Discussed recently.

If you consider changing intermediates Magic YUV RGB and UTVideo rise to the top.

XAVC-I works well, but not lossless. Neither is MJPEG

Thanks for the suggestions! MagicYUV looks quite interesting. Unfortunately it doesn't really give me a file size advantage over Magix Intermediate. One of the things I like about MJPEG is it's small size for high subjective visual quality. A jpeg at 95-100 quality is almost indistinguishable (visually) from lossless.

I'm shooting on an entry-level DSLR and editing on a laptop. My camera spits out an interframe-compressed video that's maybe 40MB for 10 seconds. With MJPEG, that grows to maybe 60-80MB, a very fair tradeoff. With MagicYUV or Magix Intermediate, it's more like 300MB. That type of file size inflation is the result of an excessive level of detail relative to the source, in my opinion. It's like making a WAV from an MP3 - you don't actually gain any quality, you just render the artifacts more accurately. If I were shooting in 10-bit or at a very high bitrate I'd see the benefit, but in this case I don't.

I see mention in one of the threads john_dennis linked that Morgan MJPEG can work with Vegas. I'm hesitant to spend money on an MJPEG codec in Anno Domini 2019. Perhaps I will try ffdshow and report back. Or, alternatively, even all-i-frame h.264, which sounds insane but would still be better than what the camera produces natively.

If you install a codec pack like ffdshow, you may lose the ability to open some native file formats in Vegas that worked previously.. We cannot help you with that here except with the preemptory advice not to do it. Goes double for k-lite.

A really sweet lossy intermediate is UT422.

Rather than a lossless intermediate, would a smaller proxy like 720p mpeg-2 serve your purpose? You just swap them out with the originals at render time.

Oof, thank you for saving me from that nightmare, I wasn't aware those codecs would overwrite existing ones.

Using a proxy is a good idea, but I'd like to be able to use stabilization. I'm shooting on a monopod and sometimes I like to pivot it around for slider-like or jib-like motion, and the stabilizer helps keep the motion constant. Stabilization from a proxy wouldn't "transfer" to the original clip at render time, would it? What about clip fx like color correction?
Thanks again for all your help as I try to squeeze a good workflow out of this setup.

That I did not know, since I've done proxies manually for about 15 years. I no longer have production demands, so there are a few things in Magix Vegas I need to look at and learn.

Thanks again, Eagle Six.

"What's new in version 13.0: A new Automatically create video proxies for Ultra HD media setting on the Preferences > Video tab allows you to choose whether automatically create video proxy files when adding 4K video to your project." (Online Help file "Creating proxy files for high-definition editing".)

Thanks all for your help. The proxy feature works like a charm