Whammy
A real time javascript webm encoder based on a canvas hack
...It exploits the relationship between WebP image frames and the VP8 codec used by WebM. Developers can add canvas elements, canvas contexts, or encoded image data as individual video frames. Frame rate can be defined globally, while individual frame durations can also be specified. Encoding happens when the collected frames are compiled, producing a Blob that can be displayed or saved as WebM content. The implementation is small and fast for client-side use, although its intraframe-only approach lacks the file-size efficiency of full interframe video compression.