[pulseaudio-discuss] long delay after "paplay -s somehost foo.wav"

[Lu Guanqun]

Hi,

On Wed, Aug 10, 2011 at 09:47:47PM +0800, Paul Fox wrote:
> colin wrote:
>  > 'Twas brillig, and Paul Fox at 08/08/11 15:21 did gyre and gimble:
>  ...
>  > > but this:
>  > >     paplay -s server one.wav
>  > >     paplay -s server two.wav
>  > > will result in a delay of over 2 seconds between "one" and "two". 
>  ...
>  > 
>  > This is likely related to the drain. In order to be 100% sure that the
>  > data is no longer needed (as it may be needed by rewind buffers) we have
>  > to wait.
>  > 
>  > There are a few bug reports about this kind of thing in e.g. the simple
>  > protocol, but I'm not sure we can solve it 100% in all cases.
> 
> thanks.  i found this: http://www.pulseaudio.org/ticket/866
> 
> it certainly sounds like a fix will be a long time coming.  it feels
> to me that there should be a way for a stream to be started with a
> different "contract", i.e., "i will never rewind this stream.  please
> deliver the data on a best-effort basis.  i don't require
> acknowledgement of the last byte." i.e., exactly the conditions needed
> by most real-world uses of pa_play.
> 
>  > The 2s delay is likely related to the amount of audio that is buffered
>  > by default.
> 
> i've modified the pacat-simple.c example to let me play with the
> pa_buffer_attr passed to pa_simple_new, but can't seem to find a
> combination that avoids the 2s wait.

I did some experiment to set the tsched buffer size down a little bit
and for me the wait time becomes smaller. This makes sense since the
total buffer becomes smaller and the time to wait it to be drained is
smaller.

As this parameter is not exported via module-udev-detect, so you have to
use this hack method instead:

pacmd
>> list-modules
[find the module index of your alsa card]
>> unload-module <the-above-index-you-find>
>> load-module module-alsa-card device_id="0" name="pci-0000_00_1b.0"
card_name="alsa_card.pci-0000_00_1b.0" namereg_fail=false tsched=yes
ignore_dB=no sync_volume=yes
card_properties="module-udev-detect.discovered=1"
tsched_buffer_size=<some-number>

[note the parameter here may differ from yours, but you can get it from
list-modules above, see the arguments part]

Change the tsched_buffer_size to some number smaller. How to decide the
number? Before you unload this module, invoke list-sinks and check this
property: device.buffering.buffer_size. You may need to try half the
number again and again to see how it fixes your problem.

The cons of this action is you gets poor power consumption, the wakeup
gets more and if it's too small, more chances of underrun. Be cautious.
It's more like a tuning thing. You can take a try.

> 
> removing the call to pa_simple_drain(), however, and (hack alert!)
> substituting usleep(100000) seems to do the trick, for me.  i do get
> a click between played files, though, so i'm not done.
> 
> paul
> 
>  > 
>  > Col
>  > 
>  > -- 
>  > 
>  > Colin Guthrie
>  > gmane(at)colin.guthr.ie
>  > http://colin.guthr.ie/
> 
> =---------------------
>  paul fox, pgf at foxharp.boston.ma.us (arlington, ma, where it's 62.4 degrees)
> _______________________________________________
> pulseaudio-discuss mailing list
> pulseaudio-discuss at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss

-- 
guanqun