> > > > > > Before applying this, I'm curious, do you have a use case for realtime > > > time stamps ? > > > > Yes. ffmpeg uses wall clock time to create timestamps for audio packets from > > ALSA device. > > OK. I suppose I shouldn't drop support for the realtime clock like I wanted to > then :-) > > > There is a bug in ffmpeg describing problems to synchronize audio and > > the video from a v4l2 webcam. > > > > https://trac.ffmpeg.org/ticket/692 > > > > To workaround this issue, ffmpeg devs added a switch to convert back > > monotonic to realtime. From ffmpeg/libavdevice/v4l2.c: > > > > -ts <int> .D.... set type of timestamps for > > grabbed frames (from 0 to 2) (default 0) > > default .D.... use timestamps from the kernel > > abs .D.... use absolute timestamps (wall > > clock) > > mono2abs .D.... force conversion from monotonic > > to absolute timestamps > > > > If the v4l2 driver is able to send realtime ts, it is easier synchronize > > in userspace if all inputs use the same clock. > > That might be a stupid question, but shouldn't ALSA use the monotonic clock > instead ? > This isn't stupid. I had the same though after replying you. Intuitively, I would think that monotonic clock is a better choice for multimedia. I am just speculating but I would say that ffmpeg decided to use realtime clock as the standard clock throughout the project for portability purposes since it is a cross-platform project. Now you know how I ended up trying the clock=realtime option. IMHO, if the option is there, it should be working but just removing it could also be a valid option. I feel that this could bring some new problems if it stays there because, I'll be honest and say that I didn't test the driver behavior when the time goes backward.... -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
