Arch Linux

RankoKohime

Member

Registered: 2014-01-08

Posts: 87

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Creeping latency with pacat

I have a streaming audio setup with a Windows 7 computer, which runs Linco and Netcat to transfer the audio there to my Arch system.  I originally set this up when running Mint 16, where it didn't have this issue.  Both computers are connected to the same Gigabit switch, so there is ample bandwidth available for this.

I execute this command on my Arch system:

netcat -lvp 6000|pacat --playback --latency-msec=30

What occurs is that the latency is invisible to the eye (say, when playing a game on the Windows computer, the sounds appear timed correctly) initially, but over time the latency will increase, until after 2 hours, I'm seeing/hearing almost a full second of latency.

Any ideas why this might be occurring?  Regression in Pulse, perhaps?

emeres

Member

Registered: 2013-10-08

Posts: 1,570

Re: Creeping latency with pacat

 Seems like expected behaviour, pulseaudio appears not to drop packages, so they stack up, or resynchronize. I never used that kind of a setup, so I base this on my experience gathered elsewhere. Take a look at this module.

module-combine-sink

Since 1.0 (prior to 1.0 this same module was available with name "module-combine"). This combines two or more sinks into one. A new virtual sink is allocated. All data written to it is forwarded to all connected sinks. In equidistant intervals the sample rates of the output sinks is recalculated: i.e. even when the sinks' crystals deviate (which is normally the case) output appears synchronously to the human ear. The resampling required for this may be very CPU intensive.

 As for the solution, is do not see any relevant parameters in the documentation. However one way to determine the difference between your current setup and the one using Mint or others, would be to compare PAs configuration and systems modules, their parameters to be exact.
 A workaround would be to periodically restart the stream on the Windows machine.