[pulseaudio-discuss] [WIP] Passthrough support

[Arun Raghavan]

On Tue, 2011-03-15 at 17:36 -0500, pl bossart wrote:
> > I pushed your change along with a fix for the assert you saw to my tree
> > as well.
> 
> I tested the latest batch of patches with AC3/SPDIF this time. Works
> well in general, however I found some interesting points:
> - in Rhythmbox, the passthrough mode is only enabled if the first file
> of playlist is compressed. If you start with PCM/WAV, it always uses
> the PCM mode.

Are you using the crossfading backend? If yes, that won't work since
they create their own pipeline with a volume element in between to do
the crossfades.

With the non-crossfading backend, I see it setting up an MP3 stream when
it can and PCM when it can't.

> - in Totem, the passthrough mode works when the visual effects are
> disabled. I see a nice DD on my receiver...However the playback stops
> if you play with the volume slider. I get a pop-up error window saying
> 'an error occurred: pa_stream_set_sink_input_volume(): invalid
> argument'

Ah, I hadn't tried this out. We should be handling this more gracefully
right now - will put this on my TODO list.

> On a related note, maybe we want to change the approach to volume
> control. Depending on the sink, there might be ways of using
> side/in-band channels to send volume control information to the
> decoder. It's going to be protocol-specific. So maybe we need to
> provide the client with an information coming from the sink on whether
> volume control is actually supported or not.

Tanu's independently working on flags and notifications for signalling
when a sink-input (and sink, I believe) volume control is
readable/writeable. We're aiming to have this in 1.0 as well, so we
should end up piggybacking on his work for passthrough streams/sinks as
well.

-- Arun