I want to create some song specific videos to song specific styles. From the research I've done to create a style I need to have a mp3. A lot of tunes are available as mp3's but some I can only find u-tube videos,
There is a software called AUDIALS 2022. That can grab the YouTube Video and load just the sound as mp3. Not sure if it can convert the video sound from a video that is already on a PC. But if you need the video anyhow, Audials is working fine. Their website claims that this is legal.
This is the simple way to extract audio from YouTube videos, not sure of the legality of it though.
https://yt5s.com/en54/youtube-to-mp3
Audacity can record the system audio and output as MP3 (as well as many other formats).
It is mostly not legal, but as you see by all the responses, it can easily be done. It all depends on the video and what the audio is as to the legality, but in most cases probably not legal.