I implemented the captioning plug-in in the same fashion as the CaptioningSample found in the OSMF source download. It works fine with progressive videos but when I set the URLResource to a dynamic stream it doesn't show. Is it possible to do captioning with dynamic streaming videos?
Yes, it should work fine. I modified the CaptioningSample to use the DefaultMediaFactory, loaded the SMILPlugin, and called mediaFactory.createMediaElement() passing in an RTMP MBR SMIL file and it works fine. Of course the captions don't match the video but they show up at the correct time as specified by DFXP file in the sample.