Well I can report its working on my end with a 3DS, got console boxes displayed for all my rom folders! Very nice. I just stuck them in the normal boxart folder in the _nds>twilightmenu folders and constrained them to the same dimensions as the...
Unfortunately, no (to both).
For movies, you could probably go down to 15FPS (or less) in order to reduce the amount of parts you may need. (Frames will be LZ77-compressed.)
Each part would be around 1 minute and 30 seconds.
Is the ".rvid" size reduced?
Possibly. Try reformatting the microSD card here: https://dsi.cfw.guide/sd-card-setup.html
If the issue persists, try a different video player here: https://wiki.ds-homebrew.com/ds-index/videoplayers
60FPS frames are stored uncompressed, interlaced, and in 8BPP (256 on-screen colors), the latter two to keep frame sizes as small as possible.
The longest 60FPS video you can have (while staying within the GBA ROM size limit of 32MB) is up to...
Try setting "BMP_MODE" to 0, then run Vid2RVID again. You should get a .rvid file at a reduced size (at the cost of color amount due to switching to 8BPP).
Please upload the .ini file from the frames containing the extracted video frames.
Also, what's the frame rate and resolution of the video (the latter from one of the extracted frames)?