I have been able to compile the most recent version of mpv with SDL2 + GLES2 backend. I used this configuration because mpvs wayland backend requires version 1.6 of wayland and SailfishOS currently ships with wayland 1.3.

but video playback does not work.

these are the current issues:
sometimes when i start a video this happens: https://bpaste.net/show/9609926e10ae
but sometimes it starts fine.. but the progress is not changing, the screen is black and there is no audio
if i press left/right or pause(space) and unpause(space again) it starts progressing automatically but there is neither video nor audio output
i have tried different file formats and file sizes but i had no success in starting a video yet.

the SDL2 errors i mentioned above happen independent of the file size at random.