how do I convert .iso to .mp4 without mounting with ffmpeg
Solution 1:
You can do this with Handbrake, which comes in both GUI and CLI flavours and uses ffmpeg on the backend to do the transcoding.
HandBrakeCLI -Z "High Profile" -i a_movie.iso -o a_movie.mp4
Alternatively, if you have some funky FFmpeg voodoo that you can't easily replicate in HandBrakeCLI, you could mount the ISO locally and copy the VIDEO_TS folder up to the server that you want to do the conversion on.