[Mp4-tech] [MPEG-4 Audio] Size mismatch when AAC-LC test vector is passed through HE-AAC decoder

[Vora, Veenit]

Hello Everyone,
I am working on the HEAAC profile (AAC-LC + SBR) of the MPEG-4 standard. I am using the Reference Code for the decoder provided by ISO for this purpose. The version of the Reference Code is: ISO/IEC 14496-5:2001/Amd.6:2005. The decoder that I am using is located in the folder "mp4AudVm_Rewrite".
To test the conformance of the "AAC-LC" part of the decoder, I am passing a reference vector for the AAC-LC AOT that is given by ISO, through the HEAAC profile decoder. It generates an output file whose size is larger than the size of the corresponding reference wav file that is provided by ISO. On viewing the data of the two files, I find that the test data exactly matches the reference data after a certain number of bytes are offseted from the start of the test file. My queries are:
1. Why would the HE-AAC decoder generate a test output whose size is larger than the reference output, for the AAC-LC test vector. (the size is not exactly double so this eliminates the possibility of this happening due to SBR tool being enabled in the decoder ( since SBR operates at twice the sampling freq of AAC))?
2. How can I eliminate this offset being written by the HEAAC decoder. On removal of these offset bytes at the start of my test output, my test output would be bit-match with my reference output.
Thanking everyone in advance. Awaiting an early reply.
Regards,
Veenit Vora.
Patni Computer Systems Ltd.,
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Mumbai - 400096.
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