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

[Alexander E. Patrakov]

вс, 5 мая 2019 г. в 22:58, Georg Chini <georg at chini.tk>:
>
> On 05.05.19 18:41, Alexander E. Patrakov wrote:
> > 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        detects that it is no longer applicable.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?
> >
> The significant difference was the removal of max_latency and
> the change of bool disable_rewind to int max_rewind. I need the
> error codes for handling message replies, that's why I added
> them. We should not need any other error reporting I think.

Then OK on the "significant" difference, and no review on anything else.

-- 
Alexander E. Patrakov