RTCMultiConnection.autoSaveToDisk

This boolean is deprecated since RTCMultiConnection version 3

This boolean was used in RTCMultiConnection v2.2.2 and earlier.

Because v2.2.2 is no more maintained. That's why documentation for this boolean property is also removed.

Here is an alternative:

connection.onFileEnd = function(file) {
    invokeSaveAsDialog(file);
};

function invokeSaveAsDialog(file, fileName) {
    if (!file) {
        throw 'Blob object is required.';
    }

    if (!file.type) {
        try {
            file.type = 'video/webm';
        } catch (e) {}
    }

    var fileExtension = (file.type || 'video/webm').split('/')[1];

    if (fileName && fileName.indexOf('.') !== -1) {
        var splitted = fileName.split('.');
        fileName = splitted[0];
        fileExtension = splitted[1];
    }

    var fileFullName = (fileName || (Math.round(Math.random() * 9999999999) + 888888888)) + '.' + fileExtension;

    if (typeof navigator.msSaveOrOpenBlob !== 'undefined') {
        return navigator.msSaveOrOpenBlob(file, fileFullName);
    } else if (typeof navigator.msSaveBlob !== 'undefined') {
        return navigator.msSaveBlob(file, fileFullName);
    }

    var hyperlink = document.createElement('a');
    hyperlink.href = URL.createObjectURL(file);
    hyperlink.download = fileFullName;

    hyperlink.style = 'display:none;opacity:0;color:transparent;';
    (document.body || document.documentElement).appendChild(hyperlink);

    if (typeof hyperlink.click === 'function') {
        hyperlink.click();
    } else {
        hyperlink.target = '_blank';
        hyperlink.dispatchEvent(new MouseEvent('click', {
            view: window,
            bubbles: true,
            cancelable: true
        }));
    }

    URL.revokeObjectURL(hyperlink.href);
}