[pulseaudio-discuss] [PATCH 12/13] loopback: Validate the rate parameter

[Alexander E. Patrakov]

18.12.2015 13:04, Georg Chini wrote:
> On 18.12.2015 08:45, Alexander E. Patrakov wrote:
>> 18.12.2015 11:47, Georg Chini wrote:
>>> On 18.12.2015 06:49, Tanu Kaskinen wrote:
>>>>
>>>>
>>>> Making pa_sample_rate_valid() accept values above PA_RATE_MAX isn't
>>>> very nice, but I can see how it's better than the current behaviour,
>>>> which probably can cause the daemon to crash. Alexander mentioned in
>>>> IRC that he'd prefer doing the adaptive resampling inside module-
>>>> loopback rather than using pa_sink_input_set_rate(), and this change
>>>> demonstrates one good reason for that. I'm not asking you to implement
>>>> that change, but it certainly would be nice.
>>>>
>>>> --
>>>> Tanu
>>> Yes, doing it inside the module would really be a good idea. The
>>> main issue my controller is fighting against are the systematic
>>> errors introduced by changing the rate of the sink input. When
>>> you change the rate, the next latency report has an extremely
>>> high error.
>>> Can you point me to some code that implements resampling
>>> so that I have an example of what to do?
>>
>> Look at the ffmpeg resampler inside PulseAudio tree, it's the simplest
>> possible one. But I'd say that it's pointless to look at the code
>> without understanding the math behind all of that, so please look at
>> these links, too:
>>
>> https://en.wikipedia.org/wiki/Sinc_filter
>> https://ccrma.stanford.edu/~jos/resample/resample.pdf
>>
> I would first use the existing resamplers before trying to implement my
> own.
> So I was rather referring to the framework used in pulseaudio when using
> existing resamplers. If I ever write a specific resampler for the
> loopback module
> it could be integrated into the normal framework.

And that's exactly what I am against. Neither the normal framework nor 
any of the existing (even outside PulseAudio) non-GPL resamplers support 
sub-sample latency reporting. Please write your own resampler, that's 
what I meant on IRC. I know that in a similar email to you I also said 
"or treat the problem as unsolvable", this still stands, and Tanu's 
"would be nice" also allows that.

-- 
Alexander E. Patrakov