Okay
Crowley9, I've been thinking about this some more, and I've come up with a possible solution.
Here's a proof-of-concept, the two GDVs that first play when RotH launches, at 320x400 instead of 320x280:
https://www.dropbox.com/s/luygjhmehykjfd5/GREMLOGO.zip?dl=1 (155mb)
I know there are a couple of glitches here. When the title appears, some pixels that should be white are turning black instead, and it looks like there's something flickering towards the bottom of the screen at regular intervals. I'm not sure why this is, yet, something's going wrong with the decoding/re-encoding. I need to do more investigation on that.
Also, the files are much bigger now, e.g. INTRO.GDV has gone from 88mb to 528mb. I can probably improve this too.
But otherwise, does this look like you would hope it would look? Let me know.
The trick that I used was to double the frame-rate, from 12fps to 24fps. The "odd" frames (1, 3, 5, etc.) draw about half the image, but do not get displayed when the video is playing. The even frames (2, 4, 6...) complete the rest of the image started by the previous frame, and then display it. It seems to work pretty well, and gets around the problem of limited space for compressed frames.