NVIDIA regarded the FX5500 as an entry level GPU and was capable of playing basic HD video under windows (DirectX 9). Direct support under Ubuntu is no longer available from NVIDIA - only through their legacy 173 driver.

You will struggle to play HD videos under Ubuntu - the fundamental issue is the lack of VDPAU support for your graphics card in the NVIDIA driver. VDPAU support is the ability for Ubuntu to offload graphics processing to the graphics card itself - without it your PC is doing much of this work. It would be useful to add the specs of your PC into your question.

Tips

1. Check if you have vsync support (Sync to VBlank) in your nvidia-settings (opengl/xvideo)- Turning this on can help.


2. If you are feeling brave - look at overclocking your FX5500 to maximise the framerate possible - search for "nvclock" in Software Center. I've managed to overclock my Geforce 6 by an extra 10% which improves framerate slightly.


3. Compiz - this can slow down framerates - look at viewing your video under "Ubuntu Classic (No Effects)" if you are using Natty. If lucid of maverick - look at using Compiz Fusion to do something similar. Compiz, whilst not significant, if you are looking for the extra 2-5% performance boost could perhaps make a just that little bit of a difference to a slight lag issue.


4. You may have more luck with updated X-system. Have a backup first just in-case you get blackscreens on boot - and the look to test with the X-Swat PPA.


5. CPU overclock - I have a bios that allows my Athlon XP based CPU increase from 1.1GHz to 1.9Ghz - obviously this makes a significant difference in overall system performance - and does improve graphics decoding and encoding abilities.