I have some videos that are recordings of myself playing the piano, and I have converted them into mp4. It is no suprise that video files are often large, but I don't care visual resolution, and just hope that audio quality may be kept as close to the original as possible. My understanding is that in a video, visual information makes up most of the file content, but it is audio that I mainly care. While I also want to share the (visual) video with friends, so a medium or low quality of (visual) video is acceptable.
Here, I used Total Video Converter Lite to convert them from "High Quality" mp4 to "Low Quality" mp4. The converted files do occupy less disk space, having also smaller width and height in terms of pixels. I have compared the original audio and the compressed one, but find them very similar, or perhaps the same.
How to make sure that the video compression only makes visual quality inferior, while retaining audio quality? Is this difficult or not? Or perhaps I am already doing it? Are there some standards of video compression so that I know which one is that?