On 22.03.2016 12:51, Tanu Kaskinen wrote:
On Tue, 2016-03-22 at 12:33 +0100, Georg Chini wrote:
On 22.03.2016 12:20, Tanu Kaskinen wrote:
On Tue, 2016-03-22 at 10:11 +0100, Georg Chini wrote:
Hi,
when a sink is started, there is some delay before the first sample is
really played.
This delay is a constant part of the sink latency that will be always
present, so the
minimum sink latency cannot go below that start delay.
Would it be acceptable to adjust the latency range for the device after
each unsuspend
to reflect that?
USB devices (those I have access to) for example have a startup delay in
the range of
10ms, but have a latency range that starts at 0.5ms which does not make
a lot of sense
in my opinion.
I don't understand why the startup delay would limit the minimum
latency once the stream is flowing. Imagine a sound card that is
powered by a nuclear power plant. I don't know how long it takes to
start a nuclear power plant, but let's say it takes a couple of days.
Now the sound card startup delay is a couple of days, but there's no
reason that the audio latency has to be a couple of days once the power
plant is running. Where would all that audio be buffered anyway?
Hi Tanu,
you are wrong.
I don't believe you :)
Look at the code of alsa-sink. It never drops samples. The only way to
compensate
for the startup delay would be to drop audio as long as the sink is not
yet playing,
but that is not done. I could try to implement that however and then you
would be
right, but with the current code at least for the alsa-sink the startup
delay will persist.
I expected a reply like this. The sink is started up at
the moment
when you write the first data to the buffer, so all following data can
only be played
when the previous data has been handled. This means, that the startup
delay will
persist forever unless you are dropping samples (which you would have to
do in
your example above but which is not done in pulseaudio).
Actually you can see that startup delay when you use an oscilloscope because
the real latency is off by that amount.
What is the "real latency" you are talking here? Is it the full end-to-
end loopback latency or the sink latency? The loopback latency is
(somewhat) constant, but the sink latency varies all the time, because
sometimes the sink buffer is full and sometimes it's empty.
--
Tanu
It's end-to-end latency of module-loopback.
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