Re: PulseAudio and Phonon?

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Re: PulseAudio and Phonon?
by Kevin Kofler on Sunday 04/Nov/2007, @18:34

The callgraph actually looks like:
Phonon -> xine-lib/GStreamer -> PulseAudio -> ALSA

Xine-lib or GStreamer are used to implement the Phonon backend. (KDE 4.0 will come with Phonon-Xine. As far as I know, Trolltech is working on a GStreamer backend for Phonon.) They handle decoding using a plugin framework, then hand off the decoded stream to either the hardware or a sound server such as PulseAudio through an output plugin.

PulseAudio can also work as an ALSA plugin, in which case the applications think they're talking to a native ALSA device, but what they get is not a hardware device, but a connection to PulseAudio. This is very similar to how dmix works. In a Phonon context, this makes the callgraph look like this:
Phonon -> xine-lib/GStreamer -> ALSA (PulseAudio plugin) -> PulseAudio -> ALSA (hardware device)
I've read reports that xine-lib's native PulseAudio output plugin currently isn't very stable, so with xine-lib using the PulseAudio ALSA plugin is more reliable. Fixing this in xine-lib is on the PulseAudio TODO list, but in a KDE 4 context it might become moot with the Trolltech-backed Phonon-GStreamer anyway.

Related Links

·   Articles on KDE Official News
·   Also by Kevin Kofler
·   Contact author

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