and I have no way of obtaining that footage on my own.

I have the game. I have the software.
But my potatoPC can't run both at the same time. ;-;

forgot that gameplay needs sound effects but no music and I need gameplay of all zones.

idea: there is a PSP emulator ( https://www.ppsspp.org/ ) where you can run cave story as a homebrew (downloadable inside the emulator). This Version needs less ressources. i think your computer should be able to run this. but i don't know what a computer you have if it don't runs cave story.. even my computer which is not even be able to run minecraft without lags from hell can run cave story without lags. and i even have windows vista.. sooo normaly your computer should be able to play it without problems if your computer is not older than like 10 years. my laptop is REALLY REALLY old and can run it.. soo i don't know where your problem is here^^ which recording software you use? fraps?

i would do it, but i don't have a save file & i would need to complete the whole game / zones.. but never done that by myself so i guess i can't help you sorry. the game is rly long as far i know^^

well, i have a school restricted chromebook. sooooo i cant get emulators or screen recorders.

you could record it on your smartphone then :D ppsspp too runs there & there are good recording apps ("Screen Stream Mirroring" works fine).

bacically, my music idea is cave story zones, with music from the classic stages from sonic forces.
egg plantation= chemical plant
grass town= cassino forest.
sand zone= ghost town.
labrinth 1= egg man fight
labrinth 2= egg dragoon
outher wall= death egg
running hell= iron fortres
gravity= death egg robot phase 1.
thats why i needed it to be music less.

are you sure that you can't find gameplay without music @ youtube? should be a lot easier than recording & playing the game completly just for that^^

well i looked, but i couldn't find any gameplay without the music turned on.