massive number of dropped frames with AVC MP4

Comparing a simple video player with an NLE is actually a rather absurd thing. They both play back video ... but then, cars and ships both travel somewhere. Also as close to each other as players and NLE's.

The player isn't combining bits of clips here and there, throwing in effects & other things, all that sort of thing an NLE does. If that media isn't intraframe (which the above mentioned Cineform, and also DNxHD/R would be), it's long-GOP.

Meaning the camera records one complete frame, then a bunch of matrixes for the next 15-30 whatever frames, listing the pixels that change and how they change. To de-encode that, the CPU grabs the first frame, de-encodes to a "real" frame, sends that to RAM, pulls up the matrix for the next frame, recalls the complete frame from RAM, compares the two & makes changes, storing that frame & sending it down the line ... recalls the matrix & frame from RAM, makes a new frame ... on and on. It's a very intensive, core/thread/RAM process.

It's bad enough with "Full HD" or 1920x1080 ... but you're throwing 4k at it. With several times the number of pixels to de-encode.

This is why you don't see a problem with "better" codecs.

You think this is a problem in PrPro, you should talk with some of the colorists I know ... massive rigs to run Resolve in real-time, then they get a long-form project that's got a lot shot in long-GOP 4k. And their massive spendy computer slows to a crawl. Yup.

That stuff's just hard on a computer. Easy on camera cards, but ... hard on an NLE.

Neil

I recommend using Cineform Proxies with all H.264 media.  The editing performance is significantly improved.