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Topic: Getting A/V sync right...
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 09-04-2019 07:00 AM
There's no way to set A/V sync per film/CPL on any server I know. Doremis allow to set a per-CPL audio mapping, but audio delay is not part of that.
Some audio processors allow to specify a delay per preset (e.g. AP20/25). As the Datasat offers loads of free presets, it shouldn't be a problem to make a few copies of existing presets and adjust global delay in them, to be addressed from within SPLs.
I think a CP750 can only adjust global delay per input. However, it may be possible to adjust global delay during runtime using automation commands (cp750.sys.dig_X_global_delay - 'X' for input number). So you could put a suitable delay value into an SPL associated with that CPL. Don't know if that value is applied right away, you would need to test it. The max value of 250ms should be easily discernible during a test.
While it's easy to find proper sync with a test-clip, I'd find it rather complicated to do that with varying live footage (unless the sync is severely off - which I would consider not a sync issue, but a broken DCP). If you take the time sitting in the auditorium and using some remote control option for your processor, it may work out well enough.
- Carsten
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 09-04-2019 11:01 AM
I'd say what you say is true for the average professionally created DCP...
But in reality, it depends on what material you're working with. Professionally made DCPs seldomly have any A/V sync issues, but the DCP format is somewhat of an oddball format for indie producers. They often don't even have the proper tools to test their DCPs themselves, so they just export it or look up some on-line tutorial and are done with it. I actually prefer them to deliver some kind of MP4, MKV or other common format, instead of a DCP with issues.
But as a result, I've seen some crappy productions over the years and some have their audio so much out of sync, it becomes a challenge to get right and yes, I've had one DCP once that had the audio so much off-set to the "negative side" (as in too early), the only way to compensate it was on the server. Sure, that DCP was clearly defective, but sometimes you need to work with the stuff you're handed...
Like Carsten mentioned, getting A/V sync right on "live content" isn't always easy and can be quite a frustrating thing to do. I also tend to look for short sound effects with a high impulse like gunshots, doors closing, etc., as they're far easier to track and time than someones mouth movements.
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