I have always been a bit puzzled about how audio/video file formats work, and how the extension of a media file (e.g. mp4) doesn't always tell the whole story about what media formats the file contains and how it is encoded. I am starting to learn about the existence of container formats and codecs, and would like to learn this hands-on by looking at some actual media files.
A while back a friend showed me a program that can inspect a media file and draw a diagram of what is contained in the file. I remember these diagrams looked a bit like flowcharts. Does this ring a bell for anyone?
I am also interested if anyone has other recommendations for other good ways to learn how multimedia file formats work.