Why the old file failed: your screenshot shows Windows error 0x80070002. The browser/Windows player is trying to access the downloaded WebM file and cannot find/open it. This version keeps the recording inside the browser first and only saves the actual WebM file after recording is complete.

Important: The recording format is WebM. Do not rename .webm to .mp4; that does not convert it. Guaranteed MP4 requires a real conversion step such as FFmpeg.