Error

I guess you could check the size of the lossless and lossy frames it outputs, to convert the fps to Mbps. If both values are similar then it's probably the drive

I just did a rough calculation where I did estimated size of png / estimated size of jpg * fps of png and the value was roughly in the ballpark of what the fps for jpg were, so I'm very sure it's the drive

I additionally use these to get much better JPEG quality:

  • -qmin 1 -q:v 1 -huffman optimal