Some DS games use the DMA hardware to read ROM data asynchronously (where the CPU can't), which as a result, allows game code to keep running at the same time the data gets read from the ROM.
They asked about the card read DMA setting in akmenu-next, not running 3DS games or unlocking anything in GBA games.
Did you mean to post this in a different thread?
Development on GBARunner3 is paused, as the developer is currently working on DSpico stuff. It may take a while before they get back to working on GBARunner3 again.
You need an old version of FFmpeg (v7.0.2).
Follow these steps here to install it an convert the video: https://wiki.ds-homebrew.com/ds-index/videoplayers#mpeg4player
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 25-30 seconds (depending on the video's aspect ratio).