Unlike YouTube, Screencast.com does not transcode your video, so the video format used on your Computer will be the same when uploaded to Screencast.com.
MPEG-4 or MP4
The MP4 video file format encoding using H.264 video and AAC audio. TechSmith products such as Camtasia Studio / Camtasia for Mac and Snagit produce MP4 video files using H.264 encoding, are played back using our HTML5 player, which will fall back to Flash if HTML5 is not supported.
Non H.264 encoded MP4 files may upload, however the are not officially supported. You may notice playback requiring Adobe Flash Player, QuickTime, or the video may not play at all.
For more information about file formats and Screencast.com please visit this Tutorial Article:
File Formats that can be Embedded on Screencast.com