Question

我在谷歌驱动器中有一个MP3文件。有没有办法可以使用谷歌应用程序脚本获得该MP3文件的duraton？

Answer 1

This页面显示了如何通过查看字节值从mp3文件中提取该信息。所以我写了一个简短的例子并测试了它。它似乎与我到目前为止尝试的所有mp3文件一起正常工作，但不能保证它将始终有效。 getPlayTime函数以秒为单位返回播放时间。

function getPlayTime(file) {
  var bitratesV1 = [0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320],
      bitratesV2 = [0,  8, 16, 24, 32, 40, 48, 56,  64,  80,  96, 112, 128, 144, 160];
  var bytes = file.getBlob().getBytes();
  for(var pos = 0;pos < bytes.length; pos++) {
    if(bytes[pos] === -1 && pos < bytes.length - 3 && (bytes[pos+1]&0xF0) === 0xF0) {
      var isMpegVersion2 = (bytes[pos+1]&8) !== 8,
          isLayer3 = (bytes[pos+1]&6) === 2,
          bitRate = ((bytes[pos+2]&0xF0) >>> 4)&0xF;
      if(!isLayer3) continue;
      if(isMpegVersion2) bitRate = bitratesV2[bitRate];
      else bitRate = bitratesV1[bitRate];
      var playTime = bytes.length*8/(1000 * bitRate);
      return playTime;
    }
  }
}

function test() {
  var file = DriveApp.getFilesByName("music.mp3").next();
  var playTime = getPlayTime(file);
  Logger.log(playTime);
}

编辑：这是一个希望更准确但也更慢的版本

function getRunTime(file) {
  var playTime = 0, numFrames = 0;
  var bitratesV1 = [0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320],
      bitratesV2 = [0,  8, 16, 24, 32, 40, 48, 56,  64,  80,  96, 112, 128, 144, 160];
  var bytes = file.getBlob().getBytes();
  for(var pos = 0;pos < bytes.length; pos++) {
    if(bytes[pos] === -1 && pos < bytes.length - 3 && (bytes[pos+1]&0xF0) === 0xF0) {
      var isMpegVersion2 = (bytes[pos+1]&8) !== 8,
          isLayer3 = (bytes[pos+1]&6) === 2,
          bitRate = ((bytes[pos+2]&0xF0) >>> 4)&0xF;
      if(!isLayer3) continue;
      if(isMpegVersion2) bitRate = bitratesV2[bitRate];
      else bitRate = bitratesV1[bitRate];
      var pt = bytes.length*8/(1000 * bitRate);
      if(!isNaN(pt) && isFinite(pt)) {
        playTime += pt;
        numFrames++;
      }
    }
  }
  return playTime/numFrames;
}

从App脚本中读取M3文件的持续时间

1 个答案: