[Mp4-tech] Re: Difficulties understanding MPEG-4 audio profilesandlevels

[Ralph Sperschneider]

Dear Marc, all,
Marc Jaeckle wrote:
>> We had the same problem while specifying the various conformance test 
>> sequuences to the individual levels. Hence, whe have drafted some 
>> formulas. Check out ISO/IEC 14496-3:2001/Cor 1:2002. You will find 
>> there formulas to calculate RCU and PCU for a wide range of AAC 
>> configurations.
> 
> 
> I had a look at the document but I couldn't figure out all the 
> abbreviations used in the formulas. Searching the standard for PCU_ref, 
> RCU_ref, fs_ref, #DepCouplingCh and #IndepCouplingCh didn't produce any 
> results. Can you possibly provide the terms they stand for or in the 
> case of PCU_ref, RCU_ref and fs_ref the place where I can find the 
> correspoding values (I'm guessing that those are the values from table 
> 1.3 "Complexity of Audio Object Types and SR conversion" but I'm not 
> really sure)?

* PCU_ref, RCU_ref and fs_ref are of course the values mentioned in Table 1.3.
* #DepCouplingCh and #IndepCouplingCh are the numbers of dependently and
   independently switched coupling channels.
> Actually I would be even more grateful for a short explanation of the 
> formulas/terms since I'm pretty(completely) new to MPEG-4 audio and 
> probably wouldn't be able to interpret the meaning of the terms without 
> reading most of the standard (which I should of course :-) unluckily 
> this is not an option at the moment).

RCU - derivation
----------------
* fs/fs_ref considers the linear complexity scaling by means of the actual
   sampling frequency
* dependently switched coupling channels don´t require an individual IMDCT, so
   the complexity factor is 0.3; for all other channels it is 1.
PCU derivation
--------------
* factors before the #xyzChannels are due to possible memory sharing
* the redeced increase of memory for channel pairs is due to memory sharing
   (note that the closing squared bracket in the RCU formula for CPE<2 has to be
   put before #CPE rather than after it)
Best regards, Ralph
-- 
Dipl.-Ing. Ralph Sperschneider  | Phone: +49 9131 776 344
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