Sound Synchronization

Java Sound & OpenAL
#1

I’m trying to get sound and graphic synchronization when playing music using a SourceDataLine - the Java code is a sound editor I wrote over 2 years ago and I’m updating it to be more useful since I failed to work this out 2 years ago and I’m now trying to get it to work
Although this isn’t a game, no doubt in a game you would want to be able to sychronize graphic events during a sound being played - so hopefully someone here knows the answer …
I have graphic views of each wave being played and want to run a bar across the graphics as it is playing
Other than synchronization, everything works fine.
The bar is drawn by a separate thread that loops doing: delete the old bar, get the position of the new bar, draw the new bar then sleep 100ms
I’ve tried:

  1. line.getFramePosition() or line.getMicrosecondPosition() but they appear to NOT be based on audio output, rather they seem to be the value of data written to the line
  2. process a full buffer first, call line.start() then get System.currentTimeMillis() then write each buffer - in the loop use currentTimeMillis() to get the current time offset from start of audio ouput - this produces two results - sometimes it’s very close to sync and other times it’s out (audio behind sync) by the same amount
  3. use a LineListener to catch START and get System.currentTimeMillis() as the time that audio output started - but in the START LineEvent the current frame is either around 500 (audio is behind by about 250ms) or around 4000 (sync almost correct) but for 44.1kHz - 250ms is approx 11000 frames so there is no obvious way to fix the time based on the frame position

As I said in 2) and 3) - the graphics is AHEAD of the audio - not lagging behind due to execution speed. I need to work out another way to do it properly or else work out how to calculate the sync offset in 2) or 3)

The audio is OK - no skips or jumps or drop outs (except on very rare occasions - and they are so rare that I don’t care about them)

I run the sound editor on 2 different machines:

  1. Athlon 1600+ 512MB using RedHat Linux 9 Java 1.4.2-b28
  2. PIII500 384MB WinXP Home Java 1.4.1_02

On the PIII500: sync is worse in all cases

#2

I’m not sure if this helps, but at least you could try to use the high resolution timer in J2SE 1.4.2 instead of the inaccurate currentTimeMillis. You can read more about the high resolution timer here:
http://www.java-gaming.org/cgi-bin/JGNetForums/YaBB.cgi?board=Tuning;action=display;num=1053157119

#3

OK, the bad new is … it’s the Linux Java implementation that’s the problem :frowning:
I only tested it a few times on Windows and I must have done that with hacks that I was trying to get to work but were wrong
Coz now when using line.getMicrosecondPosition() it does seem to be correct on Windows but not on Linux
I’m not 100% certain that it is exact on Windows but it does appear to be close enough that it could be OK
Also, I found that Juke.java in the JavaSound demo also displays a counter that is wrong on Linux but appears to be OK on Windows
Oh well, off to the sun bug parade …

#4

Could you elaborate on that? I too am interested in this subject but am (very) new to audio programming.

Why can’t you read the frame in the event and adjust the time returned from your timer based on the frame’s value? Can’t you use this value to determine when to start the graphics, and if they’ve already started how much to adjust them by?