Sorry for my bad english, I'm french and I am only 13.
So I installed your snapshot of the Replay Mod, and I have correctly installed ffmpeg (In Program Files(x86), I used the batch file : https://replaymod.com/files/ffmpeg-path-installer.bat).
Unfortunaly, when I try to export my replay, it tell me "You need to have ffmpeg installed". (I restarted Minecraft several times).
Windows 10 64bits
Other mods : Modpack Sevtech Ages + Optifine + Bauercam + Mycommands + ReplayMod (snapshot of this thread : https://www.replaymod.com/forum/thread/2489 + CustomMainMenu)
Thanks in advance for the help !