[M4IF Technotes] Re-3: MPEG-4 AAC-LC: Buggy Conformance Streams
Ralph Sperschneider
sps iis.fhg.de
Fri Jun 27 19:43:20 EDT 2003
Dear Umang,
the memberships of MPEG and M4IF are separate of each other. To become an MPEG
member you have to be nominated by your national body that is member of ISO to
join the work of ISO/IEC JTC 1/SC29/WG11. Check out
http://www.itscj.ipsj.or.jp/sc29/29w2po.htm to find the appropriate
standardization organization for your country.
Rob, please correct me if this is not fully correct. Maybe M4IF has already
appropriate inforation on its FAQ.
Best regards,
Ralph
Umang Garg wrote:
> 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 NeoMagic is very interested in updating the outdated MPEG-4 reference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:[email protected]/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
>>
>
>
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--
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/
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