It turned out to be at least partly a problem with my proxy code. The ice-cast stream doesn't include a Content-Length header (because you know, it's a stream), so this was causing libfxplugins to crash as in my previous post on the subject. Shouldn't really cause a crash - at most it should just throw a protocol error exception? Not sure if it has javafx security implications (e.g. if media on a web page through the web component goes through the same mechanism it certainly does - Update: I filed a bug in jira, and it seems to have been escalated - even at this late stage of java 8).
If I add a made-up content-length value at least I get the music playing, .. but the 'user experience' isn't very good because it seems to change how much it pre-buffers depending on the reported length (rather strange i think). So if i report 1-10M it starts after a few seconds but if i report some gigantic number it buffers for minutes (or maybe it never starts, i lost patience). The problem is that as the data length is hounoured (as it should be) which means that too small a number causes the stream to finish quickly. And it seems to read the same stream twice at the same time which is also odd.
To be blunt I find it pretty perplexing 'in this day and age' that javafx doesn't support streaming media to start with. Or that g-"so-called-streamer" seems to be the reason for this. If I could work out how to compile libfxplugins.so from the openjfx dist I would have a poke, but alas ...
I was going to go ahead with the application anyway but I think because of this streaming issue I wont - or if I do I wont be using javafx to do the decoding which is a bit of a pain.
Update 2: The bug has just been patched. 4 working days from reporting and if the openjdk schedule is still correct, just 2 weeks from release. So yeah I guess it was reasonably important and even just mucking about has value.