Recently, I had programmed a pretty solid mp3 player in AS2, Flash 8. The resulted size of the SWF is 24kb, mainly because of the embedded PNG background bitmap. I relied on External Interface to communicate with JavaScript routines and it works flawlessly for me. SWFObject was used to embed the SWF into the HTML page
It feels really nice to release the product that will be used by 1000+ of people.
The web-site language is Russian, it is social network with a focus on mobile users.
The mp3 player in particular allows to set 2 markers for the song to allow the cut of the song selection to become a ringtone at the mobile.