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Video Syncing Help please....

JohnWPB

Active Member
Ok, trying to help a friend out here that is doing a display for a local film festival.

He is recording 2 different people with 2 didgital video camera's that have timecoding in the video stream. What he needs to do is to sync the 2 video's on to seperate monitors and have them perfectly in sync when they are played back.

This will be a conversation taking palce between the 2 people so the timing is critical. as both audio's will have to be in sync.

There are definate budget restraints, so what is the easiest way to acomplish something like this?


Record both people streams to one tape, and then split it back out somehow?
Someway to sysnc the playback devices precisely using the timecoding?
Copy the video's to a computer and then sync them during playback precisely somehow?

Any suggestions are greatly appreceiated!
 

rocco

Active Member
Boy, is this ever reminiscent. I used to do this for a living in the early 90s. Things have changed since then, however.

Having time-code in the camera won't help if the time-code runs asynchronous; One camera has to be slaved to the other. Optionally, you can also use gen-lock (which a time-code camera will typically also have) to phase-synchronize the two cameras. But gen-lock will not sync a particular frame from one camera to a particular frame of the other; Time code will do this. The key is to have both cameras running synchronized, recording the time code from the same source (one of the two cameras).

Time code synchronizing is a standard feature on 3/4" tape decks. A 3/4" deck has three audio channels, the extra one is used for time code. You would simply set one deck as the time-code source, and the other as a slave, and the decks will run synchronized. 3/4" decks are pretty cheap to rent these days. If the cameras also record on 3/4" tape, you are all set.

You did not mention what media the cameras use, but if you need to get a pair of 3/4" decks for playback, it would be simplest to record directly to them. That way, the cameras don't need time-code, just gen-lock.
You can rent multi-stream DVR systems (typically 4 streams), but I am only familiar with the system from Panavision. They are more expensive to rent.

The DigiBeta system uses a similar time-code system. You could do everything a 3/4" deck could do with DigiBeta decks, but at a higher price. Some of the Super8 decks MAY do this, as well.

I've also used a few of the old Perception DVR systems (from Digital Processing Systems, Inc.), but the the ones I used required a separate PC per stream. But they were easy to sync together. They have since been acquired by Leitch Technology Corporation, and their older systems are available cheap (I got one at auction for $70).

I'm sure there are plenty of other options, and I will post if I think of them.
 

JohnWPB

Active Member
Thanks Rocco, that helps a little bit. My main concern is how to sync the playback for the presentation. The camera's being use have not been decided on as of yet, as it is pending on what is needed to sync the playback.

I was talking about recoring time code ect, just so, in the end, when all the taping has been done, there is a basis to sync the playback of both tapes.

Right now the main concern is what is needed to record the video. I remember my old Sony camcorder and VCR has a S-Linc cable to talk to each other, could somethng like this be used to sync the playback of the 2 tapes?

I thought a gen-loc device was for superimposing graphics onto a live/recorded stream? I used to have a gen-loc device on my Commodore Amiga that I used to use for titling and graphic overlays onto video.

So to sum it up, the first concern is how to record the video, so it later can have a basis to be synced with each other.

Second, a way to play the 2 seperate streams, synced, to an audiance. Weather it be using a a computer, 2 computers, the camera's themselves, or something that hasn't been thought of yet :D
 

rocco

Active Member
I guess my post was a little rambling. I covered all of those questions, but not in a comprehendable way. :D

First: Gen-Lock.
A device that has Gen-lock simply means that it can output a video signal that is synchronized with an incoming video signal. By synchronized, I mean that the horizontal and vertical sync pulses occur at the exact same time for both video streams. It is a pre-requisite to overlaying video: If two video signals are not phase-synchronized to each other, you cannot combine them (and get any useful results).

If your cameras are gen-locked, they will at least be recording at identical frame rates. This is a must in order for them to stay synchronized on playback. But that will not help to get the two playback tapes lined up before playback. A 'clapper' or 'bloop light' are often used to do this, but it is more awkward to setup than time-code. Time-code can both synchronize the cameras and synchronize the playback decks, as well as keep the two play-back tapes lined up. However, there are a lot of quirks to worry about with time-code.

So to answer your question on how to record the video, the important thing is that the cameras are able to be slaved. Either to time-code or gen-lock. If you are not shooting on location, I would play it safe and record on the same decks that will be used for playback. This way, only the deck need to support time-code, and you can record the time-code on the two decks simultaneously. The cameras only need to gen-lock, or slave to time-code.

Another question. Does the playback occur once? Or does it have to repeat automatically? Repeating automatically would certainly complicate things.
 

JohnWPB

Active Member
beleive me, I thought of the old "on 4" addage. I have a feeling it would look like a 1960 Japenese Godzilla movie though with the voices :D
 

rocco

Active Member
Squintz said:
I recomend two very accurate finger to conserve money.
I have to admit that that may be the simplest solution. Two decks probably won't get far off over time. You could sync the tapes initially with a Bloop-light.
 

rocco

Active Member
OK - New idea.

DVDs have the ability to loop, pause, have menus and other features I have no idea about. If you can get a DVD authoring software package, you could create a loop on two DVDs with the exact same number of frames. You can make a common bloop frame the start point for both loops. You could then use two identical DVD players, and start them together with one remote. After a while, if they drift out-of-sync, you could resync them with the 'menu' key on the remote.

You would still need to record with synchronized cameras, but that part is easy.
 
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