AAC-HE Decoder problem with LATM complaint aac streams

Hi Sreenu,

This version of AAC decoder doesn't support LATM streams. It supports ADTS, ADIF and raw streams.

Ram

Hi Ram,

Thanks for your reply.

Could you plz let me know which aac decoder version supports MPEG4 PART7 AAC LATM/LOAM complaint streams.

Regards,

Sreeni.

Hi Sreeni,

v01.30.10.000  AAC-HE decoder supports LATM/LOAS streams.

Ram

Hi Ram,

I could only get latest version as v01.30.03.00 from TI site http://software-dl.ti.com/dsps/dsps_public_sw/codecs/C64XPlus_Audio/index_FDS.html 

and build date looks bit old  "Build date: 07012010" .

Could you plz help me where can I find latest version.

And it would be great if you could help on start code prefix or Sync word (Ex: 12 field 0xFFF) and header format for the AAC LATM streams.

What I could get from web is as below,

"ADTS
Unlike the ADIF header, ADTS (Audio Data Transport Stream) headers are present before each AAC raw_data_block or block of 2 to 4 raw_data_blocks. Until the MPEG revision from Dec 2002 for MPEG-4 AAC ADTS headers, this was basically the same as a MP3 header, except that the emphasis field was not present for MPEG-2 AAC, only for MPEG-4 AAC.
Now the emphasis field (2 bits) has been abandoned completely, and thus MPEG-4 and MPEG-2 AAC ADTS headers are exactly the same except for the Object Type ID flag (MPEG-2 or MPEG-4). See also the Wiki page about MP4, because this is important when extracting MPEG-2 AAC files from a MP4 container with mp4creator or creating MP4 files from PsyTEL AAC encodings with this tool.

The ADTS header has the following fields:
Field name Field size in bits Comment
ADTS Fixed header: these don't change from frame to frame
syncword 12 always: '111111111111'
ID 1 0: MPEG-4, 1: MPEG-2
layer 2 always: '00'
protection_absent 1
profile 2
sampling_frequency_index 4
private_bit 1
channel_configuration 3
original/copy 1
home 1
ADTS Variable header: these can change from frame to frame
copyright_identification_bit 1
copyright_identification_start 1
aac_frame_length 13 length of the frame including header (in bytes)
adts_buffer_fullness 11 0x7FF indicates VBR
no_raw_data_blocks_in_frame 2
ADTS Error check
crc_check 16 only if protection_absent == 0
After that come (no_raw_data_blocks_in_frame+1) raw_data_blocks.
Some elaborations:
profile
bits ID == 1 (MPEG-2 profile) ID == 0 (MPEG-4 Object type)
00 (0) Main profile AAC MAIN
01 (1) Low Complexity profile (LC) AAC LC
10 (2) Scalable Sample Rate profile (SSR) AAC SSR
11 (3) (reserved) AAC LTP ""

Is that the above header format will work for LATM streams as well?

 I am facing issue while capturing from TS and I might be missing the header so the captured file is not playing it on any players.

Regards,

Sreeni.

Hi Sreeni,

Syncword for LATM stream is 0x2b7(11 bits) and in bitstream you will see 0x56E(shifted by 1 bit). For the stream you have attached, it is at 0xC8 position.

Refer section 1.7 of http://jaadec.sourceforge.net/specs/ISO_14496-3_Audio-1_Overview.pdf

Ram

Hi Ram,

Thanks a lot!  for your valuable information.

Regards,

Sreeni.

Hi Ram,

Could you plz tell me where can can I find latest version as v01.30.10.00. I could not get the one from TI site.

Regards,

Sreeni.

Hi Sreeni,

This version of decoder is not available for public yet.  I will check with audio codec team.

RAm

Hi Ram,

Yes plz let me know that would help us!!

Regards,

Sreeni.