[Mp4-tech] [AAC Audio] [ADTS]

[Will Bolam]

hi all,
i've recently been looking at implementing an AAC decoder, and i now have
this working (based on the ISO reference code), i'm currently adding ADTS
support. i've got it working and decoding the test streams from here:
ftp://mpaudconf:adif2mp4@ftp.iis.fhg.de/g...io-conformance/ (the adts
streams are in the mpeg2 aac folder)
however i am unable to decode any of the various test streams we have from
customers. the test streams i have look like ADTS - they have the ADTS sync
word (12 1's) every so often in the file (including at the start), but the
rest of the ADTS header doesn't seem right - the layer field seems always to
be 2, when all specs i've seen say this must always be 0.
example header that doesn't work is:
1111 1111 1111 - syncword
1 - mpeg 2/4 flag
10 - layer
0 - protection absent
11 - profile obj type
0001 - sampling frequency index
0 - private bit
000 - channel config (Q. - is 0 valid for ADTS channel config? how else
would it be calculated?)
0000 - 4 copyright flags
0010 1000 1111 1 - frame length
1000 1010 101 - buffer fullness
01 - num raw data blocks
does anyone know whether that is or isn't a valid ADTS header? are there any
other audio file formats that use 12 1's as a sync word?
any help much appreciated!
regards,
will