Just as for images, Craft will not convert or compress the original size of video files. You can upload any format of video into a Craft document.
Some of the most widely used video formats, such as .mp4 and .mov, will present a thumbnail preview, while other formats like .avi, .wmv, and less commonly used formats will be displayed as standard attachment blocks:
Playing Videos
Any video file with a thumbnail preview will be opened in a separate player:
Video files presented as standard attachment blocks will need to be downloaded first, then played with a compatible program.
Note: Craft does not yet have an embedding feature for videos.