Howdy, Since this was missing in PulseAudio, I created a loopback module where input sound can be redirected to a sink. That removes the need for the silly parec|pacat workaround. Basically the module creates both a sink_input and source_output. When there's data available from the source, a push callback is called by the IO thead. Likewise when the sink has eaten the data a pop callback is invoked. Since both callbacks are called from two different threads, I pushed incoming data into a memblockq and read from there in the pop callback. I figured it this would enable zero-copy operations. Works fine with a USB mic and PC internal speakers, and vice-versa. With a low-enough latency you can use it for karaoke apps, but that was not the initial goal... Since this was the first time I really looked into PulseAudio internals, I have a number of questions: 0. is there a better way to do this loopback? I did not find any module that relied on the push callback, and I only saw the pop callback in very limited number of modules. 1. latency: I configured both sink and source to the same latency, yet in the push callback I see the number of samples can vary. If I program the source with a 10ms latency, I would expect to get a 10ms buffer. Is this due to some kind of scheduling thingy? Likewise when I configure the source to have a 20ms latency, I get a buffer of ~10ms. Is this normal? 2. I assumed that the memblockq routines (push, peek and drop) are thread-safe, is this a valid assumption? 3. For now the source and sink are synchronous but if they are not, how can I enable a sample-rate converter to correct for clock drifts? I see some code for SRC in both the input and output IO threads, however I don't understand how the tracking would be done. 4. someone described a use case with BT, I would need to load the same module twice, i.e. load-module module-loopback source=bt-src sink=speakers load-module module-loopback source=mic sink=bt-sink Is there anything specific I need to do for this? 5. I started from the module-sine code, however I have no idea what to do about some callbacks, specifically rewind and state-changed. Does anyone have a description of what's expected here? I am working through red tape to release this code. Will probably take me more time than writing the code... Thanks for your feedback. Cheers - Pierre
