known small clip with 7.1 AAC audio I could download to test that issue?

[RBO]

Hi, GPAC contributor here. Please note that we prefer that you report in github issues if you think this is a bug.

It looks very similar to https://github.com/gpac/gpac/issues/183 that is fixed. Make sure you are using the latest MP4Box version.

[LigH]

Thank you for this link. A pity the sample linked there already expired...

AFAIR from the report in our German forum, the MP4Box was built recently. When I can get hold of a sample I can test myself, I will report there as well; but for now, I have no material (and the thread starter accidently overwrote his).

[nevcairiel]

If the AAC stream uses PCE, which for 7.1 is rather likely, then you'll need a rather recent version of the ffmpeg decoders to properly support that in ADTS - assuming the ADTS was exported properly in the first place.

[LigH]

PCE as in "Program Configuration Element"? OK, that gives me another keyword to investigate. As soon as I can get hold of any material. Any known demo clip downloads?
_

P.S.: Maybe I can convert some Dolby Trailers (https://thedigitaltheater.com/index.php/dolby-trailers/) ...
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P.P.S.: OK, for now I can confirm that MediaInfo reports only a 3/2/0 channel configuration for ADTS AAC extracted by GPAC DEV-rev206 mp4box out of M4A created from FLAC by QAAC, while it reports 3/2/2.1 for the same track in the M4A.

I will package a few files and publish it in the GPAC trac, with verbose reports of versions and command line parameters of used software.
_

GPAC trac issue #881 (https://github.com/gpac/gpac/issues/881)

The ffprobe error "channel element 1.2 is not allocated" sounds interesting to me. Also the detected bitrate (11 kbps) is suspicious.