[pulseaudio-discuss] Understanding esound latency issues (was Re: pulseaudio automatic startup)

[Colin Guthrie]

Lennart Poettering wrote:
>> Also (completly OT now but as I may have your attention ;) when I use
>> the latest mplayer svn pulse code, when I use -ao esd (pointless I know)
>> I see two connections in paman Clients tab... one is a standard named
>> "EsounD client..." and the other is simply "MPlayer" (same as appears
>> for a -ao pulse). 
> 
> the named one is the one that actually streams audio. The other is
> used for vol control.

Cool :)

>> mplayer + esd has a fairly high latency FWIW, audio
>> and video appear out of sink for me and just playing a simple mp3 is
>> slower to start than with -ao pulse too. Just thought I'd mention it
>> (not really an important issue IMO but the same latency may affect other
>> apps where no specific pulse interface exists - certainly users have
>> reported that to me - so if you have any thoughts please share them :)).
> 
> esd provides no time synchronization info whatsoever, and this is
> absolutely not suitable for getting lip sync video.

Thanks for the info. I've done some tests here with interesting results.
If you've any insight here it would be useful.

I know esd is evil, but I just want to try and understand why this is
happening. I've tried with both pulse and the real esd:

When playing a 48kHz file, mplayer -ao esd will resample to 44.1kHz
before giving it to the audio layer. This results in bad lip sync with
esd and noticibly worse sync with pulse.

When playing a 44.1kHz file mplayer -ao esd will just pass the audio
straight to the audio layer. This results in bad lip sync with esd
(comparable to the above test) and *better* sync with pulse! (this is
probably due to the fact that the latency reported by mplayer esd is
actually higher than with pulse which is nice!).

So the question is, why does the extra resampling by mplayer cause worse
performance with pulse than with esd?

Col.