Forking is not that much a problem when it's limited to a program. Typically in the case of MPlayer, you had mplayer2, and nowadays mpv, and this is fine really. It's just a program that could live with the others without much trouble.
On the other hand, with a project like FFmpeg which actually provides libraries, it can really hurts the users community. Especially when the forking is made without changing the library names... which is exactly what happened here (thanks to the confusing name of the fork, chosen on purpose).
Basically, the fork was made such that only one can survive (example: only one "libavcodec" can exists), because they were actually confident about the outcome. But it seems they didn't anticipate such fundamental changes in the way FFmpeg continued to live.
On the other hand, with a project like FFmpeg which actually provides libraries, it can really hurts the users community. Especially when the forking is made without changing the library names... which is exactly what happened here (thanks to the confusing name of the fork, chosen on purpose).
Basically, the fork was made such that only one can survive (example: only one "libavcodec" can exists), because they were actually confident about the outcome. But it seems they didn't anticipate such fundamental changes in the way FFmpeg continued to live.