I wanted to be able to specify both an rtmp stream as well as a different url for HTML5 fallback (for the iPad/iPhone/etc). The plugin doesn't support this natively so I added as alt_file field, which, if specified, the plugin will use as the HTML5 player source. If you need to accomplish the same thing, the patch is attached. Additionally, I think the logic in generate_embed_code() when deciding if the User-Agent was an iPad was backwards, so I corrected that as well.
Finally, I think a feature like this (if not this exact implementation) would be nice for the plugin to have.