On Mon, Jun 20, 2016 at 01:08:27PM +0200, Pierre-Louis Bossart wrote:
The ALSA API provides support for 'audio' timestamps (playback/capture rate defined by audio subsystem) and 'system' timestamps (typically linked to TSC/ART) with one option to take synchronized timestamps should the hardware support them.
Thanks for the info. I just skimmed Documentation/sound/alsa/timestamping.txt.
That is fairly new, only since v4.1. Are then any apps in the wild that I can look at? AFAICT, OpenAVB, gstreamer, etc, don't use the new API.
The intent was that the 'audio' timestamps are translated to a shared time reference managed in userspace by gPTP, which in turn would define if (adaptive) audio sample rate conversion is needed. There is no support at the moment for a 'play_at' function in ALSA, only means to control a feedback loop.
Documentation/sound/alsa/timestamping.txt says:
If supported in hardware, the absolute link time could also be used to define a precise start time (patches WIP)
Two questions:
1. Where are the patches? (If some are coming, I would appreciate being on CC!)
2. Can you mention specific HW that would support this?
Thanks, Richard