[pulseaudio-discuss] Transporting sound from 'mpd' server to laptop

Paul LeoNerd Evans leonerd at leonerd.org.uk
Sun Oct 20 18:08:45 CEST 2013

On Sun, 20 Oct 2013 07:25:23 +0100
Tanu Kaskinen <tanu.kaskinen at linux.intel.com> wrote:

> Latency can only increase only if there is some buffer that is
> growing. module-tunnel doesn't have such buffer. It sounds like MPD
> is working so that it writes at a constant pace to an internal
> buffer, and reads from the buffer at the rate that PulseAudio asks
> for more data. If network glitches occur, PulseAudio will ask less
> often, so MPD's buffer will get larger and larger. If this
> speculation is true, then MPD should be fixed. It should define some
> maximum size for the buffer. 30 seconds is silly. And if you're
> playing local files, this whole problem shouldn't exist, because MPD
> should decode the files at the rate PulseAudio is consuming the data,
> not at a constant wall-clock rate.

In fact, I have just used tcpdump to prove this isn't the case.

Because the TCP tunnel contains pure uncompressed PCM audio, a tcpdump
with hexdump of the raw TCP segments contains pure zeroes during
silence. With mpd paused, I see lots of zeroes go by.

The /moment/ I unpause mpd, those zeros turn into varying numbers,
containing real audio data. Yet my speakers remain silent... a number
of seconds afterwards, sound now comes out. So then I hit pause.
Instantly, those numbers in tcpdump are all zeroes again, but yet it
takes a number of seconds for the sound to stop coming out of the

This latency is occurring entirely with the tunnel receiver in my
laptop, and not mpd.

Paul "LeoNerd" Evans

leonerd at leonerd.org.uk
ICQ# 4135350       |  Registered Linux# 179460
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