Swing Hacks

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Chapter 10, Audio

#77 Show Audio Information While Playing Sound

HACK

Running the Hacked Hack

When you run this hack, you finally get a player with a level meter, as seen

in Figure 10-9.

While this looks OK in a book, it really isn’t very satisfactory when you’re

watching the audio as it plays. It doesn’t seem to relate to the music that

closely; that is, it seems to follow softer music OK, but it really falls apart on

rock music.

Part of the reason is that this “maximum” algorithm is quite crude; an

approach such as averaging the samples in the buffer might be more realistic.

But the real problem is that the access JavaSound gives you is doomed to be

hopelessly behind what’s being played. Think about the

available( )

method, which reports how much you can write to the SourceDataLine’s

buffer without blocking. What’s happening is that you’re refilling one end of

its buffer, while it drains out the other end to the speakers—or more accu-

rately, to the native sound system (which may have its own buffers, and thus

more latency). This arrangement is illustrated in Figure 10-10.

So, you can calculate the level for the samples in the buffer, but it will be

some time until those samples are played, so you have a mismatch of what’s

being measured and what’s actually being played. What you need is access

to the

SourceDataLine’s buffer, so you could run the level check on the bytes

that are just about to be played. Until and unless that’s available, the sug-

gested workaround isn’t really going to work.

Figure 10-9. Audio player display with format information and level meter

Figure 10-10. Flow of samples through buffers in JavaSound

read()

Your buffer

write()

Available To native soundPreviously written data

SourceDataLine’s buffer