Preloading MP3 and FLV files

To preload MP3 and FLV files, you can use the setInterval() function to create a "polling" mechanism that checks the bytes loaded for a Sound or NetStream object at predetermined intervals. To track the download progress of MP3 files, use the Sound.getBytesLoaded() and Sound.getBytesTotal() methods; to track the download progress of FLV files, use the NetStream.bytesLoaded and NetStream.bytesTotal properties.

The following code uses setInterval() to check the bytes loaded for a Sound or NetStream object at predetermined intervals.

// Create a new Sound object to play the sound.
var songTrack = new Sound();
// Create the polling function that tracks download progress.
// This is the function that is "polled." It checks 
// the download progress of the Sound object passed as a reference.
checkProgress = function (soundObj) {
  var bytesLoaded = soundObj.getBytesLoaded();
  var bytesTotal = soundObj.getBytesTotal();
  var percentLoaded = Math.floor(bytesLoaded/bytesTotal * 100);
  trace("%" + percentLoaded + " loaded.");
}
// When the file has finished loading, clear the interval polling.
songTrack.onLoad = function () {
  clearInterval(poll);
}
// Load streaming MP3 file and start calling checkProgress()
songTrack.loadSound("beethoven.mp3", true);
var poll = setInterval(checkProgress, 1000, songTrack);

You can use this same kind of polling technique to preload external FLV files. To get the total bytes and current number of bytes loaded for an FLV file, use the NetStream.bytesLoaded and NetStream.bytesTotal properties.

Another way to preload FLV files is to use the NetStream.setBufferTime() method. This method takes a single parameter that indicates the number of seconds of the FLV stream to download before playback begins.

For more information, see MovieClip.getBytesLoaded(), MovieClip.getBytesTotal(), NetStream.bytesLoaded, NetStream.bytesTotal, NetStream.setBufferTime(), setInterval(), Sound.getBytesLoaded(), and Sound.getBytesTotal().