Film/video sync

[Mick]

I had an interesting time the other day. We were shooting a live 24frame HD video in the background, projected onto a giant screen in a lecture hall setting. The lecturer was in the foreground and the screen was his whole background. There was dialogue from the lecturer which was reacted to and answered by the full face on the video. The film camera pulled focus back and forth from the lecturer to the video screen. Setting up the playback so that the video audio came into the hall and the audio from the hall was sent to the actor on the live feed was quite the conundrum, but kudos to Cooper whose mixer's routing versatility saved the day.

The problem that arose was this. There is an inherent delay between the live audio and the projected video. The audio arrived in the auditorium instantly but the video was off by about 3/4 frames, a noticable delay. The film camera audio was in sync but the video was not. As all this was in the same shot there was no room for fudging the video audio as that would have affected the film audio sync. Anyone confused yet?

I was wondering what any of our post production posters would do in these circumstances if the editor decided to remain on this shot for any appreciable amount of time, making the sync issue rather obvious. I'm sure that the final cut will be busy enough to render the problem a non-issue, but what if?

Regards

Mick

[rich]

hi Mick. would delaying the playback audio before it reaches any comms/PA so that it was in sync with the projected video not get around this? i remember that bheringer make a little box with programmable delay and is cheap but doesnt look that sturdy. i've also seen an arri unit with a handy table on it that tells you you delay per frame in ms for any given framerate which is also pretty rugged and has xlrs if i remember correctly.

[Mick]

That would work if you know all this before shooting. I'm just curious about what, if anything, can be done to correct the situation in post once the film and audio have been synced.

[curleysound]

While Cooper is absolutely a superior quality mixer, the Yamaha 01V96 has digital delay available on any channel, and very flexible routing. With the 01V96, this problem would have been solved by a few extra button pushes. You could have one as a "Just in Case" mixer for (at worst) 1/5 of the cost of a Cooper.

As far as post goes, if the track that is delayed is on an iso track, couldn't they bump it up in the timeline accordingly?

[BVS]

Even if it wasn't iso'd it could be split out in post,as 3/4 frames won't make any difference unless the live stuff is actually over the screen stuff.Then it could be tricky and they would have to cross fade between the pulled audio and the onscreen.Quite do-able tho.

[Mick]

That's the problem. Everything is live, the film and the video, recording simultaneously and locked together.

[BVS]

Yes I understand Mick.But you talk about post production.Is it a totally live to air show or does it have a post production?

I did a show recently with the same problem but it was fixed in post.

I also had a live feed from the inhouse console on one track and my schoeps live on the other.The difference in time between the two,I measured at 22msecs and they pulled it up in post and mixed it with the onstage stuff from the feed.It actually sounded very good,surprisingly.

[Sergio Sanmiguel]

Using a microwave remote feed you should be able to adjust for delay between video & audio at the SAT truck. That's how all Live news broadcasts are done every day. Now, if you're talking fiber, then there shouldn't be any delay on the stream at all... Anyhow, if they're also shooting film they must be able to compensate for that in Telecine.

[BVS]

In fact if I was doing this post,I'd pull up the delayed track and lay it down then using the front person's  track as is with the correct sync and cross fade between them as the focus pulls.As long as there's the smallest space between words or breaths it'll work.