you can submit blob to the backend in real time via ajax

Video works the same as audio. Here, take audio as an example.

in fact, this problem you need to negotiate with the backend, assuming that there is an interface to accept file streams in the background, then the code looks like this:

navigator.getUserMedia(
            // constraints
            {
                //video: true,
                audio: true
            },
            // successCallback
            function (localMediaStream) {
               fetch(url, {
                   method: 'POST',
                   body: localMediaStream
               })
            },
            // errorCallback
            function (err) {
                console.log("The following error occured: " + err);
            });
    } else {
        alert("getUserMedia not supported by your web browser or Operating system version");
    }

Brother, have you solved your problem? I have the same problem