This question relates to two bits in ADTS header called ObjectType.

Are IDs for ObjectTypes equal for MPEG-2 and MPEG-4 AAC?

I see that MPEG-2 has ObjectType defined as:
MAIN = 0
LC = 1
...

and MPEG-4 defines ObjectType as:
NULL 0
AAC main 1
AAC LC 2
...


14496-3:2001, page 78 says:
"The interpretation of this bitstream element depends on the value of the ID bit. If ID is equal to ‘1’ this field holds the same information as the profile field in the ADTS stream defined in ISO/IEC 13818-7. If ID is equal to ‘0’ this element denotes the MPEG-4 Audio Object Type according to the table defined in subclause 5.1.1."

FAAD gives me the same ObjectType info, no matter if my ID is MPEG2 or MPEG4. Isn't this contradictory to the standard?

Daniel

In ADTS the object types are encoded 0 based. In MPEG-2 AAC (13818-7) the profiles are also defined 0 based, so the value read from the ADTS header matches the profile value. In MPEG-4 AAC (14496-3) the object type values are 1 based, therefore to get the object type value from the ADTS header value you have to do +1 on the value from the ADTS header.
FAAD2 internally only uses object type values, no matter if the file is MPEG-2 or MPEG-4 AAC.

Menno

You are looking at this form DEcoder side. Looking from the ENcoder side, you are saying that no metter MPEG-2 or MPEG-4, bitstream should always say 0 for MAIN and 1 for LC?