设置使用Recorder.js录制音频的时间限制？

Question

我能够使用recorder.js在浏览器中录制音频，但无法应用30秒的时限来停止录制。

function startRecording（）{     console.log（“ recordButton clicked”）;

/*
    Simple constraints object, for more advanced audio features see
    https://addpipe.com/blog/audio-constraints-getusermedia/
*/

var constraints = { audio: true, video:false }

/*
    Disable the record button until we get a success or fail from getUserMedia() 
*/

recordButton.disabled = true;
stopButton.disabled = false;
pauseButton.disabled = false

/*
    We're using the standard promise based getUserMedia() 
    https://developer.mozilla.org/en-US/docs/Web/API/MediaDevices/getUserMedia
*/

navigator.mediaDevices.getUserMedia(constraints).then(function(stream) {
    console.log("getUserMedia() success, stream created, initializing Recorder.js ...");

    /*
        create an audio context after getUserMedia is called
        sampleRate might change after getUserMedia is called, like it does on macOS when recording through AirPods
        the sampleRate defaults to the one set in your OS for your playback device

    */
    console.log('audio1')
    audioContext = new AudioContext();
    console.log('audio2',audioContext)
    //update the format 
    //document.getElementById("formats").innerHTML="Format: 1 channel pcm @ "+audioContext.sampleRate/1000+"kHz"
    /*  assign to gumStream for later use  */
    gumStream = stream;

    /* use the stream */
    input = audioContext.createMediaStreamSource(stream);

    /* 
        Create the Recorder object and configure to record mono sound (1 channel)
        Recording 2 channels  will double the file size
    */
    rec = new Recorder(input,{numChannels:1})

    //start the recording process
    rec.record()
    console.log('chunks',rec)
    var chunks=[];
  input.ondataavailable = function(e) {
        console.log(input);
        console.log(e.data);
        chunks.push(e.data);
      }
 console.log(chunks)
 var blob1=new Blob(chunks, { 'type' : 'audio/wav; codecs=opus' });
 console.log('***********',blob1);

    console.log("Recording started");




}).catch(function(err) {
    //enable the record button if getUserMedia() fails
    recordButton.disabled = false;
    stopButton.disabled = true;
    pauseButton.disabled = true
});

}

这是我开始录制的功能

function stopRecording（）{     console.log（“ stopButton clicked”）;

//disable the stop button, enable the record too allow for new recordings
stopButton.disabled = true;
recordButton.disabled = false;
pauseButton.disabled = true;

//reset button just in case the recording is stopped while paused
pauseButton.innerHTML="Pause";

//tell the recorder to stop the recording
rec.stop();

//stop microphone access
gumStream.getAudioTracks()[0].stop();

//create the wav blob and pass it on to createDownloadLink
rec.exportWAV(createDownloadLink);

}

这是要停止录制。

所以在startRecording 30秒后，我想打电话给StopRecording