[M4IF Technotes] Re: Question on AAC object type

[Ralph Sperschneider]

Dear Anil,
there is unfortunately no such thing as a newsletter. The only possibly way I am 
aware of is to stay tuned to what is going on during the MPEG meetings. This can 
be done by participation, by screening the output documents of each meeting and 
in joining the interested ad-hoc groups.
All published standards are available here: 
http://www.iso.org/iso/en/CatalogueListPage.CatalogueList (for MPEG-4, just type 
the standard number 14496). Non-publicated standards are only available as 
meeting output documents, thus only available to MPEG members.
Hope this helps,
Ralph
Anil Kumar wrote:
> Hi Ralph, All,
> 	Regarding my previous question, most of my doubts were clarified thanks 
 > to Mr. Hans-Jürgen who pointed me to the audiocoding.com's wiki... apparently,
 > the ADTS header format was changed a little in Dec 2002 (according to the
 > wiki). However, I have one question... how do i keep track of such changes??
 > being an ISO member, is there any way we can get a newsletter or something
 > which intimates us of all these changes?? where can I find the latest
 > corrigendums/ammendments of ISO??
> 
> Thanks,
> Anil
> 
> -----Original Message-----
> From: Ralph Sperschneider [mailto:sps   iis.fhg.de]
> Sent: Friday, June 27, 2023 12:24 AM
> To: Hans-Juergen Bardenhagen
> Cc: technotes   lists.m4if.org
> Subject: [M4IF Technotes] Re: Question on AAC object type
> 
> 
> 
> 
> Hans-Juergen Bardenhagen wrote:
> 
> 
>>On Wednesday, 25.06.03, 10:56 Anil wrote:
>>
>>
>>
>>>1. Can I get an ADTS or ADIF as the transport layer for an MPEG-4
>>>stream?? (i guess it is yes, but just to confirm).
>>
>>
>>Not quite, because ADTS and ADIF are the header types of an AAC file  
>>(not a "transport layer" in the usual sense like e.g. HTTP or RTSP) that  
>>has not been multiplexed to a MP4 container yet. Inside this container  
>>the raw AAC bitstream does not have any headers anymore, because these  
>>informations (MPEG-x version, bitrate etc.) are handled by the MP4 file  
>>header then.
> 
> 
> Maby some more information:
> - adts ( audio data transport stream ) is intended for transport. It was 
> originally considered as become a "layer 4" (beside layer[123] as specified in 
> ISO/IEC13818-3).
> - adif ( audio data interchange format ) is intended for storage (it has just 
> one header at the beginning, followed by the raw_data_stream())
> 
> Both formats are specified in MPEG-2 and MPEG-4. There are some extensions in 
> MPEG-4 to allow the signalling of AAC LTP in addition to AAC Main, AAC LC, AAC 
> SSR and to distinguish between MPEG-2 and MPEG-4. However, these are AAC 
> specific formats.
> 
> For MPEG-4 Audio transport it is recommended to use LOAS/LATM (low overhead 
> audio stream, low overhead audio transport multiplex).
> 
> All these formats are specified in ISO/IEC14496-3.
> 
> Best regards,
> 
> Ralph
> 
> 
>>>2. What is the object type index for AAC LC in case of MPEG-2 and
>>>MPEG-4. Does this change depending on the transport layer(ADTS or ADIF
>>>or GA). 3. How do I distinguish b/w MPEG-2 and MPEG-4 in case of ADIF/
>>>ADTS (Is it the bitstream_type and adts_id) 4. Where can I get a
>>>complete documentation of all these things??
>>
>>
>>A short overview of the ADTS (and ADIF) header structure is available in  
>>the Wiki of Audiocoding.com:
>>
>>http://www.audiocoding.com/wiki/index.php?page=ADTS
>>
>>If you need more informations than this, you can download the  
>>specifications of MPEG-2 and/or MPEG-4 AAC from the MPEG homepage or the  
>>MPEG Audio Subgroup (links are mentioned in the Wiki, too). This also  
>>refers to the question of the MP4 file format, by the way.
>>
>>ZZee ya, Hans-Jürgen
>>
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> 
> 

-- 
Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
FhG IIS                         | Fax:   +49 9131 776 398
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