7 Replies Latest reply on Feb 8, 2010 8:39 AM by the_wine_snob

    sync multiple video tracks: same action, shot at different times

    trevorrotzien

      I am working on a video of a Tai Chi demonstration. I have 4 video tracks, all taken by the same camera at different times. My goal is to have each of the 24 forms appear to be executed at exactly the same moment across the 4 different camera angles (even though the video wasn’t shot at the same time).

      What helps: each video track is of the same expert demonstrating the same 24-step form to the same piece of music.

      What hurts: Even though he is very consistent, the exact timing in each demonstration is slightly different.

      I have an idea on how to sync the 4 video tracks, but it would be very laborious.

      Question: Is it possible in Premiere Elements (I have version 4) to set a sync point in each of the 4 video tracks, and have each track automatically time stretched so that the sync point is lined up across all tracks? (and then repeat for each of the 24 forms – positions?)

        • 1. Re: sync multiple video tracks: same action, shot at different times
          the_wine_snob Level 9

          Now, are these going to appear as PiP (Picture in Picture), in a 2x2 matrix?

           

          If so, you might want to alter the time on some to match perfectly (or very nearly so). Time Stretch can be either a +, or a - rate.

           

          Otherwise, if you are cutting, the Time Stretch might work to, should you be rapidly cutting between the 4 takes.

           

          I do not know of any auto, or semi-auto way to match things up.

           

          Good luck,

           

          Hunt

          • 2. Re: sync multiple video tracks: same action, shot at different times
            trevorrotzien Level 1

            Hunt, thanks for the quick reply.

             

            The intended PiP layout is 2 side-by-side, best two angles for each of 24 forms from the 4 tracks, with a strip at the bottom reserved for form descriptions (each Tai Chi routine has a fixed number of forms in a specific sequence).

             

            Here's the basic approach I was going to take (though I am hoping there is some time saver I haven't thought of):

             

            For each of the 4 video tracks: trim front and back off to ensure there are no excess frames in terms of the Tai Chi routine start to finish.

             

            Time Stretch each video track to the length reference audio (same song the routine was performed to, but ripped from CD rather than ambient) - This will result in the same basic content over the same time period in each track.

             

            Problem: Due to small differences in the time the performer took to go through the individual forms, the forms don't necessarily sync-up even if the total time is equal.

             

            The brute force method I could use to ensure each of the 24 forms are sync ‘ed within each track:
            Cut each video track into 24 segments, with each cut at a specific point in the performers motion (this will be 23 x 4 = 92 cuts – very time consuming. Then I would time-stretch each of the 4 angles for each form so that the start and end of each cut would match (not just the total time), so that at playback, each form would appear to be performed at exactly the same time, so that fades or cuts between angles would look smooth as silk.

             

            I realize now I should have borrowed 3 other cameras, and shot all 4 angles simultaneously.
            • 3. Re: sync multiple video tracks: same action, shot at different times
              the_wine_snob Level 9

              I've been trying to come up with things that might help, but even multi-cam in PrPro would not help, since we have 4 performances per position. It's really too bad that the audio was not being played during the performance and recorded on camera. You could have used that to establish visual sync, and then eliminated it for the CD version, ripped to PCM/WAV.

               

              Since you obviously know the positions, you are ahead of the game. I'd say to manipulate it, until you are happy, and then only a master might pick up a tiny OOS (sync of the visuals here) issue.

               

              Before you just cut things apart, I'd start and see how things go. When you do need to make a cut, that can be used to re-sync, and to apply more/less Time Stretch.

               

              Things might be closer, than you think. Also, remember that an audience cannot and will not focus on both PiP's at the same time. Really close might be everyone else's "perfect."

               

              I wish you luck. Going back decades, I had to shoot an open heart surgery from outside the OR. I did get my sound man inside, and he recorded two hours of wild sound. I was behind a glass, shooting, and there was no way to run a cable for the sync. I feared editing that shot. Early on in prep, I found the surgery nurse opening a sterile pack of instruments. They were wrapped in cellophane, and I found the audio for that operation. In 5 mins. we had sync on that. We just ran the film and tape, and sat in amazement. Everything was in sync. When I changed magazines, the sound guy must have changed tapes. The entire two hours was in almost perfect sync. Now, we did not have many closeups of the team, and they were all masked, so there were no frame filling lips moving, but we left the editing booth about 10:00PM and went drinking. We'd budgeted 2 - 3 days to handle that footage! Now, only about 45 sec. appeared in the final cut of the film, but we had all of for the director, and were very satisfied. She knew of our problems getting all of the gear inside the OR, and we'd primed her of how tough it might be. She assumed that we'd sneaked a sync cable past the bio-tech people, and did not get caught. I wish you even more luck, than we had.

               

              Hunt

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              • 4. Re: sync multiple video tracks: same action, shot at different times
                trevorrotzien Level 1

                Hunt,

                 

                Thanks for the feedback (and the great story, BTW).

                 

                It looks like I'll simply have to bite off time-stretching across the 4 tracks for each of the 24 forms. I may learn a short-cut along the way. (The next batch of Tai Chi footage is for an 88-form routine!).

                 

                Trevor

                • 5. Re: sync multiple video tracks: same action, shot at different times
                  the_wine_snob Level 9

                  Trevor,

                   

                  Look upon this as a "learning experience" working up to the "feature film." If you do discover any shortcuts, or enhancements along the way, please do share them in this thread - you will educate me, and will help others in the future. In the past, I have used cut-away shots, but that will not help in your particular case.

                   

                  Still have not come up with any thoughts that might help you.

                   

                  Good luck,

                   

                  Hunt

                  • 6. Re: sync multiple video tracks: same action, shot at different times
                    trevorrotzien Level 1

                    Thanks Hunt.

                     

                    Definitely a learning experience, and however this turns out, I will post what I actually did, with any tips, tricks or traps I encounter.

                    • 7. Re: sync multiple video tracks: same action, shot at different times
                      the_wine_snob Level 9

                      We'd love to see the final output, and your steps to achieve the final. Those will very likely help others in the future.

                       

                      Great luck - sounds like a very interesting Project!

                       

                      Hunt