The .MTS extension refers to files of the type AVCHD video files. These are advanced High definition MPEG transport stream files.

These files are mostly created by the High definition video recording cameras like Sony,Panasonic etc. The file format supports both HD (720p) as well as true HD (1080p) or fullHD as some people call it. AVCHD is nothing but a codec for video format whose full form is Advanced Video Codec for High Definition.These files may not open natively in the popular media players but are ususally editable and can be converted to popular video formats using the software that usually come with the recording cameras.