Nikolay Sivov (@nsivov) commented about dlls/mfmediaengine/main.c:
engine->playback_rate = 1.0; engine->volume = 1.0; engine->duration = NAN;
- engine->next_seek = NAN; engine->video_frame.pts = MINLONGLONG;
NAN was used for duration as a special marker because it doesn't come from user input. For the "next_seek" we could use another flag probably, instead of relying on this special value. Let me know which way looks better to you.