问Recorder.js录制未按预期工作

EN

function startUserMedia(stream) {

            var input = audio_context.createMediaStreamSource(stream);
            __log('Media stream created.');
            // Uncomment if you want the audio to feedback directly
            //input.connect(audio_context.destination);
            //__log('Input connected to audio context destination.');
            recorder = new Recorder(input);
            __log('Recorder initialised.');
        }

function startRecording(button) {

            recorder && recorder.clear();
            recorder && recorder.record();
            button.disabled = true;
            button.nextElementSibling.disabled = false;
            __log('Recording...');
        }

function stopRecording(button) {

            recorder && recorder.stop();
            button.disabled = true;
            button.previousElementSibling.disabled = false;
            __log('Stopped recording.');
            // create WAV download link using audio data blob
            createDownloadLink();
            recorder.clear();
            recorder && recorder.clear();

        }

function createDownloadLink() {

            recorder && recorder.exportWAV(function(blob) {
    }
}

 window.onload = function init() {

            try {

                request = new XMLHttpRequest();
                request.mozSystem = true;

                // webkit shim
                window.AudioContext = window.AudioContext || window.webkitAudioContext;
                navigator.getUserMedia = navigator.getUserMedia || navigator.webkitGetUserMedia|| navigator.mozGetUserMedia;
                window.URL = window.URL || window.webkitURL;
                audio_context = new AudioContext;
                __log('Audio context set up.');
                __log('navigator.getUserMedia ' + (navigator.getUserMedia ? 'available.' : 'not present!'));
            } catch (e) {
                alert('No web audio support in this browser!');
            }
            navigator.getUserMedia({
                audio: true
            }, startUserMedia, function(e) {
                __log('No live audio input: ' + e);
            });
        };