У вашего броузера проблема в совместимости с HTML5
This video shows how to enable or get stereo mix on Windows 10. You can fix stereo mix problems by downloading a codec.
Link to the RealkTek Codec
https://www.realtek.com/en/component/zoo/category/pc-audio-codecs-high-definition-audio-codecs-software
Please watch the new version of this video.
https://youtu.be/0smiTx8DC20