[pulseaudio-discuss] new module module-plugin-sink

Alexander E. Patrakov patrakov at gmail.com
Sat May 4 18:54:09 UTC 2019

сб, 4 мая 2019 г. в 20:25, Georg Chini <georg at chini.tk>:
> On 04.05.19 16:42, Alexander E. Patrakov wrote:
> > сб, 4 мая 2019 г. в 16:17, Georg Chini <georg at chini.tk>:
> >> Here is the new version of the header file, based on your feedback.
> >> The main changes are:
> >>
> >> - The create_filter() function now receives the channel maps for input
> >> and output.
> >> - The create_filter() function receives a kill_filter() function and a
> >> module pointer
> >>      which makes it possible for the filter to initiate unloading of the
> >> module if it
> >>      detects that it is no longer applicable.
> >> - An output_changed() function was added which communicates current sink
> >>     and port name to the filter, so that it can detect if the output has
> >> changed.
> >>
> >> Also I did a bit of cleanup and added a few more comments. Hope it looks
> >> better now.
> > It definitely looks better.
> >
> > I am still confused about disable_rewind and max_latency. Let's
> > suppose that someone wants to implement a rewindable filter. In this
> > case, they need to keep history, because PulseAudio can ask the filter
> > to rewind some samples. And, as it is not allowed to say "no", they
> > must keep enough history to satisfy any possible rewind request. But
> > some upper bound must exist. Do I understand correctly that
> > max_latency serves as such upper bound?
> >
> > Regarding the non-rewindable filters, we do need to limit the latency,
> > but I believe it is wrong for each individual filter to specify its
> > own value for such limit. It should be a global policy (the same value
> > for all non-rewindable sinks), and I don't see any reason for the
> > filter to be able to influence it.
> >
> > Therefore, I believe these two fields can be replaced by one,
> > max_rewind, which is the size of history, in samples, that the filter
> > is willing to keep. Zero means a non-rewindable filter.
> >
> That sounds like a good suggestion. I would however think
> that it is better if 0 means that the filter will rewind as far as
> PA wants it to. There may be filters that are stateless (like the
> trivial amplifier example). We could use -1 to disable rewinding.


> That would also mean to limit the latency to whatever the filter
> can rewind, correct? I would use the maximum of max_rewind
> and the default latency for non-rewindable filters as the
> max_latency value then, because I don't think it makes sense
> to set the maximum latency even smaller than for non-rewindable
> filters.

Makes sense.

> What do you think is reasonable for non-rewindable filters?
> 50 ms?

There were different opinions on that matter. 50 ms is indeed in a
range that I would agree to.

Alexander E. Patrakov

More information about the pulseaudio-discuss mailing list