I tried to figure out a fix for this but nothing seemed to work. Things that didn't work: updating thunderbolt drivers, updating video cards' drivers, disabling the internal gpu, disabling vsync, lowering the resolution, etc...
The only thing that did work was to re-encode all the video files to 1920x1080. Which is fairly easy to do and takes about an hour. If anyone else wants to do this:
1. Download and install RAD Video Tools: http://www.radgametools.com/down/Bink/RADTools.7z (You'll need 7-Zip to extract: https://www.7-zip.org/a/7z2103-x64.exe)
2. Open RAD Video Tools and navigate to the directory: "C:\Program Files (x86)\Steam\steamapps\common\Mass Effect Legendary Edition\Game\ME1\BioGame\Movies" or where you have it installed. You might also want to copy these files and back them up somewhere.
3. Select all the files then click "Bink it!", click "Yes" to "...batch process them one by one...", leave all the defaults except enable "Automatic overwrite?" and change (under the "Scaling type..." button) "Width" to 1920 and "Height" to 1080. Screenshot of my settings attached.
4. Click the "Batch" button and then click the "Start" button. Go grab a beer and wait.
I also tried different encoding settings but nothing seemed to work except changing the resolution to 1920x1080. Other things I tried was: keeping the files 4k but lowering the bitrate, removing the audio, increasing the audio compression, and lowering the resolution to 2160x1440.
I finished ME1 with the resized pre rendered cutscenes and it worked great. I'm onto ME2 now which has even more cutscenes to convert. I used the same RAD Game Tools settings as ME1 except it appended "New_" to all the rerendered files. If that happens to you just open a terminal in that Movies directory and run: rename "New_*.bik" "////*.bik"
