Version 15.0 Build 261 issue. I have 4K source video, then creating video proxy. With Video Preview in "Preview (Full)" mode, the system "flashes". Basically just misses frames and displays them as black instead.

Looking at the Windows system resources screen, I can correlate the problem with the computer not being able to keep up with file read speed, or possible with vegas "switching back and forth" between the mp4 and sfvp0 file.

I always see vegas reading the .mp4.sfvp0 file at around 4 MB/s. It also normally reads the corresponding .mp4 at around 800KB/s. In this mode everything is fine.

But at other times the .mp4 file is read at 30MB/s, at the same time that the .mp4.sfvp0 file is also being read, and that is when the "flashing" occurs.

My computer can handle 30MB/s, but isn't top of the line. (On a faster computer, the problem does not occur.) And Vegas is a bit of a hot mess when installed on a non-dedicated computer. I can see swap file access and other things causing performance to screw up.

But why is vegas reading that mp4 file in the first place? That is what the sfvp0 file is for.

Switch to "Preview (Auto)" and the problem goes away. (While reading only the sfvp0 file.)

"Good (Auto)" and "Good (Full)" are usually fine. (While reading only the mp4 file.)

What is even more peculiar is that the problem comes and goes. For example, I started this post because a particular editing session had become unworkable. But after writing this post and going back to confirm some things, it all worked just fine.

Bottom line, though is that something is reading both the .mp4.sfvp0 (4MB/s) and mp4 files in Preview(Full) mode (30MB/s), and the video preview flashes when that happens.