Recipe 15.3. Setting the Buffer for a Sound

Problem

You want to ensure that a streaming sound plays smoothly.

Solution

Set a buffer time by using the SoundLoaderContext class.

Discussion

The Sound class streams audio as it plays, which means that a sound starts playing before it is fully downloaded. This is especially useful for larger sound files, such as full songs, which can be several megabytes in size.

Depending on how your sound is encoded and the available bandwidth, a sound may be playing faster than it is downloading. In this case, the sound may pause while it waits for more sound data to load in. To safeguard against this, you can set a buffer. This causes the Sound object to pre-load a certain amount of sound data before it starts playing. Then, if there is a momentary slowdown in bandwidth, the sound can keep playing the buffered data without pausing.

By default, a Sound object creates a one-second buffer when you tell it to load a sound file. In other words, even if you tell it to play immediately, the Sound object waits until at least one second's worth of sound data has come in. Additionally, if that buffer is used up and the sound needs to stop to wait for more data, it refills that one-second buffer before it resumes playing again.

If you are unsure of network conditions or have sound files that were encoded at a high bitrate (requiring more bits of information per second of playing time), then you may want to increase the size of this buffer to ensure smoother playback. You do this by creating a SoundLoaderContext object, passing in the size of the buffer, in milliseconds, to the constructor. For example, if you wanted to create a five-second buffer, you would do the following:

buffer = new SoundLoaderContext(5000);

You can use this object for either method of loading a soundin the constructor of the Sound object, or in the load( ) method (see Recipe 15.1). Just pass it in as the second parameter after the URLRequest parameter, as shown here:

var request:URLRequest = new URLRequest("song.mp3"); var buffer:SoundLoaderContext = new SoundLoaderContext(5000); _sound = new Sound(request, buffer); _sound.play(  );

or:

var request:URLRequest = new URLRequest("song.mp3"); var buffer:SoundLoaderContext = new SoundLoaderContext(5000); _sound = new Sound(  ); _sound.load(request, buffer); _sound.play(  );

Problem

Solution

Discussion

See Also