Re: [codec] #8: Sample rates?

["Christian Hoene" <[e-mail]>]

>
>#8: Sample rates?
>------------------------------------+---------------------------------------
> Reporter:  hoene@…                 |       Owner:
>     Type:  enhancement             |      Status:  new
> Priority:  minor                   |   Milestone:
>Component:  requirements            |     Version:
> Severity:  Active WG Document      |    Keywords:
>------------------------------------+---------------------------------------
>
>Comment(by kpfleming@…):
>
> If our goal is to use RTP AVP/SAVP/AVPF/SAVPF profiles for transport (as
> seems likely), then differences in sample rates between stream offers must
> be listed separately in the SDP. Whether they have a different codec
> 'name' in the SDP or not seems less important, because the combination of
> the codec name and sample rate is required to uniquely identify the format
> in any case. Note that this is *sample rate*, and not bitstream rate.

No, please not. Please keep the interface to the codec as simple as possible!
 
In addition, one must consider the following requirements:

1) First, the sample rate MUST be changed dynamically to cope with varying transmission bandwidths.
2) Typically, sound cards do not allow changes of the sample rate on the fly. 
3) Thus, the codec SHOULD have an internal sampling rate conversion.

I would recommend to use only one nominal sampling rate (e.g. the sampling rate of the sound card) and let the codec do the conversion between the actually used and predefined.

It might be useful to state that it is not recommended to use 44100 Hz, because the conversion to 16kHz and 32kHz is computational more demanding than 48kHz and requires more power/time.

With best regards,

 Christian