Even a zipped version of the raw WAV files is still twice the size of the IMA4 compressed data. For example, a 100KB WAV file compresses to ~64KB when zipped, but ~32KB via IMA4.

IMA4 is a compression format designed specifically for audio, so it is able to compress it really well by making assumptions about how most audio data looks. It’s basically able to compress 16-bit frames down to 4-bit nibbles. It tacks a 2-byte header onto each packet, which is why it’s not *quite* 4:1 in the end. But it’s still an impressive compression ratio.

Interesting approach to the IMA4 code. My first impression when I was reading your blog is why not use zip or other built-in compression that ships with your app and then have the files uncompressed in an initialization phase the first time the app is run? I guess you lose the compressed file’s space, but that’s about it. I’m lazy I guess…. =)

I’d be interested in seeing the code you’ve got going regardless, sounds like an interesting project.