The 1.3 versions of Audacity (with the ffmpeg library installed ) will rip the audio from an MPEG4 video.
I suspect combining the modified (amplified) audio with a copy of the original video images will require a video editing programme, (Audacity only edits audio , i.e. edits sound not images).
https://forum.audacityteam.org/t/editing-audio-from-a-vcd/15073/9