On Sun, 2011-03-06 at 16:30 -0600, Pierre-Louis Bossart wrote: > This is the second version of my endeavors to remove or make SRC > simpler when possible. An idle non-network, local or passthrough > devices will be suspended immediately when there aren't any > inputs. When a new input is connected, we try to resume with the best match > between requested sample rate and sink sample rate. To make things > simple, the sink can only support a default and an alternate rate, > typically 44.1 and 48kHz. Of course the feature is disabled when both > rates are identical (if the sink cannot be reconfigured). Tests with > HDAudio and USB show a negligible added delay but a nice reduction of > CPU activity. An alternative idea: At sink-input trigger a reconfiguration if possible/supported. Sinks expose a reconfigure_rate method (I'm sure we can find a better name) if they can do a quick switch. In the ALSA sink, this function would check if there are no sink-inputs attached and the rate is supported, and then send a message to the I/O thread to do the actual reconfiguration. We would cache the rate if suspended and apply on unsuspend, or do a suspend-reconfigure-unsuspend if it's running. With this, we can replace default-sample-rate with a minimum-sample-rate (anything below this gets upsampled), and use the sink-input sample rate if supported (or an integer multiple as your code does). The advantage of course is that we're no longer restricted to two sample rates. I did a quick walk over the code and this seems feasible. I'm doing something similar (but far simpler) for passthrough mode in alsa-sink - when a passthrough input is added, I do the suspend-update_rate-unsuspend if required and it seems to work fine. Does this make sense or am I missing something basic here? Cheers, Arun
