[M4IF Technotes] Re: Question on AAC object type
Ralph Sperschneider
sps iis.fhg.de
Wed Jul 2 11:53:17 EDT 2003
Dear Anil,
Anil Kumar wrote:
> Hi Ralph,
> Thanks for the info. I was going through the meeting output documents, and there seems to have been a significant change in the test sequences from the time I started working on AAC (1.5 yrs ago) and rightly so, as I understand, MPEG is a living thing!!.
That is indeed true.
> The doc w5373 (study on MPEG-2 AAC Conformance) written by you has a detailed description of all the MPEG-2 test cases. Is there any doc similar to this one, but on the MPEG-4 test cases??
Yes, the most recent MPEG-4 Conformance document is N5457.
> I also found a MPEG-2 reference softwere (refSoft_mpeg2aac_20030616.tgz) on the ftp://ftp.tnt.uni-hannover.de/incoming/cvs/ directory, but this code unfortunately doesn't work.
What exactly is not working? I am quite sure that this software works properly.
> Where can I find a reference MPEG-2 AAC decoder source (I think the MPEG-4 source is supposed to decode the MPEG-2 streams also, but it doesn't seem to recognize a .aac extension at all!).
This is since the aac extension doesn´t mean anything. AAC data are usually
stored into a container. This might be
- adif or mp4ff for storage
- adts or latm/loas for transmission
> Also, is there a latest doc collating all the significant changes that has happened so far on MPEG-2/4?
For MPEG-2 AAC, the latest documentation is N5374.
For MPEG-4 Audio, there is currently another merge activity going on to
integrate ISO/IEC14496-3:2001, ISO/IEC14496-3:2001/Cor.1:2002 (N4760) and
ISO/IEC 14496-3:2001 FDAM 1 (the new Extension toward Spectral Band Replication,
N5570) and you can expect an updated document after the next MPEG meeting.
> I could not find the CRC polynomial in the 13818-7 doc, but there seems to be test sequences to test this.
The CRC polynomial is reused from MPEG-1 Audio. It is originally specified in
ISO/IEC 11172-3 (MPEG-1 Audio), subclause 2.4.3.1 as G(X)=X16+X15+X2+1.
> I think most of my problems will be solved once I get hold of a reference software that can decode these sequences (Or am I wrong??)
The CRC derivation in the multichannel decoder (mp4audec_mc mp4mcDec) of the
MPEG-4 audio reference software works properly.
>
> Hoping for some inputs on these questions,
> Anil
Hope my comments help.
Best regards,
Ralph
PS: In the future, please avoid to ask similar questions several times in
different e-mails.
> -----Original Message-----
> From: Ralph Sperschneider [mailto:sps iis.fhg.de]
> Sent: Friday, June 27, 2023 10:22 PM
> To: Anil Kumar
> Cc: technotes lists.m4if.org
> Subject: Re: Question on AAC object type
>
>
> 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
>>>
>>>_______________________________________________
>>>Technotes mailing list
>>>Technotes lists.m4if.org
>>>http://lists.m4if.org/mailman/listinfo/technotes
>>
>>
>
--
Dipl.-Ing. Ralph Sperschneider | Phone: +49 9131 776 344
FhG IIS | Fax: +49 9131 776 398
Am Wolfsmantel 33 | mailto:sps iis.fhg.de
D 91058 Erlangen | http://www.iis.fhg.de/amm/
More information about the Mp4-tech
mailing list