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View Full Version : Stretching video for multi-cam track in Vegas


redpill
2009-06-20, 10:02 AM
I have a 2-cam show I'm working on in Vegas Pro 8.0. I thought I was done with it, had it rendered and authored, but when I watched it on the big screen I noticed that one video source is off by about 5 frames by the end of the 85 minute set. It seems to be OK in the beginning and get worse toward the end of the set. I had saved the project at various points along the way so now I'm trying to back to the point before the multi-cam track is created and stretch the out-of sync video source. After I do that, I create the multi-cam track, but the one source is still out-of-sync by the same amount no matter how much I stretch it. What am I missing? It's killing me!

I also noticed that each song in the audio track is separated by about half a frame. I think this is why I ended up with the discrepancy since 10 gaps times half a frame equals 5 frames. But if I close the gaps to shift the audio it will make the other video source out-of-sync. I want to be able to stretch one of the video sources.

xjsb125
2009-06-20, 07:21 PM
You may have some dropped frames in there. I was trying to sync another miniDV source last week and couldn't get it to line up properly. I went back, song by song and found several 2 second instances where the video skipped frames.

ChrisF
2009-06-29, 07:01 AM
always pay attention because it says after transferring if any frames where dropped. i check it every 10 mins of transfer if possible and if frames drop i restart the tape from the beginning

for synching multicamera i find a spot right in the middle of the clip to make a sync point with the audio peaks. it will be slightly off in the beginning and and slightly off in the end but in the middle it will be perfect. it will give u most accuracy all the way thru the tape and its better than doing a time stretch because that reenders frames. ive never needed to stretch video to get it to sync. only for when syncing 2 audio sources.

Silver Stallion DVDs
2009-07-04, 11:33 PM
Even modern day video cams do not operate at exactly the same speed...just the nature of the beast.

But this is a very simple problem to fix.

For starters - you don't stretch (or crunch) video. Just doesn't work. Audio is a different story - but that's another thread for another day.

You're usually only showing one angle at a time, i.e., you are alternating between videos. During a stretch when you're showing the 'longer' of the two angles, split the 'shorter' angle and bump the portion to the right of the split to the right one frame. If you're off by five frames, you'll need to that four times. Space out the splits evenly across the length of the video.

If the problem resulted from dropped frames (which doesn't appear to be the case), then you'd handle it differently. But if it's just a matter of the two videos drifting out of synch - do what I said above and you'll be all set.

To check the synch in Vegas, just pull down the opacity line on the video in the top line of the time line to about 50%. You'll then be able to watch both videos at the same time. Watch the drum sticks or the singer raising an arm or whatever. Just make sure they are in perfect synch and you'll be where you want to be.

saltman
2009-07-06, 11:07 AM
Set your capture to stop on dropped frames. They suck. Yes a few is that not that big of a deal but you should not have any if everything is setup properly.

SS gives good advice about dealing with a sync problem. Never stretch the video. Multicam is very easy to deal with this problem. The cuts give you the opportunity to slide the one not on screen over to get back in sync.

Vaast double take screws up the sync sometimes. I don't use it anymore. Maybe that is your problem. Use the mutlicam in Vegas 8. It can preview all your video at the same time. It also has better tools than Vaast DT.


Before you make your multitrack n Vegas8 make a copy of your video and audio. You can use this to shift and splice if something gets off also. That will save you a lot of time.

stantheman1976
2009-07-06, 11:41 PM
The only time I've ever had problems with sync was when I had dropped frames. I've done stuff that was 80-90 minute segments and it was only off by 1 frame at the end. If you've got a noticeable difference dropped frames are likely your problem.