From Jacek Pazera:
Pazera Free WebM to AVI Converter is the freeware application which converts YouTube videos (WebM, MP4, FLV, 3GP) to AVI or MPG (MPEG-1, MPEG-2). WebM is an open media file format designed for publishing videos on websites compatible with HTML 5 specification. WebM files are commonly used by many websites, including YouTube, Wikipedia. Unfortunately, many players and video editing programs does not support WebM. In this case, it is necessary to convert WebM files to more popular format, such as AVI or MPG.
The basic usage of the program is very simple: just drag & drop video files into main window and click the CONVERT button. More advanced users can customize the parameters used by encoder: audio and video codec, audio and video bitrate, fps, sampling frequency, resolution and other.
At default settings, the application automatically selects all the encoding parameters so as to preserve the original video and audio quality.