[Mp4-tech] Difficulties understanding MPEG-4 audio profiles andlevels

[S. R. Quackenbush]

Marc,
The good aspect of PCU and RCU is that it really focusses on processor
resources. At a given profile and level you can run any mix of audio tools
such that they don't exceed the profile and level RCU and PCU.
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.
Best,
Schuyler
---
Schuyler Quackenbush	Chair, MPEG Audio Subgroup
CEO, Audio Research Labs
336 Park Ave, Suite 200, Scotch Plains, NJ 07076
phone: 908 490 0700	srq audioresearchlabs.com
fax:   908 842 9151	www.audioresearchlabs.com
> -----Original Message-----
> From: mp4-tech-bounces lists.mpegif.org
> [mailto:mp4-tech-bounces lists.mpegif.org]On Behalf Of Marc Jaeckle
> Sent: Monday, August 25, 2023 4:02 PM
> To: MP4-Tech lists.mpegif.org
> Subject: [Mp4-tech] Difficulties understanding MPEG-4 audio profiles
> andlevels
>
>
> I'm having difficulties to understand which sampling rates and bit
> rates are allowed for a given profile @ level combination. The standard
> only seems to specify the maximum Processor Complexity Units (PCUs) and
> RAM Complexity Units (RCUs) for every level, the PCU and RCU number of
> every object type at 48kHz (in the case of AAC) and the types of
> objects allowed for a profile.
>
> What I don't understand is how the sampling rate and bit rate are
> related to the complexity (measured in RCU and PCU). For some object
> types the PCU seems to be proportional to the sampling rate but what
> about the others (e.g. CELP object types) and what about the RCU?
>
> ... and why are some levels defined by sampling rate while others are
> defined by complexity or the number of objects.
>
> Any help would be greatly appreciated :-)
> Gruß
> Marc
>
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