It's possible that you're simply overtaxing your system. Even an extremely powerful computer is going to choke a bit once you get half a dozen videos playing at once.

It is also possible that you're having a problem mixing formats. You don't say how each person recorded his segment, but if one person recorded on a Samsung phone, another on an iPhone, another on a webcam and another on something, that's a lot of different resolutions, frame rates and codecs, which is going to tax your system even more.

Here's my tutorial on creating this effect. I shot all four segments with the same AVCHD camcorder, which minimized this issue. But if I'd have tried to do this with twice as many videos, I'd likely see some choking too.

Try outputting a segment of your video to see if the issue will be in your final output or if it's only a playback issue while you're editing.

Thanks, StevenG, for your message. I don't believe it's a problem with over taxing my system. I've built the PC within the past year and have created 10 virtual choir videos in that time. My most recent video utilizes over 50 singers and instrumentalists. The problem only occurrs with certain individuals. And has reoccurred with some of them over the course of several projects, so I believe it's specific to the individuals' videos. I have no control over anyone's camera/phone settings. So if it's a frame rate issue, is there a frame rate for the project which will minimize or eliminate this from happening?

If you go to the 45 second mark on the above link, you'll see a bit of it with the violinist in the lower left hand corner.

Jim PowerDirector 365, AMD Ryzen 7 3700X 8-core processor 4.05 GHz, 32GB RAM, Windows 10 64-bit OS, NVIDIA GeForce GTX 1660 SUPER

It's really not so much the timeline frame rate, but more source and produce. For instance, one can have NTSC 59.94fps source, drop it into a 24fps timeline, and produce to a NTSC 59.94fps profile and actually use SVRT (no encoding) as source matches produce. What will happen is some frames in the timeline will not be displayed as I need to get from 59.94 to 24 during timeline playback since I specified 24fps timeline. So if I wanted to create a snapshot at some particular frame that was available in my 59.94fps source, it may or may not be available with my timeline settings.

In your case, since getting source from:
a) many people and various video complexity
b) and the fact that most phones can create video in a highly variable frame rate depending on scene complexity
c) and the fact that most phones can create highly variable bitrate videos
d) and coupled with the fact that each contributor really only fills less than maybe 1/5 the produced product frame resolution

I'd preprocesses each source video to a smaller framesize (maintaining aspect ratio) at the final produced product frame rate you desire and simply make sure you produce to high quality video bitrate and audio at the same desired frame rate. So basically a fixed frame rate and bitrate which is usually video PD works extremely well with.

Jeff

Thanks, JL_JL, for your message. When you say reduce a video to a smaller framesize (maintaining aspect ratio), do you mean simply drag a corner in the preview area, or use the Scale sliders in the PiP Designer? And then produce it at the same settings I plan to produce the finished video, say MPEG-4 4K 3840 x 2160/30p (50 Mbps)? That individual video would no longer fill the entire frame, but have a lot of black background around the musician's video. Or is there some other way to reduce the framesize that will still fill the entire frame?

Thanks,

Jim PowerDirector 365, AMD Ryzen 7 3700X 8-core processor 4.05 GHz, 32GB RAM, Windows 10 64-bit OS, NVIDIA GeForce GTX 1660 SUPER

Quote Thanks, JL_JL, for your message. When you say reduce a video to a smaller framesize (maintaining aspect ratio), do you mean simply drag a corner in the preview area, or use the Scale sliders in the PiP Designer? And then produce it at the same settings I plan to produce the finished video, say MPEG-4 4K 3840 x 2160/30p (50 Mbps)? That individual video would no longer fill the entire frame, but have a lot of black background around the musician's video. Or is there some other way to reduce the framesize that will still fill the entire frame?

Thanks,

Jim

I think you totally misunderstood the point or reason for doing the approach I suggested. No, it makes no sense to resize a clip and then produce at your end target frame size of 3840x2160 and have all the black and use that in timeline to simply trim again.

My point was, since you have these judder issues, it's probably best to take all these random clips from everyone at random variable frame rates and random variable bitrates since most are phone source related and create constant bitrate and constant frame rate as PD usually works very well with that. Consider HandBrake or the like for that task. PD often does not work well mixing highly variable frame rate source files. Since one has to do that step and adsorb the cost of 100% encoding, you might just as well put each in a smaller frame resolution, say 1280x720. Based on glancing at your production, each source at best occupies a small region of your end produced 3840x2160 frame resolution, take advantage of that during this preprocess stage to lower the overall editing and/or producing demand.

Jeff

Ok. Yeah, not having done that, it's not something I'm familiar with. But I'll look into HandBrake and see what I can learn. Thanks.

Jim PowerDirector 365, AMD Ryzen 7 3700X 8-core processor 4.05 GHz, 32GB RAM, Windows 10 64-bit OS, NVIDIA GeForce GTX 1660 SUPER