To confirm or rule out... specs on the card you are using? Quality of the video is directly tied with the speed of the card used... also be careful when looking up specifications... usually quoted right up front is a parameter that for our application, is pretty much irrelevant... read speed.
Deeper in the specs is what you are looking for... write speed. Also note that what is quoted is usually the "maximum" write speed... your sustained write speed may be only ½ of the quoted number. A quoted write speed of 90 Mb/s or better is ideal. A newer parameter of Video speed is a good indicator of a card well suited for video file writing. Video ratings show as V30, V60 or V90.
If perchance, you are using the supplied 16GB card that came with the system... as you have seen, that one is not fast enough for quality video. It should be primarily used for FW updates.