[pulseaudio-discuss] Detecting low buffer level of a sink output

Marcel Müller mm0pointer at maazl.de
Sat Apr 14 09:35:39 PDT 2012

I tried to detect the buffer level of a sink output by calculating the 
difference between write_index and read_index in pa_timing_info. But I 
did not get the wanted effect.

In fact the difference never falls below the exact equivalent of 2000ms. 
Even if the sound has completely stopped because of a buffer underrun. 
Furthermore, the lowest level of exactly 2000ms is not reached before 
the sound stops, but somewhat later. I am curious whats happening here. 
Is there a better criterion than the buffer level?
I considered the over all latency, but it depends on user configuration 
of the PulseAudio server.

I use the asynchronous API and the main loop runs at time critical 
priority. But I do not want the entire engine to run at time critical 
priority all the time, because on slow machines with complex filters the 
thread may eat 100% CPU, which causes the UI to lock up. To avoid this I 
want to raise the priority of the engine only if the output buffer is 
low and only for a limited period. So if a user uses a configuration 
that is too hard for his CPU, he gets drop outs instead of a dead lock.


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