Converting League of Legends Replay Files directly to standard MPEG-4 Video format (.rofl to .mp4 conversion) is, unfortunately, not possible. Game replays usually contain game engine instructions only, not recorded video data.
You could try loading your .rofl file (League of Legends Replay) in the game itself, and record the replay with a screen capture utility, such as Fraps or Camtasia. Then simply save the recording as an .mp4 file.Open ROFL file Open MP4 file
A screen capture and video editing software
A screen recording utility
A session-based, multiplayer online battle-arena video game for Windows