I think the idea of two proxy presets is brilliant. Ut Video is mathematically lossless, and using it along with 480x270 could be a useful preset for people stacking a lot of tracks, which requires low resolution to composite everything in real-time. (My personal stack record at 480x270 is 18 tracks.) The second preset could be 960x540 using H.264 All-Intra to save on disk space. I haven’t tested the lossy codecs as thoroughly for this second preset, so another one may end up being better. But H.264 All-I would be my start point for research.
(To be super technical, all that really matters is the height when deciding the proxy size. My ffmpeg scripts use
-vf scale=-1:270 which means “video filter scale to whatever width correlates to a height of 270 pixels when preserving the aspect ratio”. This way, you always have 270 or 540 lines available to your preview window, but the width is free to jump around in case somebody brought in a video of a digitized 4:3 VHS tape or something. Not every source is guaranteed to be 16:9, so only the height is constant among proxies.)
As a general principle, there isn’t much benefit from a 1080p proxy, especially lossless. The phrase “full-resolution proxy” is literally an oxymoron. A full-resolution transcode, if lossless, is an intermediate rather than a proxy. A full-resolution transcode, if lossy, is not perfect anyway, so why overkill the resolution on such imperfection?
960x540 is a bit of a sweet spot for people editing on 1080p monitors (which is probably the majority of people at the moment). At 960x540, the video is slightly bigger than the Shotcut default preview window, which makes for a fast and sharp preview. It is also half of the monitor’s resolution when going to full-screen, so it will scale perfectly and still look decently sharp for editing work at full-screen. If the proxy was 1080p, the preview window would have to scale the video down to fit (which takes CPU), the compositor and all filters would have four times as many pixels to smash together (more CPU), and the full-screen preview would provide a level of detail that gains you nothing in terms of functionality over 540p. There is also the extra encoding time and disk space required to make the 1080p proxy. It’s extra work for no added benefit if using a 1080p monitor. Proxies by nature are supposed to be imperfect so they can be fast. Sensitive work like color grading can be done after switching back to the originals.
Granted, everyone’s preferences and unique project requirements are different, but that’s the general principle and a pretty good starting point.
Oh, almost forgot… using Ut Video…
4K source to 480x270 proxy = proxy at 40% disk space of source. The start resolution is massive and the proxy resolution is tiny, so the relative space percentage is small.
1080p source (25% of 4K) to 1080p proxy = proxy that takes more space than there are atoms in the known universe. The start resolution is small, the proxy resolution is high for a proxy, and it’s lossless, so the relative percentage is going to be well over 100% (as in, proxies will be significantly larger than the sources).
BTW, you qualify as a technical person if you can make sense out of any of the mumbo going on in here.