Unless you are specifically using SheerVideo for streaming over the Internet, you must uncheck the Prepare for Internet Streaming box. In the standard QuickTime user interface, this is near the bottom of the Movie Settings dialog box.

SheerVideo is intended for uncompressed-quality professional video and film production and archival. The Internet Streaming option, in contrast, is tuned for distribution over very low-bandwidth channels, and greatly slows down SheerVideo playback.