Thanks for the note and I wanted to give some more details. The screen recorder on classic Stream and the new enhanced screen record on stream.office.com are using the browser to generate a video file. Currently the browser support creating .webm files so that is what is outputted when you all use the recorder. There are currently no plans to change the file format as it plays back in classic Stream and on Stream on SharePoint. I do wonder why folks are needing another file format.