While the old tests were nice in that they uniformly had keyframes every 5 "positions", and each GOP was simulated IPBBB, reading the related tests is a bit of a nightmare for those new (or returning after a while) to them.

This bug tracks refactoring those old tests to use a more modern style where the actual PTS, DTS, durations, keyframe status, etc are listed in "appends" as well as in the buffered range and buffer read test helpers' parameters.