OKIOCAM Snapshot and Recorder's default video format is WebM. This is because OKIOCAM Chrome extensions work within Google's Google Chrome web browser, and the default media file format for Chrome is WebM.
However, you do have the option of converting your downloaded and saved videos to other video formats, by using third-party video conversion software. We recommend Screencastify and Convertio to convert to MP4. There are other third-party platforms, such as VIP Video Converter (for example) that are able to convert to several other formats as well.