[M4IF Technotes] MPEG-4 AAC-LC: Buggy Conformance Streams

[Umang Garg]

  Dear Members, Hello,
I understand that the MPEG-4 AAC-LC conformance streams are available at 
the following FTP site:
ftp://mpaudconf:adif2mp4@ftp.iis.fhg.de/mpeg4audio-conformance
I currently have with me an ISO provided 'reference software' that 
contains the MPEG-4 AAC Decoder ( version 2 ).  We purchased that code 1 
month back from ISO.
In the reference software the AAC decoder is available along with all 
its tools within the following directory structure: 
 /audio/natural/rewrite/mp4AudVm
Now when I try to pass the interim conformance streams available from 
the FhG, I find them to be buggy !!!
For Example:
Bitstream number al03_44.wav is a reference wave files with a single 
channel ( channel 0 ) .
al03_44.mp4 is its corresposing reference encoded stream.
When I pass al03_44.mp4 through the reference decoder available from the 
MPEG ( ISO/IEC), I get an output wave file which has two channels ( 
channel 0 and channel 1) !!! This is just one of the many examples that 
I can give.
Now obviously this means that I cannot establish the conformance test 
criterion for the generated .wav output with respect to the reference 
.wav file
Even more interestingly, FhG seems to have come up with their own series 
of AL files starting from al14_*.* to al19_*.*
None of these files find a mention in the MPEG-4, Part 4, Conformance 
Testing document.
If what I have written above makes sense then it is really a catch-22 
situation. The MPEG-4 AAC Decoder cannot be validated until some body ( 
hopefully ISO ) comes up with a set of correct conformance test streams.
What I would really like to know is:  Is this a genuine problem ?  Or am 
I doing something terribly wrong ....
Thanks,
Umang Garg
NeoMagic Design Center
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