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

[Ralph Sperschneider]

Marc Jaeckle wrote:
>> The bad aspect of PCU and RCU is that they are imprecise. Max number of
>> instantiations, channels, and sampling rates would be much easier to
>> interpret, but would result in less flexability.
> 
> That's basically where my problem lies. I don't understand how the 
> sampling rate influences the complexity (and therefore the RCU and PCU) 
> of an audio object.  For some objects (e.g. AAC LQ or CELP) the PCU 
> seems to be proportional to the  sampling rate but what about the RCU? 
> Is there a way to calculate the RCU and PCU for an audio object at a 
> given sampling rate or does the standard only give me the PCU and RCU 
> for a single specific sampling rate for each audio object (like in the 
> table "complexity estimates for the different audio object types")? Or 
> to put it more general: How are the RCU and PCU calculated?

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.
Ralph
>> ... but would result in less flexability.
> 
> I'm aware of the better flexibility that is achieved by describing 
> levels with PCU and RCU that's why I was wondering why not all levels 
> are defined by PCU and RCU. The first three levels of the Scalable 
> Profile are defined by configuration for example and the Speech profile 
> defines levels in terms of the max number of objects. I find this a 
> little bit confusing and inconsitent. Was there a certain reason for 
> this? (Well I guess there was a reason but what kind of reason :-)
> 
> Gruß
> Marc
> 
> 
> _______________________________________________
> Mp4-tech mailing list
> Mp4-tech lists.mpegif.org
> http://lists.mpegif.org/mailman/listinfo/mp4-tech

-- 
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/