Well, I've read some posts here on the same issue, but still can't pin point the exact issue, although I'm thinking maybe its a result of different frame rates.
I'm not a professional editor, but I've been working on a music video of mine, which has combined a lot of footage from everywhere. Three main cameras to shoot the band (RED CAMERA shot in 4K, Canon and a Sony all shot 1920 x 1080 and all at 23.976 fps). Plus a collection of over 200 random videos in different resolutions and frame rates ranging form 23.98 to 60.00. My sequence is at 1920 x 1080 becuase 90% of footage is shot in 1080 or 720.
Created proxies for everything in my sequence because of choppy playback. Created a custom proxy setting (Cineform 1280x720) based on a YouTube video, which took forever. Believe it or not its worse than without proxies. While not using proxies, it can sometimes go without issues from beginning to end, 5 minutes total, with slight lag, usually in the 4K shots. But when proxy is on, its a nightmare. I haven't even put effects to the clips aside for some scaling adjustments, because I can't view a simple beginning to end flow of the video and can't properly guage where a specific effect needs to go. Quite frustrating as you can imagine.
Is this simply a frame rate issue? Any help would be appreciated.
I was thinking it might be a horsepower issue and been debating upgrading my Late 2014 Mac Mini to a newer one.
In regard to proxy files, I created them by creating first an encoding preset in Media Encoder, Format -> Quicktime ->GoPro Cineform YUV 10-Bit (Audio/Video Checked). Basic Video Settings - > Quality 1 -> Width 1280 Height 720, Frame Rate -> 23.976, Field Order -> Progressive, Aspect -> 1:0 (square pixels), Render at maximum depth not selected, Depth -> YUV 10-bpc, "Use max render quaity" unchecked, Effects -> I added an image overlay to distinuish between proxies and original.
Then created ingest preset: Transfer-> checked "Transcode files to destination"
Format - > Quicktime, Preset -> The one I created
Then in PP, I created the proxies of all my footage by selecting the ingesting preset I just created.