How important is Genlock for...

Tech Diver wrote on 8/31/2006, 12:12 PM
I shoot a fair amount of performances of small music bands to create shorts videos as part of their promotional material. I use two (or sometimes three) cameras to do this where one of the cameras is stationary and records the entire performance to capture both a full stage view and the soundtrack (which is usually fed from a mixing board). The other camera(s) move about and capture several seconds of footage at a time from various vantage points.

During editing, I lay down the footage from the stationary/continuous camera as my "master video and audio tracks" and overlay the clips from the other cameras, synchronizing the placement of the overlay clips MANUALLY by looking at visual cues of sound peaks lining up with the "master audio track". Once aligned, I remove the overlay audio and just use the "master".

My question is: would Genlock-enabled cameras make my task easier/better. Note that I am planning to buy a Cannon XL-H1 next March, and another a few months later.

Comments

Logan5 wrote on 8/31/2006, 12:28 PM
Do you mean “slaved” cameras or jam sync the timecode for your shoot?

Genlock- is use to sync the video signal for cameras for such things as live switching among other things.
rs170a wrote on 8/31/2006, 12:53 PM
The other camera(s) move about and capture several seconds of footage at a time from various vantage points.

When you say this, do you mean that the other camera(s) start/stop constantly? If yes, this makes editing a nightmare. Much easier (especially in the edit suite afterwards) to roll all cameras continuously. Tape is cheap.

Mike
ForumAdmin wrote on 8/31/2006, 1:08 PM
Genlock is not needed if you are capturing later (from tapes recorded in separate cameras).
Tech Diver wrote on 8/31/2006, 1:29 PM
Logan5: I do not plan on any live switching. I understand how Genlock would be essential for that.

Mike: Yes I do start/stop the mobile cameras often and it does make the editing very time consuming because I have to align every single clip manually. If I do a continuous roll as you suggest, is there a possibility of drift. That is, if I compare the footage of two different cameras after 30 minutes of continuous/uninterrupted shooting, will the captured events be synchronized within 1 frame of tolerance?

Admin: are you suggesting that I keep using my current methodology?
Former user wrote on 8/31/2006, 1:32 PM
Unless the cameras are tethered with a genlock/timecode synchronizer, there will always be some drift. How much depends upon the quality of the cameras. It would still be easier to resync if you are within a a few frames, than to have to resync everytime the camera is turned off.

Unless you need to stop the cameras, I would agree to the idea of just letting them roll.

Dave T2
Logan5 wrote on 8/31/2006, 1:55 PM
Years back when I did military test shots we used Timecode set to Free Run. <assuming your cameras have the switch.

If you have all your cameras timescodes synced up and on free run – Then even if one of your cameras stops and starts recording you will always have the same TC.

If worked well for many test shots. Also it was helpful to have a event flash in frame, but that not needed if you just need TC all synced.
farss wrote on 8/31/2006, 2:28 PM
Certainly being able to lock all the cameras clocks together is a plus. That way all the audio samples will be at the exact same frequency as will the frame rates.
You don't have to run cables between all the cameras either, you cab get a system that broadcasts TC over RF to little receivers that hook into the cameras or you can get a little external generator that you initially calibrate against a master, good for around 1 frame per week.
Be warned though, this is all broadcast gear and generally priced accordingly.

Bob.
johnmeyer wrote on 8/31/2006, 2:42 PM
I am a computer guy who didn't "grow up" in the video world. Therefore, this may be wrong. However, I think genlock was designed to get all cameras scanning at the same moment in time so the signals could be fed, in real time, through a switcher and all the scan lines would start at precisely the same time. Only in this way could they be mixed, in order to do insets, crossfades, etc.

By contrast, when dealing with video that has been digitized and which is not in real-time, this feature is not needed in any way.
farss wrote on 8/31/2006, 2:57 PM
It's needed in every way John.
Without it the clocks in the cameras run at their own frequency so over time things get out of sync.
Just try doing a 1 hour shoot with three cameras that aren't locked, I've done it, they drift, you can fix it in post but it's a pain.
And you have to do it carefully, otherwise you're reampling all your audio and video.

However the term Genlock is being used a bit freely here, it does typically refer to live switching, ensuring that all vision is in sync so it can be switched without loosing sync.
Being able to lock all the cameras clocks even when they're all running in iso is very usefull. Having audio recorders that lock is also very usefull. All pro audio gear also will lock to external references.

Bob.
Steve Mann wrote on 8/31/2006, 9:14 PM
I think that the precision of the data clocks have gotten much better in the past two years. I shoot three cameras of stage performances and have never seen as much as a single frame drift in any of the cameras over one hour. I wouldn't even imagine being anywhere near frame-accurate with older analog cameras.

Steve M.
Tech Diver wrote on 9/1/2006, 10:40 AM
Steve, when you shoot stage performances do you keep all your cameras continously rolling?

Logan5, yes my cameras do support TC free run. How do I go about establishing the initial timecode synch?
farss wrote on 9/1/2006, 6:58 PM
Get all the cameras together and use one remote. Use the remote to set initial TC, they'll all be in sync.

Bob.
vicmilt wrote on 9/1/2006, 7:22 PM
Let me sign in with a good 'ol low tech, cheapo way to sync yer cameras...
I've done this dozens of times and it's perfect.

You buy three cheapo digital clocks from Radio Shack - ones with big numbers. One clock for each camera. Set them all to the same time of day.

Anytime anyone of your camera ops starts his camera, the first thing he shoots is the "time code" off his clock. Then without stipping the camera he shoots the show until he feels like stopping - totally independent.

Line up your first "master" camera on a timeline, and offset the code to match the time of day from the first clock.

Now all you've got to do is find the correct time of day for each of the other cameras and put them in place. You'll always be within a second or so, and your scratch tracks will tell you exactly where to go to get exact sync.

Hey dude you owe me two grillion hours of syncing time.

best (with a smile),

v
farss wrote on 9/1/2006, 7:31 PM
Good idea, I think I should have mentioned that my method only works with Sony cameras recording in DVCAM.

Bob.
technobaba wrote on 9/2/2006, 3:51 AM
I edit plays with mulitple cameras. Advice: Leave all cameras going. Much easier. Drift is a very small problem with DV type cameras. Over a 1.5 hour play i have to resync (cut and slide audio) in max only 1 or 2 places. (With older Hi-8 cams it may be every 10 min.)

Example right now: 8 tracks of ProTools audio to sync with 2 tapes from each of three cameras. I needed no sliding except to match each camera's tape with the others. i.e. the lipsync was fine for almost an hour! (Different models but all cameras were Panasonic.)
farss wrote on 9/2/2006, 4:43 AM
I think using at least cameras from the same manufacturer or better still the same model helps. I know there's some significant disparity in audio clocking between Sony and Canon cameras.

One of the biggest issues I've had with multicam wasn't between the cameras (they held together quite well over 90 minutes) but between the cameras and the venues CD players.

Post the Infiniticam edit I synced the music from the CDs back into the vision and even over a 5 minute track the difference was a big issue, easy enough to fix in Vegas of course.

Bob.
Steve Mann wrote on 9/3/2006, 1:06 AM
"do you keep all your cameras continously rolling?"

We only stop them to change a tape, and then it's at a prearranged time on the program. (Usually intermission).

If the Catapult ever comes to market, I'll just let them run for the entire performance.

Steve M.