Project bigtime failing to export

Windows 10.0.19045
Shotcut 24.06.26

Long story short, neither VP9 or NVENC can get this to work. The artifacts are very similar to when I tried to use libx264 and libx265 on projects using time control filters. I’d get those artifacts on the simplest projects using libx, like a video with one clip and 3 time filter keyframes. But so far it’s only been user error messing me up with VP9, and NVENC has always worked. So… now I just have no idea. I tried exporting this thing about 10 times, and sometimes its a little different, but most of the artifacts are the same. There’s one clip used as an overlay that’s playing at 5-8x speed; it becomes a 2x4 grid of blue pixels. Then there’s the artifacts I saw with software encoders: clips used as overlays become white and grey checkerboards. Then several other clips are way out of wack with playing back what theyre supposed to. They play the wrong part of the clip theyre supposed to come from. And then my main video in the background is shooting around to the wrong parts, probably at the points where I cut the clip. Then some stuff is just missing, moreso in certain exports than others. Idk man it might be helpless and I might have to just lose who-knows-how-many hours of work on an old ass save, but I just have no idea where to start with saving this. I tried both the limited and full color ranges, 1440p and 4k, a whole bunch of reasonable settings for VP9, aac instead of opus, 264 and 265 NVENC at 12MB/s

shotcut nvenc fail.txt (1.8 MB)

I got nothin man. Sorry for being a pain, love u guys

There is a lot to unpack from your story. I wonder if there are multiple problems colliding.

Regarding the artifacts, can you share a screenshot to show what an artifact looks like? Do they appear in the Shotcut preview or only the export?

Regarding VP9/NVENC, can you try a regular export using the default MP4 export preset (disable hardware encoder, and and do not change anything in Advanced). This test could help narrow down if you have an export problem.

I can’t help with the artifacts, but what device is the original footage taken on? That sounds like it could be a variable frame rate issue that often only manifests after you start trimming or cutting. From my own personal experience that is also enough to cause an export to fail. I would start by converting those to edit-friendly and re-test, although you may also need to redo the cuts that are now out of whack.

Is it safe to assume you started the project on the same version of Shotcut you are working with now, and there was no upgrade mid project?