On Fri, Oct 18, 2013 at 10:36:17PM +0100, James Stone wrote: You can import the video in Ardour3, this will give you a video timeline in Ardour's editor (i.e. a 'track' consisting of images) as well as synced video playback in a separate window. Within A3 you can do with the audio whatever you want, and when done you can export the whole to a new video file. I used this a few weeks ago to edit and mix the audio for a 1.5 hour documentary, and it worked rather well. You may need some iterations when setting things up (getting to know the quirks of the import and export dialogs) but otherwise it works well. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow)

On Fri, 2013-10-18 at 22:36 +0100, James Stone wrote: I don't know research about it, but there are recommendations for video and film. "The accuracy of A/V synchronisation at each stage should lie within the range of Audio 5 ms early (soundbefore picture) to 15 ms late (sound after picture). Limits of the relative timing of the sound component of a television programme relative to the corresponding picture component Sound before picture Sound after picture ≤ 40 ms ≤ 60 ms" - http://tech.ebu.ch/docs/r/r037.pdf "For television applications, audio should lead video by no more than 15 milliseconds and audio should lag video by no more than 45 milliseconds.For film, acceptable lip sync is considered to be no more than 22 milliseconds in either direction." - https://en.wikipedia.org/wiki/Audio_to_video_synchronization#Recommendations http://en.wikipedia.org/wiki/Lip_flap#Recommendations Related: http://en.wikipedia.org/wiki/Clapperboard

On Fri, Oct 18, 2013 at 11:25 PM, Monty Montgomery <xiphmont(a)gmail.com> wrote: OK - that's encouraging at least! I meant in terms of timing shift of audio vs video? James

On Fri, 18 Oct 2013, James Stone wrote: The same player might have non-sync video/audio depending on the audio output path. One would expect the player to compensate for the delays cause by decoding, but then the audio may go straight to the alsa device or through pulse which adds latency or through jack (where you can set the latency so one time might have a different delay than another) or through gs first then through who knows what. Some of the sound servers may have variable latency depending on cpu load too. That is not even touching the video chain (outside of my knowledge), but you get the idea. On any reasonably fast computer one can set up an audio/video chain that will work in sync, but change any one part of that chain and sync may be no more. So if you are looking from a distribution POV, you have no control of what the audience will play your video on. If you are using it in an institution, then all the machines may be the same as well as the OS/SW and so there is a better chance. Keeping the decoding work as low as possible and using sample rates and frame rates that match the sound serve/audio IF and work as close to the GPU setup as possible reduces things like resampling/resizing and reduces cpu load and brings different speed HW closer to matching. For example, if your audio is using opus as an codec, then 48k sample rate in the sound server/audio IF will result in no resample to match the codec ouput. But if the audio card is set to 44.1k then the audio must be resampled. However, many of the videos available on the Inet have audio at 44.1k and so running the audio IF at 48k would mean a resample step for them. So it would seem it would be impossible to make sure that audio and video are always in sync on every machine. The recording and encoding sw can shift the audio with respect to the video. Then check it out on the machine/OS that most of your target audience uses. I don't know how the windows audio server works, however, the intel HDA audio interface assumes 48k (or 96k or 192k... though even at these speeds it seems the bus runs at 48k with just more parallel data). So I would guess the default windows setup would be 48k. I don't really know though. -- Len Ovens www.ovenwerks.net

On Sat, 2013-10-19 at 00:58 +0200, Ralf Mardorf wrote: Even latencies by the hardware and software are always equal in this ideal world, for all players.

On Sat, 19 Oct 2013, Ralf Mardorf wrote: Yes of course. The brain is used to dealing with audio lag at varying distances. I was playing around with VLC which has a sync control. It seems I could set it to be off a bit but my brain seems to correct it with in some seconds... Or maybe every time I change the sync the audio and video restart from a known point of sync and then drift... As you said before, the brain notices leading sound much sooner than lagging sound. That would be the way it is in nature. The drive-in theaters I have seen have in-car sound (often using the car's radio), so the delay is minimal. I wonder if indoor theater operators set the audio ahead just a bit so it hits the second or third row in sync. It would probably mess with the surround sound too much. I will say I have not noticed sync problems in the theater even though we always sit at the back as my son doesn't see well above horizontal. -- Len Ovens www.ovenwerks.net

On 19/10/13 07:23, Len Ovens wrote: a neat thing (mentioned before on this list I think) ... try shifting your gaze to an analogue clock with a second hand that jumps every second and as you do so compare the perceived time before the first tick with the time between the other ticks. Generally the time to the first move seems longer than the others. An explanation for this is that our brains maintain a certain latency between receiving sensations and building a model of the world from the combination of these (presumably for the same reason a computer does, to give time for all the sensations to be received and processed) and that when we shift gaze quickly the model we build is extrapolated back through this latency, including assuming the stationary second hand was stationary through this whole buffering time. I guess it is related to our reaction time, and also related to the importance of the parts of the nervous system that process and respond directly, not going back to the brain at all. On a more speculative level ... I've always noticed that if I burn my hand on a soldering iron I smell the burn before I feel the pain, and I think I actually pull my hand away before being aware of either. Maybe smell is not synced in the same way as vision, touch and sound are?? As far as video and audio sync go ... with a live actor on stage, and a camera on their face with a big screen behind them, in a space where the actor is speaking and maybe 3 metres from the front row, I found that a video system without genlock but using several PCI analogue camera inputs mixed together with openGL gave me between 1/2 and 1 1/2 frames delay, the video lagging behind the live voice and that was just acceptable in context, but quite noticeable, while most other video input systems where impossible (especially firewire!). Simon