The Zipit is a fairly capable audio device. There are several applications that can play audio on the Zipit. Yahoo! group. has some of these in the files section (see OpenZipIt / Applications / Freebase for example)
Thanks to Ken McGuire, The ZipIt's audio hardware is supported and you have access to a standard OSS-style audio device. This means that any application that works with /dev/dsp should work once compiled for the ZipIt. The Device names are a little different than what you may be used to by default. They are:
Mixer: /dev/zipm # mknod /dev/zipm c 245 0 Audio: /dev/zipaudio # mknod /dev/zipaudio c 245 4 DSP: /dev/zipd # mknod /dev/zipd c 245 3
The zipaudio device is the one you wind up dealing with most often. As on any other linux machine you can cat wav files to it and hear sound, provided the wav files are encoded to exactly what the zipaudio device is expecting.
Generally speaking, the zipaudio device expects audio data in RAW format at 44100 Hz, 2 channel, 16bits (signed little-endian) per sample. This equates to the following SOX output options:
sox inputfile.wav -t raw -c 2 -r 44100 -w -s output.wav
Note: If your audio file was created on a big-endian machine (powerpc, etc) you need to swap the bytes using the -x flag to sox
The big limitation on audio capability on the ZipIt is CPU power. The ZipIt's 90Mhz Arm CPU does not give you a lot of room for audio processing. Though some users have had success with audio decoding on the ZipIt, at 'average' bitrates, decoding the audio and playing it back seems to take the majority of the CPU.
Other applications running while performing MP3 or OGG decoding tend to make the audio 'skip' from time to time - though a well optimized / buffered player can minimize or even alleviate this.
The company that makes and markets the ZipIt, ZipitWireless has recently released an update that allows users to listen to music from their PC. Though little is known about how this is actually accomplished, it is believed that the decoding occurs on the PC, and raw audio is streamed to the ZipIt.
Similar functionality has been developed on OpenZipIt by Jay Kuri allowing users to stream any audio from their Linux desktop to their ZipIt. (note: add link to setup instructions)