[M4IF Technotes] Re-2: MPEG-4 AAC-LC: Buggy Conformance Streams

[Umang Garg]

Dear Ralph and other technotes members - Hello,
Thank you, for your inputs. They are very helpful.
NeoMagic Corporation is a 'full member' of the MPEG-4 Industry Forum. 
 You can find our name on  membership list of the MP4IF given at the 
following url:
 http://www.m4if.org/membercompanies.php?PHPSESSID=1d3dab78ae73103faf76ca1b8b7f7763
NeoMagic is very interested in updating the outdated MPEG-4 reference 
code that was shipped by ISO.  What should we do to facilitate that 
objective ?
Is the membership of the MP4IF a sufficient condition to get the weekly 
snapshots of the latest audio reference code ( along with a fully 
working version ! )  ?
If yes, from where can I obtain the latest release ?
OR, is it necessary to become a member of the MPEG-4 committee in order 
to get those regular updates ( along with a fully working version ! ) ? 
If yes, how can we take that initiative forward ?
I look forward to inputs on this matter.
Best Regards,
Umang Garg
NeoMagic Corporation
Ralph Sperschneider wrote:
> Umang Garg wrote:
>
>> Dear Members, Hello,
>>
>>
>> I understand that the MPEG-4 AAC-LC conformance streams are available 
>> at the following FTP site:
>>
>> ftp://mpaudconf:adif2mp4@ftp.iis.fhg.de/mpeg4audio-conformance
>>
>> I currently have with me an ISO provided 'reference software' that 
>> contains the MPEG-4 AAC Decoder ( version 2 ).  We purchased that 
>> code 1 month back from ISO.
>>
>> In the reference software the AAC decoder is available along with all 
>> its tools within the following directory structure: 
>>  /audio/natural/rewrite/mp4AudVm
>>
>>
>> Now when I try to pass the interim conformance streams available from 
>> the FhG, I find them to be buggy !!!
>>
>>
>> For Example:
>>
>> Bitstream number al03_44.wav is a reference wave files with a single 
>> channel ( channel 0 ) .
>>
>> al03_44.mp4 is its corresposing reference encoded stream.
>>
>> When I pass al03_44.mp4 through the reference decoder available from 
>> the MPEG ( ISO/IEC), I get an output wave file which has two channels 
>> ( channel 0 and channel 1) !!! This is just one of the many examples 
>> that I can give.
>>
>>
>> Now obviously this means that I cannot establish the conformance test 
>> criterion for the generated .wav output with respect to the reference 
>> .wav file
>>
>>
>> Even more interestingly, FhG seems to have come up with their own 
>> series of AL files starting from al14_*.* to al19_*.*
>>
>> None of these files find a mention in the MPEG-4, Part 4, Conformance 
>> Testing document.
>>
>> If what I have written above makes sense then it is really a catch-22 
>> situation. The MPEG-4 AAC Decoder cannot be validated until some body 
>> ( hopefully ISO ) comes up with a set of correct conformance test 
>> streams.
>>
>> What I would really like to know is:  Is this a genuine problem ?  Or 
>> am I doing something terribly wrong ....
>>
>> Thanks,
>>
>> Umang Garg
>> NeoMagic Design Center
>>
>
> Dear Umang,
>
> please find below some comments with regard to your observations.
>
> reference software:
> -------------------
> I can confirm the behavior you describe (just downloaded the code from 
> http://www.iso.ch/iso/en/ittf/PubliclyAvailableStandards/ISO_IEC_14496-5_2001_Software_Reference/ 
> and compiled it), but have no idea why that decoder generates an 
> output file with two channels while decoding al03_44.mp4. As long as 
> you only like to deal with AAC (Main, LC, SSR or LTP), you might 
> alternatively use the multichannel AAC decoder (available under 
> /audio/natural/refSoft/mp4mcDec). I checked this decoder as well and 
> it produced just one channel. Thus, the sequence is correct, but the 
> rewrite decoder is malfunctioning.
>
> Anyway, you should consider that the software you purchased from ISO 
> is outdated (it is about 2 years old). It always takes ISO a 
> significant time to publish any new standard piece. So one reason to 
> become an MPEG member might be to have access to weekly snapshots of 
> the MPEG-4 audio reference software. With the current rewrite decoder 
> I get just one channel if I decode al03_44.mp4 (hence, this bug has 
> been fixed meanwhile ;-)).
>
> conformance test sequences:
> ---------------------------
> All al* conformance test sequences on our server (except of al15, 
> which is currently in the process to be updated) have successfully 
> been cross-checked. All of them can be decoded with the multichannel 
> decoder. The rewrite decoder does not yet support DRC and multichannel 
> decoding (just mono and stereo).
>
> It is not that FhG has come up with their own series of test 
> sequences. The sequences on our server are even not the property of 
> FhG. We just support the work of MPEG on a complimentary basis in 
> hosting these sequences and furthermore in providing access to them 
> even for non-MPEG members.
>
> * al14, al15, al16 and al17 have been added by means of ISO/IEC
>   14496-4:2000/Cor.2 (unfortunately not yet published):
>   - al14, al15 and al16 test DRC (previously there where only 
> sequences for AAC
>     Main available to test DRC).
>   - al17 tests the evaluation of the element_instance_tag (it provides 
> two SCEs,
>     where the order of them switches from frame to frame)
> * al09 and al10 have been renamed to al18 and al19 to avoid name 
> conflicts with
>   MPEG-2 AAC conformance test sequences.
>
> All these issues are covered by the second edition of ISO/IEC14496-3, 
> which is also not yet published (again, it is out of MPEG´s hands, but 
> needs to be processed by ITTF).
>
> I hope this helps for the moment. I know that its not always easy to 
> understand what is going on in MPEG, especially since it takes 
> occasionally a longer time for ISO/ITTF to publish new standards. 
> However, MPEG members are usually nice and answer any questions 
> related to their standardization work, as long as they are asked in a 
> friendly manner ;-).
>
> Best regards,
>
> Ralph
>