ux.ts

  //
  // ensure that recorded mp3 contains audio
  // - https://stackoverflow.com/questions/71103807/detect-silence-in-audio-recording
  async detectSound(content) {
    const MIN_DECIBELS = -45;
    const audioCtx:AudioContext = new(window.AudioContext || (<any>window).webkitAudioContext)();

    const blobUrl = (content.blob)?URL.createObjectURL(content.blob):content.url;
    const audio = new Audio();
    audio.playbackRate=2;
    audio.src = blobUrl;
    audio.volume = 0;

    const audioSource:MediaElementAudioSourceNode = audioCtx.createMediaElementSource(audio);

    // Create an analyser
    const analyser = audioCtx.createAnalyser();
    analyser.minDecibels = MIN_DECIBELS;
    audioSource.connect(analyser);
    const bufferLength = analyser.frequencyBinCount;
    const domainData = new Uint8Array(bufferLength);


    // Connect parts to get audio buffer
    analyser.connect(audioCtx.destination);
    await audio.play();

    return new Promise((resolve,reject)=> {
      const processSound = () => {
  
        analyser.getByteFrequencyData(domainData);
        for (let i = 0; i < bufferLength; i++) {
          if (domainData[i] > 0) {
            return resolve(true);
          }
        }
        window.requestAnimationFrame(processSound);
      }
      window.requestAnimationFrame(processSound);  
    });
  }