Happy New Year, During a set of long-haul flights and long waits in airports, I tried to address one of the recurring concerns listed on this mailing list, namely the somewhat high CPU usage due to resampling. In most cases people will listen to music at 44.1kHz. watch movies at 48kHz, or start a voice call at 8 or 16kHz. Running the sinks/sources at a fixed default frequency isn't going to be optimal for all cases. To work-around this limitation, I introduced a new callback for sinks and sources which can be called to reconfigure the sampling rate. It works fine on my laptop. However there are a number of limitations on which I'd like to have comments before moving forward: - first the change is only possible when the sinks/sources are suspended. I made this conscious decision to avoid glitches. PulseAudio runs as a daemon, in most cases the sinks/sources are suspended when the user want to hear something. - I decided to have a per-sink/source implementation, and to make the feature optional. In the case of Bluetooth or other network protocols, tearing down the link and reconfiguring it may be too long. This reconfiguration is nearly immediate for a regular ALSA sink - To avoid quality issues, I limited the sinks to two frequencies, 44.1 or 48kHz. If we allowed for lower sampling rates, it'd be a problem if additional sink-inputs/source-outputs are created at a later stage with a higher sampling rate. This means that for a phone call or voice memo you would still see a resampling, but it should be lighter with integer instead of fractional ratios. - Some work would be needed to prevent system alerts from reconfiguring the sampling rate, but this is a different policy-related problem. - the sinks/sources only get suspended after a 5s timeout. This seems too high for sinks/sources that can be reconfigured quickly. It may make sense to have different values for the timeout, and make them dependent on the configuration latency.
Please review the code, give it a try and let me know if you think this is a useful feature to add. Thanks, -Pierre
0001-core-add-support-for-alternate-sample-rate.patch
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0002-core-dynamic-change-of-sampling-rate.patch
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