I've been watching HitFilm closely for years, because the idea of a all-in-one After Effects+Premiere+Element3D replacement really feels right.
The Compositing part of HitFilm 4 is really amazing. I'm really impressed. The last update, with Maya-like controls of the 3D viewport is really a slamdunk. I'm almost ready to leave Adobe...but I can't because the Editor in HitFilm is UNUSABLE.
Since version 2, I always download the trial version and do a simple test: a simple edit, with 5 clips and 4 cross fade transitions.
EVERYTIME the software is slow (slow and choppy playback during the cross fades), so I give up and wait for the next version. Yesterday I've tried the last version f HitFilm 4. And the software is still slow.
I've tried different codecs: H264 and AVCHD directly from the camera, DNxHD and Cineform. It was slow in ALL of them.
My computer specs: i7 4790K (4Ghz), 16GB RAM and a GeForce 970 4GB.
There is no reason HitFilm 4 can't play a basic transition in realtime with this setup. I did the same test in Premiere CS6 and Resolve, and they work flawless. In Premiere even 4K footage play in realtime, and we are talking about the CS6 version, a 5 year-old software.
Heck, even Final Cut Pro 7 (a 32 bit application) in my old Macbook plays it ok if I transcode to ProRes
So, I really, really, really want to love HitFilm 4, but right now the Editor is basically not working.
I'd suggest to basically fix this before ANYTHING in the next update.
As a short term solution, we should have the option to pre-render the timeline in the editor. Most NLEs let you do this (Premiere, the Old Final Cut, etc...). Right now you can only RAW preview in the Compositing mode.