Replacing your hard drive with an SSD would be first step, if you haven’t already. Something like
this should do it. You may want to take the opportunity to increase the hard drive size to 500GB or higher at the same time if budget allows to make room for all those big video files.
Doubling the memory would be the next step. According to
EveryMac you can put 8GB of ram in there, so one of
these will max it out. You may be able to get the MacBook to recognise 16GB of ram (
2x8GB SO-DIMMs) if you want to take the risk.
IFixIt have details instructions on replacing both the Hard Drive and RAM.
Good luck