5D Mark III Photograph vs Video Quality
5D MkIII video limitations
5D3 video performance has been frequently criticized for low resolution and unsharpness. It has been mentioned by various people that the vertical resolving power of 5D3 is closer to 720 than 1080 - even if you shoot at the highest resolution possible. There isn't much you can do about this. The blurriness can be corrected to a large extent by sharpening during post processing - as suggested by Philip Bloom.