[pulseaudio-discuss] Does SBC support dynamically changing bit rates and frame lengths?

[Burkhard Stubert]

2010/1/5 pl bossart <bossart.nospam at gmail.com>

> >>> > So, my question is: Does pulseaudio's SBC implementation support
> >>> > dynamically
> >>> > changing bit rates and frame lengths? If so, how and where?
> >>>
> >>> No, we don't support this right now.
> >>>
> >>> We probably should though. Please file a bug in the BTS so that we
> >>> don't forget about this. Even better: prepare a patch ;-)
> >>>
> >>
> >> Thanks for the info. I'll certainly file a bug report. And, I might
> actually
> >> try to prepare a patch, although I might need some help ;-)
> >>
> >
> > The current SBC implementation we have is just a copy of bluez's
> > implementation, so you should bring this up on the linux-bluetooth ML.
>

Thanks, Joao. I have noticed the code duplication already and will also take
this up with the Bluez guys.


> The bitpool parameter can in theory be changed at each frame, however
> the block size and number of subbands need to say fixed (there's a
> history buffer).
> So yes you can change the bitrate/bitpool but you cannot modify the
> size of the PCM provided as input to the encoder.
> - Pierre
>

 Pierre, what do you mean by the size of the PCM? Do you mean the frame
length? If so, I am confused, because the frame length explicitly depends on
the bitpool parameter. So, the frame length will change.

Moreover, I think that's the whole idea of an adaptive encoding. SBC
encoding masks sounds that are not audible to the human ear because they are
overshadowed by other sounds. Depending on how much the encoder can mask the
frame will be smaller or bigger. My understanding might be wrong. So, please
correct me.

Thanks,
Burkhard
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