Flash supports both downloading and progressive loading of audio. Progressive loading means that the audio plays as it loads, which is like streaming except that the file accumulates in user's RAM and is eventually moved onto the hard drive for subsequent use.

Unlike true streaming, the advantage of progressive download is that the file plays from hard drive and does not need to re-stream for subsequent playback. A disadvantage, also unlike streaming, is that Flash does not handle large files well because they can use too much RAM. Another disadvantage is that the after playback there is a copy of the file on the user's computer. This is not the case with true streaming.

All vesions of flash progressively load sounds in SWF set to stream sync.

Flash 6+ can either progressively load or download native mp3. You do not need to create sound only SWF for audio streaming in Flash 6+.

Make sure you require Flash 6r40 or greater to avoid mp3 streaming bugs. Earlier versions did not support the sound object start method and also did not terminate download unless you actually quit the browser, causing bandwidth clog.

Also Flash cannot play just any old MP3, the sample rates must be 44,22,11, the bitrate must be one of the supported rates listed in the Sound Properties window and the file must be encded with CBR not VBR.