The DSP code was written for Mozilla Fennec to use, and the only platform using Fennec is the Nokia N900. Has Nokia shipped the decoder yet?

I just found that libavcodec implementation today — It looks leagues better than the Xiph implementation, but none of the FOSStard projects I've seen use it — most link directly with liboggplay, or if they're transcoders use ffmpeg to decode the input to feed to libtheora.

That's just the thing: I can't find a source to the contrary. On2 never bragged about licensing VP3 to a customer, just distribution of the decoder through Apple and Real's auto-download mechanisms, and one in-house hosting/consulting deal with TheStreet.com in 2000.

The DSP port is an API compatible port of libtheora. Anything that is linked against libtheora can make use of the DSP port simply by linking against it. Nokia haven't shipped a major OS release since the DSP port came out, so even if they were going to ship it and/or Fennec (I have no idea), they haven't had a chance to do so yet. It's probably worth pointing out that the DSP port is not specific to the N900 or Maemo at all. It targets the C64x+ DSP, which is part of the OMAP3 SoC. The N900, Motorola Droid, and Palm Pre all ship an OMAP3 that includes the DSP.

FFmpeg has an independent decoder but for encoding it uses libtheora. The FFmpeg decoder has traditionally been slower than libtheora and didn't implement all of the Theora spec. It implemented VP3 plus the part of the spec that the Theora 1.0 (and earlier) encoders produced, but failed to decode spec-compatible output from the Theora 1.1 encoder (which libtheora 1.0's decoder handles just fine). There has been a lot of development of the FFmpeg decoder recently, so most of these issues are fixed. It's possible that the decoder is faster than libtheora now (as of the last 2-3 months), but I haven't benchmarked it.