Your browser would need to be configurable to run video through a player
that supports the DSP. Not sure about the angstrom and Ubuntu builds
but I think a gstreamer-based solution may work with those, if you can
get your browser to call it. I'm not sure which other players have DSP
support, but I'd guess if any do it would be mplayer. Maybe that
requires ffmpeg DSP support. Dunno for sure.
Gstreamer/mplayer/other video player needs DSP support to perform
hardware accelerated video decoding. You can use the processor for this
(without DSP) to playback standard definition quality video. HD may
need DSP support to get what you're after. Try playing a video you
created for your system without DSP and see if it plays at the rate you
require. If not, you may need to get DSP working.
SGX is OpenGL, which you need if you want to play 3D games or
hardware-accelerated Flash video. Note that Adobe has a Flash player
for ARM but I don't know (yet) how easy it is to get. You'd also need
OpenGL for media platforms like XBMC. Technically you don't need SGX to
playback video, depending on the kind of video.
Running OpenGL under X.org requires using the SGX provided 1.9.4
X-Server and supporting components. That's so you can access the binary
blobs that provide the 3D acceleration for the PowerVR hardware
graphics. There is a small tradeoff here for performance. The PowerVR
binaries are softfp, not hardfp. So you're toolchain will need to be
softfp too. Hardfp would be better, but without source you can't
recompile the binary blobs. Robert Nelson has some special releases of
SGX that has hardfp to address that problem when using his Ubuntu
Bridgedriver is for DSP. tidspbridge is, I believe, a variation on
that. I'm using bridgedriver with gst-dsp to try and get video decoding
supported in my project (it's not 100% working yet).
Hope that helps a little.