I think maybe I can contribute to this thread, but I'm not sure if I'm contributing to the original question or the answer.
I've been outputting some .MP4 videos from PowerDirector (using H.264, not H.265) and my results seem similar to Isak's when I try to get the videos over to our HDTV, using either of two methods: 1. dragging the file into iTunes on my PC, then trying to stream that with Apple TV, or 2. copying the file onto an extrernal hard drive and connecting that via USB to a Micca Speck video player that's connected to the HDTV.
In both cases, the video plays and seems to be working, but attempts to fast forward, or more particularly, to use controls to jump to a particular part of the video, cause weird problems. (like the video freezing, or playing but losing its audio)
Having given that long description...
What seems to work for me (although I'd welcome a better system) is to output the H.264 MP4 from PowerDirector, then use another program (VideoReDo) to perform an action on the video called "QuickStreamFix."
I'm not even 100% sure what QuickStreamFix does, but it seems to involved fixing keyframes or something like that.
Once I run QuickStreamFix on the video, it then plays perfectly, whether I use my Micca Speck or my Apple TV.
It seems that by default, PowerDirector outputs a video file that doesn't work quite right with my devices, but doing *some* kind of post-production fix makes it right.
I hope this extra detail helps in some way.