strange time code behaviour

rs170a wrote on 1/11/2008, 12:49 PM

I'm wondering if nayone else has experiencd this problem.

I finally started capturing several tapes from a music video that was shot last fall by some students at the college I work for.
For the shooting, the song was laid off to a DVCAM deck to get a time code reference that could be used for the shoot..
The timecode out of this deck was fed to a JVC camera with external timecode lock capability.
Everything worked fine for the shoot.
Today, as I'm playing the master tapes back, I can see the timecode on the master tape change every time a new scene was shot.
There were times that the JVC was rolled before the DVCAM but, as soon as the deck was rolled, the JVC's timecode would lock up instantly.
A problem shows up during capture though.
If the JVC was rolled first, Vegas shows the timecode on the tape start (tape time or free-run mode) and DOES NOT lock to the correct timecode after the JVC does.

If there's no known fix for this (and I doubt that there is), I'll have to go back to each clip where this happened and manually re-capture it starting AFTER the timecode on the JVC locks up.
If not, the students would have to start figuring out timecode offsets each time and they're not ready for that, especially when we're picking shots from the middle of the song.

Mike

Comments

farss wrote on 1/11/2008, 1:23 PM

I think you stuffed this up during the shoot.
You told the camera to go into record using external TC and there wasn't any. Big mistake. You've got a scene with broken TC, not good.

You could try capturing with scene detection on. The break in the TC should trigger the scene detection and cause VidCap to pickup the TC from when the VCR started feeding the camera TC.

Almost all NLEs don't like broken TC, Vegas does very well, others just don't even try. Having a tape with TC that goes backward and forwards totally screws an EDL, think about it. :)

For what you were doing, you seem to have gone to a lot of unneeded complexity. Recording the audio from the DVCAM player into one channel of the camera was all you needed to do. A pip track would have been handy too I think.

Bob.

farss wrote on 1/11/2008, 1:53 PM

Just to further explain why what you were trying to do was flawed.

When you hit record on the camera it's got no external TC so uses internal TC. Then it gets external TC. It's quite possible that the internal TC is almost at the same time as what will seconds later come in externally.
So in the one scene you can have TC that goes 10;00-15:00-09;00-56;12.

You see the problems! Firstly you've got two places in the one scene with the same TC and/or you'll have an out point with TC before the in point. This will totally confound anything.
From what I know Vidcap grabs the first frame of a clips TC and creates new TC from that by counting frames. This is good, TC can be flaky coming off a tape but Vidcap doesn't loose the plot working the way it does. Regardless as you can see from what I said previously even if it read the real TC on the tape you're still in trouble with any NLE.
If you're running cameras using external TC it really should come off a master TC generator. You want to lock audio devices to it as well, then they need to get their word clocks off the exact same master clock and that clock must keep running with almost atomic precision or you'll have all manner of problems including glitches in the audio. There's a lot of gear around that touts external TC, what you need to dig deep to fully appreciate is the cost and complexity of really using that.

Bob.

rs170a wrote on 1/13/2008, 6:13 AM

Bob, I had a funny feeling you'd be the one who would reply to this :-)

From what I know Vidcap grabs the first frame of a clips TC and creates new TC from that by counting frames.

That's what I deduced from what I was seeing on the Vegas timeline but it's nice to have it confirmed.

I think you stuffed this up during the shoot.

Not me, the students. This was their project so, with a lot of guidelines (including a warning to make sure they rolled the DVCAM deck BEFORE they rolled camera), they were pretty much left on their own.
BTW, "stuffed this up" is a much more polite way of saying "fu**ed it up" :-)
I'll have to remember that for future use.

For what you were doing, you seem to have gone to a lot of unneeded complexity.

In conjunction with another instructor, we decided to go this route as both of us have done this in the past numerous times on similar projects without this particular problem.

There's a lot of gear around that touts external TC, what you need to dig deep to fully appreciate is the cost and complexity of really using that.

This was never an issue with broadcast gear like 1" machines and a CMX controller :-)
Both the other instructor and I have designed and wired 3-camera studios so we're well aware of the various issues with time code.

When you hit record on the camera it's got no external TC so uses internal TC. Then it gets external TC.

Had they rolled the DVCAM deck first (as they were told to do!!), I wouldn't have been asking these questions.

Thanks once again for your comments and suggestions.

Mike