So I studied the SWF 8 iPlayer a little - there are some simple rendering issues with Gnash that I'd like to come back to, but the biggest problem is obviously the media not playing. Looking at the network requests, wireshark says something about malformed packets - Gnash is getting as far as making RTMP requests, but the connection dies pretty quickly.
My working theory is that there is a bug in the Gnash RTMP client code. This code was forked from rtmpdump, and has since been converted from C to C++, and a whole bunch of other stuff. It's quite possible that there is some change deep in the code which hasn't been copied back into Gnash - therefore, it makes sense to get Gnash building against librtmp properly, which is now a separate library.
This, of course, means actually writing code. Eurgh. I try to avoid that when I can, but sometimes it is inevitable. :)
When writing larger changes, I find it takes me longer to get acquainted with the existing code base - in this case, two code bases, since I have to understand librtmp at some level, as well. I'm not expecting to produce anything before the weekend, which is frustrating. It is also risky to write about stuff before you have completed it, because it can be a very public failure if you don't manage it!