New version 1.4 in first post. Much better balance between vsync and frame dropping, for when background tasks take too much time. This can be things like collection indexing, phoning home, switching to screensaver mode, etc.
Occasionally, the eink drivers can get so far behind that the video quality degrades badly and cannot catch up until the video ends. In that rare event, just stop the video and restart. I may add a feature to automatically pause the video for one second when we detect this "too far behind" condition. Version 1.4 does not check for that, but gets all the other interruptions under control rather nicely with its frame dropping mechanism. In fact, on the K4main hybrid video mode, the sample video "normally" drops about 100 frames, and I cannot even see any jerky motion to show where they were dropped.
This version 1.4 supports all eink kindles, about as nice as it can. We get this video performance by updating the eink about 2.5 times faster than the book says to, and ignoring any "not ready" status reported by eink update calls. Instead, I use software tuning, and I think we have that just about at the right balance to work better than expected for all kindle models.
For me, the results on this little project FAR exceeded my own expectations for this limited hardware. I think I proved that the kindle can be a useful live video platform, provided that the video is tuned to be eink compatible (reduced contrast for fast moving objects, only very slow camera panning, spatiotemporal video smoothing, and other controllable video content adjustments to enhance quality and reduce unwanted visible artifacts