Swing Hacks

Play Non-Trivial Audio #76

Chapter 10, Audio

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387

HACK

Grabbing a DataLine

This hack is going to play an uncompressed (i.e., PCM) AIFF or WAV file of

arbitrary length by getting a

DataLine for the data and then repeatedly read-

ing the data from disk and writing it to the

DataLine

.

PCM stands for Pulse Code Modulation, which means that

analog audio has been sampled at regular intervals and quan-

tized (i.e., each sample is expressed as a numeric value). It’s

the lowest-level, most common denominator data that Java-

Sound understands, since it can be delivered directly to a

sound system for playback.

The class to do this will be called PCMFilePlayer. Given a file, its responsibil-

ities are to:

1. Verify that the file contains PCM data (signed or unsigned).

2. Get a

Line for this format.

3. Kick off a thread to read bytes from the file and write them to the

Line,

which plays them.

Reading and writing bytes doesn’t sound too bad, but JavaSound imposes

another requirement on you: you have to send complete frames, not just a

bunch of bytes, to the

Line. A frame is one complete sample of audio in

whatever format you’re dealing with. For the PCM formats supported by

this hack, a frame can be one of three sizes:

• 1 byte for 8-bit mono sound

• 2 bytes for either 8-bit stereo sound or 16-bit mono sound

• 4 bytes for 16-bit stereo sound

The implication for the read-write loop is that if you read some number of

bytes