Audio output device errors should be recoverable

[Dustin Spicuzza]

Currently, certain types of audio output problems (such as removing a USB audio device during playback) cause errors to happen that currently Exaile cannot recover from. These problems should be addressed.

[Dustin Spicuzza (dustin-virtualroadside)]

If you eject a CD when playing it, this problem occurs also. Will need to test that case once this is fixed.

[Johannes Sasongko (sjohannes)]

In Windows:

* Unplugging a USB soundcard causes playback to switch to my on-board soundcard. Disabling the on-board soundcard causes Exaile to try playing the next track, and the next, and the next....

* Unplugging a USB drive causes playback to stop with an error message (displayed on the info bar).

* Can't test with CD because the CD plugin is looking for dbus (we should make this optional). Although, on second thought, I can probably use the Files panel.

[Dustin Spicuzza (dustin-virtualroadside)]

Interesting. When unplugging a USB device, one of the Linux audiosinks exhibits the switching behavior, and the other doesn't. I think ALSA switches automatically, and PulseAudio just stops playback.

I think the main thing that the CD plugin provides via hal/udisks is autodetection of the CD contents. I believe gstreamer supports CD output on all supported platforms, but I'm not sure if it supports enumerating the contents of the CD. It would be cool if we could use GST to do this type of thing instead.

[Dustin Spicuzza (dustin-virtualroadside)]

To be more precise, CD playback using the ALSA sink, when you have multiple songs queued from the CD.

[Dustin Spicuzza (dustin-virtualroadside)]

Johannes, I just pushed a fix at r4577 that I believe fixes the root of the problem -- namely, that the mainbin isn't flushed out before the error recovery tries to use it again. Can you confirm that your Windows issues are fixed also? If so, I think we're ready for a 3.4 release.

[Dustin Spicuzza (dustin-virtualroadside)]

Tested fix on Windows 8 with a USB soundcard, looks like it works fine. It does have the odd problem of zooming through the playback instead, but you can still control it properly.