Extract audio track from video, or "how to extract sound from video" WITHOUT CONVERSING?

Question

Video processing

1. Separate audio from video (no conversion)
2. Convert audio
3. Replace original AC3 audio with MP3 track (no video stream conversion).
Is it possible to implement it somehow?
Ps My TV does not support the AC3 format (the most common in films posted on trackers in 720p format), but I want to watch it on a big screen.

Answer 1

man ffmpeg
1. Separate audio from video (no conversion)
Use to get audio track without video
2. Audio convert
Convert one encoding type to another
3. Replace original AC3 audio with MP3 track (without video stream conversion).

ffmpeg -i input_file_with_mp3_audio.mp4 -c:v copy -c:a libfdk_aac -b:a 128k mp4.mp4