Am 20.10.2013 18:08, schrieb Paul LeoNerd Evans:
On Sun, 20 Oct 2013 07:25:23 +0100
Tanu Kaskinen <[email protected]> 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
speakers.
This latency is occurring entirely with the tunnel receiver in my
laptop, and not mpd.
Interesting find. That indeed proves pulseaudio at the receiving end
accumulates latency. I have always felt it must be that way because the
progressbars of all media players I have tried correspond to where the
app is at decoding (and not what the speaker output).
I wonder if it's really in the tunnel module or somewhere deeper. I also
wonder if this works differently with the rewritten tunnel module (this
year's GSoC brought it, it's in git master but not released yet).
Best regards
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