[pulseaudio-discuss] Screen casting with PulseAudio

[Rémi Denis-Courmont]

On Tue, 18 Oct 2011 13:38:39 +0200, Michał Sawicz <michal at sawicz.net>
wrote:
> Dnia 2011-10-18, wto o godzinie 13:33 +0200, Rémi Denis-Courmont pisze:
>> Eh? The user doing the recording typically wants to hear the sound
>> while recording. So I don't see what null sink has to do here.
> As long as you only want to record your speakers, then just record the
> monitor of the output sink. The null / loopbacks can help if you want to
> record microphone, too.
> 
>> > Obviously that's not relevant to VLC itself, it's through 
>> > pactl/pacmd (sorry) and pavucontrol that you need to select the 
>> > appropriate recording source.
>> 
>> So that's not an answer to the problem. 
> Yes it is. VLC isn't the place to choose recording inputs. Volume
> control tools are the place to do so.

That's a different topic. But while this looks like a popular conception
among PulseAudio developers, I have to partly disagree.


Video applications need to provide a choice of video sources (webcams,
desktop capture...). For this, there is no video mixer applications. In
terms of usability, I would expect to choose the audio source at the same
time as the video source.

The "volume control" tool would have two problems:
- It only works after the record stream is started, so that the source
output exists. For recording purpose, you'd want to select the source
before you start the recording.
- It has poor usability. The user would have to configure the application,
including all parameters except the audio source and amplification. For
those, it would have to open a separate application.

So I think it's fair for recording/streaming applications to act as their
own "volume control tool". Of course, they should play good citizens with
the other volume control tool(s) in the system, and in particular not
actively fight changes initiated by the PulseAudio daemon or another
PulseAudio client.


And in fact, the same applies partly to output (playback/streaming). Any
reasonable media player has a volume control, and possibly a balance and an
output devices choice list. So long as it lets PulseAudio set the initial
values and does not prevent other tools from moving or tuning the sink
input, I must say I don't see a problem.

-- 
Rémi Denis-Courmont
http://www.remlab.net/