[Mp4-tech] AAC header in MP4 file format

[S. R. Quackenbush]

Vinayaka,
If you pick up the Apple MPEG-4 File format tools, it contains an example of
how to encode AAC in an MPEG-4 File. It clearly shows that at the Systems
level, the File contains signalling for
- mpeg-4 audio
-mpeg-4 audio profile and level
-mpeg-4 audioObjectType (e.g. AAC-LC)
-decoderSpecificInfo
The decoderSpecificInfo contains everything you need to instantiate a
decoder, and in fact is virtually identical to what MPEG-2 AAC defines as an
ADIF header. As a result, the MPEG-4 AccessUnits can be a series of MPEG-4
AAC Raw Data Blocks. Taken together, the MPEG-4 file has information
equivalent to an MPEG-2 AAC file with ADIF header, although the MPEG-4 File
Format is much nicer, in that it is iherently packet-oriented
Best,
Schuyler
---
Dr. Schuyler Quackenbush, Audio Research Labs
336 Park Ave, Suite 200,  Scotch Plains, NJ 07076
office: 908 490 0700      srq audioresearchlabs.com
mobile: 908 612 9423
fax:    908 842 9151      www.audioresearchlabs.com
  -----Original Message-----
  From: mp4-tech-bounces lists.mpegif.org
[mailto:mp4-tech-bounces lists.mpegif.org]On Behalf Of Vinayaka Hegde
  Sent: Wednesday, August 06, 2023 10:20 AM
  To: 'Mody, Mihir'; 'bharat nihalani'; mp4-tech lists.mpegif.org
  Subject: RE: [Mp4-tech] AAC header in MP4 file format
  Hi,
  I think Mihir is right. But how can we identify input stream in RAW form
is AAC or not? If decoder is know that, endoer is sending RAW form then only
we can procede with decoding.
  If decoder is not aware of the input bitstream type and some encoder sends
RAW form data to decoder. Is this possible?. If yes, How decoder identify
that input is AAC RAW form? Is it mandatory to have MP4 header or
MP2(ADIF/ADTS) header?
  Regards
  Vinayaka
    -----Original Message-----
    From: Mody, Mihir [mailto:mihir ti.com]
    Sent: Wednesday, August 06, 2023 7:26 PM
    To: 'bharat nihalani'; mp4-tech lists.mpegif.org
    Subject: RE: [Mp4-tech] AAC header in MP4 file format
    HI Bharat,
    The MP4 file contains AAC stream in RAW form. It is not possible to have
ADIF/ADTS header in AAC stream of MP4 file
    Regards,
    Mihir Mody,
    Multimedia Group,
    Texas Instruments Inc.,
    Bangalore, India,
    Email: mihir ti.com
    Phone :- +91-80-5099307
      -----Original Message-----
      From: bharat nihalani [mailto:ban611 yahoo.com]
      Sent: Wednesday, August 06, 2023 6:56 PM
      To: mp4-tech lists.mpegif.org
      Subject: [Mp4-tech] AAC header in MP4 file format
      Hi All,
      What kind of header can a MP4 file have in case of AAC?
      1) ADIF,
      2) ADTS, or
      3) RAW.
      I found with the MP4 file format streams that I have, that the AAC
stream was RAW, i.e. without ADIF or ADTS header in it. But is it possible
to have ADIF or ADTS header present in the MP4 file in case of AAC stream?
      Please clarify on this.
      Regards,
      Bharat
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