Can you get the system latency?

[tGrothmannFluffy]

Hi there,

I am trying to get the system latency. Basically, I want to know (roughly) when the samples I wrote to the output are ending up at the speaker.
I know this is probably highly os and device dependent.

I found this oboe (android) function to get this value. But I was wondering if/how I could access that.

I am working on Android and iOS.

[morajabi]

I'm interested in this for macOS. Use case is for using acoustic echo cancellation that works better with exact latency metrics.

[j-n-f]

Also interested in this.

From what I can tell the StreamInstant values in callbacks are just giving block_size / sample_rate. The value doesn't match what my driver reports (it's close, but less than the actual values).

From a quick look at ASIO and ALSA they both return this information in frame/sample counts. It would be useful to know what this looks like for the other backends.

It should be possible to use that data to provide more accurate StreamInstant values (e.g. for callback and playback values). Since ASIO/ALSA provide the value in frames/samples, it might be nice to include that at the level of stream config (without having to derive it from a bunch of floating point values in callbacks).

[j-n-f]

Here's what I was able to scrounge up.

My previous comment on putting this latency information at the stream config level may not always be possible. If Oboe can even provide this value, it sounds like it might be dynamically changing block size and even latency while a stream is still running.

If some backend can't provide more accurate latencies then the existing heuristic was the best you could do anyways.

This should be enough to start experimenting.

backend	api	format	comment
ALSA	snd_pcm_delay	frames/samples
JACK	???	???	not sure, guessing you just use ALSA to fetch this information
WASAPI	IAudioClient::GetStreamLatency	100ns increments
ASIO	ASIOGetLatencies (ASIO SDK 2.3, page 14)	samples/frames	must call after ASIOCreateBuffers Driver may notify host (cpal) of kAsioLatenciesChanged (ASIO SDK 2.3, page 9)
CoreAudio	AudioObjectGetPropertyData (for kAudioDevicePropertyLatency)	???	There's also some discussion on a mailing list on how we may need to read several properties
Oboe	???	???	Oboe is complicated, and it seems like it might dynamically adjust block size while running. Might just have to use existing heuristic for this one. (further reading)
Emscripten	???	???	Not actually sure how this backend works, can't find documentation

[marcpabst]

Not sure if this is still relevant for @tGrothmannFluffy, but I've started to implemented a latency() method for Stream that returns the latency in samples/frames. @j-n-f's research was quite helpful!