Please let us know which Canon camera you're having issues with recording video. Are there also any error messages that appear on the camera's LCD screen? What type of memory card are you using?
For high definition video (HD), we recommend on using an SD card that is Class 10. We also recommend to format the memory card inside the camera prior to recording with it. Please check the box "Low level format" if available in your camera's menu for formatting the memory card. Please note that formatting a memory card will erase all data from the card.