Shooting with a DSLR means you can have very large size images.
Some video formats have difficulty exporting large formats. If you are exporting animation and it is not working, please try the following:
File > Export animation
The Export dialog appears.
When the movie settings dialog box appears, make sure you set the dimensions of the movie to 1280 x 720:
At sizes above this, exporting video formats may not be reliable. For higher resolutions, try exporting still image sequences and importing them into your video software.