JavaScript 計算音頻時長

1. 使用Audio獲取duration

  let audioUrl;
  let duration = 0;
  const processDuration = (blob: Blob) => {
    const reader = new FileReader();
    reader.onloadend = e => {
      audioUrl = reader.result as string;
      var media = new Audio(reader.result as string);
      media.onloadedmetadata = function() {
        if (media.duration != Infinity) {
          duration = media.duration;
        }
      };
    };
    reader.readAsDataURL(blob);
  };

但這個方法在Chrome上會存在bug，可能會計算duration為Infinity。可以嘗試用下面方法解決。

2. 直接獲取audiobuffer的duration

audioBuffer.duration

3. 用arraybuffer計算duration

如果獲取的是純pcm數據的arraybuffer，且知道audio的samplerate，計算$$duration = arraybuffer.bytelength / sampleRate / 2$$