Hello CallumBeau,
Sighthound Video has two types of data - "cache" or "temporary" video, and “saved".
Sighthound Video will record ALL video for a certain amount of time, you can set this in the preferences dialog - this is the cache. After the specified period of time has passed Sighthound Video will automatically trim the video and keep only the portions that matched rules with the "save" response. By default when cameras are added they have a rule "All objects in <camera name>" configured with the save response. These clips will be kept until either your hard drive is full or Sighthound Video reaches the disk quota set in the preferences dialog. “Saved” clips are then deleted oldest first to make room.
The video files you see is the cache video being saved. The size of these files will depend on the resolution your camera is streaming at. If you set your storage setting "Temporarily keep all video for up to: X hrs" to 1 hour, this cache video will only remain for 1 hour.
If you find that too much storage space is used by Sighthound Video, you can lower the "For clips and temporary video, use up to: X GB" option.
More details can be found here:
http://www.sighthound.com/support/managing-your-video