Hi,
The UAC2 ch. "5.2.4.8 Latency Control" specifies latencies optionally reported by the device for individual entities. Especially the overall terminal latency TE_LATENCY_CONTROL is interesting.
Some video players include the delay reported by snd_pcm_status_get_delay into their AV sync calculation.
A linux USB audio gadget can perform some advanced DSP, which including the output device latency can result in a non-negligible overall latency. The gadget userspace software could configure the actual value to be reported by the gadget to the host in the selector UAC2_TE_LATENCY (audio_v2.h). The UAC2-specced max value of over 4 secs is more than sufficient for standard use cases.
But I could not find any read of the UAC2_TE_LATENCY control selector in the snd-usb-audio driver ( https://elixir.bootlin.com/linux/latest/C/ident/UAC2_TE_LATENCY ). Please does the driver include this value into the overall delay reported through alsa-lib? If not, would it make sense to add such support?
Thanks a lot,
Pavel.