I have same problem.
This is a copy of a reply in other topic (How to record RAW digital cropped video in 5Dmk3):
My 5D3 doesn't crash but records weird frames randomly. Only with HDMI monitor attatched and in crop mode. My settings are:
5D3
HDMI monitor conected.
Komputerbay 1000x 64Gb
14 January 2014 build
MLV video
1920x1080
1920 30-I (in Canon menu)
Cropped mode,
16:9 aspect ratio,
Preview auto or Canon (the result of weird frames are same in both preview modes),
fps override 25,
Exact fps,
Frame skipping OFF
Global Draw ON (tested with global draw OFF same weird frames)
Image Quality = Raw
Auto Lighting Optimizer = OFF
Long exp. noise reduction = OFF
High ISO speed NR = OFF
Highlight tone priority = OFF
Multiple Exposure = Disable
HDR Mode = Disable HDR
I'm interested to know if someone can record cropped video without weird frames and a similar configuration (HDMI monitor conected).
If I disconect monitor all is ok. But dificult to get image in focus (cycling footage) with the in camera screen!!!!!.
UPDATED:
After extensive tests, I get random weird frames not only in MLV_rec.mo, also in RAW_rec.mo
Always with hdmi monitor connected and 3x crop video. Tested in 1920x1080!!!!
Weird frames are exactly the same as mhimhi shows in first post.
I see almost clear that is hdmi related problem. No monitor, no weird frames... So is a not enought cpu power in camera or not? Anybody knows?
Thank you very much.