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

[Alexander E. Patrakov]

вс, 5 мая 2019 г. в 01:41, Georg Chini <georg at chini.tk>:
>
> On 04.05.19 20:54, Alexander E. Patrakov wrote:
> > 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       detects that it is no longer applicable.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.
> > OK.
> >
> >> 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.
> >
> Just finished the next version. Does this look OK to you now?

I think that the only significant difference is the addition of error
codes. I cannot comment on them with any authority, but the majority
do not seem applicable to filters. Probably we need some mechanism
that allows arbitrary error strings to be logged?

-- 
Alexander E. Patrakov