Playback AND the final export has horrible stuttering for some imported videos. I've spent hours experimenting with length, frame rate, and a few different formats.
One of the most common videos I make involve sourcing footage from YouTube, and that seems to be where I have the problem the most. However, it doesn't affect ALL YouTube videos.
In one test I did, I shortened a 6 minute video down to 14 seconds within Avidemux, then copied it to a new video file without re-encoding and it worked fine within Hitfilm. Since the video files are identical in all but length, this leads me to suspect some kind of performance bug with Hitfilm. [Avidemux did in fact change the frame rate mode in this example.]
Here's a demonstration I put together: https://www.youtube.com/watch?v=C-9MBObCAwU
Here are the source files from the demonstration: https://drive.google.com/open?id=0B_R_uP6zz0ReLXZYZ19Ta3F3M0E
Notice how the "Original YT" file plays fine in something like VLC, but not in Hitfilm's playback. [Unless of course it does, which would indicate something wrong on my computer's end.]
A practical example in one of my actual videos can be found here: https://youtu.be/HV8-QSATILY?t=1m42s
In the practical example, notice how smooth the spinning flower logo is at the bottom right compared to the choppy footage.
I'm pretty desperate to find a solution to this, but I'm afraid simply "convert all of your footage until you find something that works" isn't a helpful answer. Hitfilm should be able to work with h264.
GPU: GeForce 980 [Drivers up to date: 385.69]
CPU: Intel i7 6700K
OS: Windows 7
Hitfilm Pro 5.0.6718.7202
Thanks in advance for your help!