[winswitch] speaker-restart during video play in xpra 0.15

Antoine Martin antoine at nagafix.co.uk
Fri Jun 5 10:15:20 BST 2015

On 05/06/15 03:52, Jiang Qian wrote:
> Hi all,
> After making some minor adjustments to my configuration (clipboard and
> dpi, chiefly) 
Has anything changed in 0.15 with regards to DPI?
I am not aware of changes that should have affected it.
> I am settling happily to xpra 0.15 (both server and
> client, both on Ubuntu 14.04) They are connected over unencrypted raw
> tcp stream.
> I am puzzled by one behavior. I am forwarding sound, using the
> encoding Wavpak. (--speaker-code=wavepak) When I play an extended
> video clips, I got a large number of (about 2-3 in row, sometimes)
> re-starting speaker because of overrun.
> So far, aside from the fact that the audio is slight out of sync from
> the video, there seems to be no adverse consequences.
overruns are annoying but they should be harmless.
FYI: the delay with wavpack is the worst of all the codecs:
> I do confess I am puzzled because I thought because xpra 0.15 seperate
> audio to a separate process, the forwarding would be less prone to
> network jitters and the like.
That's true, but the problem with sound overruns is not necessarily
caused by network jitter.
With some codecs (wavpack and flac for example), we are getting the
sound data in larger chunks, which makes it much more likely that we hit
the buffer limits and get overruns.
0.16 will change the way we handle overruns to try to tune the buffer
size without having to restart the whole pipeline.
Minimizing this buffer will help in keeping the sound and video in sync.
> In addition, I am running over a high quality gigabit network, through
> which thousands of ping roundtrips return without a single lost packet
> and a nearly uniform roundtrip time of 0.25ms, so what *are* the
> network congestions or jitters that affect the sound stream? The video
> is far from saturating the bandwith, at merely 30-40MB/s when a
> straight file transfer can approach 80-90MB/s.
> If there is more debugging I could do, I will be happy to provide more
> information.
Until 0.16 is ready for testing, I would suggest not using wavpack,
which is just not very well suited for our use case.
Stick with mp3, flac or even just wav if you have bandwidth to spare.

> Thanks in advance.
> Regards
> Jiang
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