Technical Q&A SND08

Playing Compressed WAVE files via the Sound Manager

You have to do all of the sound header parsing yourself, just as you do for an uncompressed sound, and then you have data which you may or may not be able to directly pass to the Sound Manager.

If the WAVE is formatted using µlaw then your program doesn't have to do anything special. Since the µlaw file is processed on a byte by byte, and there is no endian difference between the same data as an AIFF or WAVE file, the standard Mac µlaw decompressor can deal with this data without a problem.

On the other hand, you cannot play IMA-ADPCM compressed WAVE files as simply as you could play a µlaw WAVE files because of the difference in the actual data stream of a sound compressed with the Mac's IMA compressor versus the same sound compressed with the Windows' IMA-ADPCM compressor.

You have to deal with Windows' IMA-ADPCM compressed WAVE sounds just as you would any sound which required a custom decompressor. Your program does all the decompression. This can be done either by writing a decompression component for the Mac (in which case any program can use it), or by having a decompression function in your program.

If you write your own 'sdec' then you can use any Sound Manager routine that will play an arbitrarily compressed sound, just make sure to say that the sound header says the sound is compressed with your compressor so that the Sound Manager will call your 'sdec'.

If you choose not to write a decompression component and you can decompress the sound completely, then you can use any Sound Manager call that takes a buffer of uncompressed sound. If you can't decompress the sound completely then you will have to decompress it in chunks and use SndPlayDoubleBuffer or bufferCmd's to play each chunk.

[Sep 27 1996]