Before going on I do not rate any of the "one click"/"simple" apps that can use GPU stuff (I do not care for one click apps in general), if you want to go down this road then you really need to be able to handle yourself in video encoding circles.
Also before this starts some people walk into this expecting orders of magnitude increases and are disappointed (many of the numbers are not outright lies but shall we say the people making them are comfortable with statistics, know how to test things and not to test things and I shall certainly not rule out dishonesty). While the cards can act as a poor mans hardware encoder I would sooner get one of them.
There are several types of GPU accelerated video apps but for the most part it is still in a largely experimental/initial implementation stage as coding for it is a nightmare.
I will detail good ones but be sure to read up on the encoder when you get it as a lot of them implement a tiny fraction of the spec compared to other more traditional encoders have and there is little point of encoding a bad quality video slightly more quickly or just plain do it badly (again damn hard to code for).
For you though Nvidia can use CUDA (others reading if you have an earlier 8XXX series some apps may now be able to use it) which is probably best way (compared to things like implementing sections in various APIs not designed for encoding).
The fact I mention this though should indicate you are going to have to work through a minefield of different APIs (openCL, brookGPU, directX, CUDA, driver level, abusing graphics rendering APIs and the list can go on). Not all methods are created equal by any stretch (far more so than any of the other API "wars" that have ever gone on) but the selection of devices that can use it also changes. You also have to remember that GPUs are not all that fast to begin with and the 8XXX and beyond are at the risk of starting a flame fest just 7XXX or worse with directX10 and a decoder chip glued on when it comes down to it.
First I will mention decoders like
http://neuron2.net/dgmpgdecnv/dgmpgdecnv.html , personally I find these more up my street. If you have not seen the dgmpgdec and dgavcdec they are great tools for parsing MPEG (MPEG2 is DVD as is a lot of digital TV and it is what most people use the app for as it supports both very well) and AVC (aka h264 aka MPEG4 part 10 although that one lacks serious container support although it is not like demuxing is hard) to use in later encoders (mainly avisynth based).
The basic packages use the CPU but the NV versions (which you need to cough up $15 for) use the GPU.
Kicking decoding to the GPU leaves you with more CPU to play with and multicore encoding is coming along very nicely if only in the somewhat kludge like form of split the video in pieces method. More cores/threads does open up issues with cache and disc speed though which I suggest you also look at.
You also have more basic things like
http://mythtv.org/pipermail/mythtv-dev/200...ber/063677.html (I know this is for unix but it gives a good idea) and
http://www.nvidia.co.uk/page/purevideo.html or even
http://www.coreavc.com/
I have also seen a few filters making use of the GPU ranging from noise reduction (
http://compression.ru/video/denoising/index_en.html and
http://forum.doom9.org/showthread.php?t=89941 ) to resizing to deinterlacing to inpainting right back to colorspace conversion with these far more suited to massively parallel systems than straight up encoding is. Again watch for the varying APIs and most of this sort of thing is limited to avisynth and high end virtual dub filters.
That over onto encoders, there are presently around 5 of them with a couple already mentioned.
First up is
http://www.elementaltechnologies.com/produ...erator/purchase
About $2k for a basic encoder that is up to quality with software encoders (x264) and will need some more hardware (the software comes with the hardware)
Nero move it:
http://www.nero.com/enu/moveit-nvidia-cuda.html
Much cheaper, see my arguments on incomplete specs above.
http://www.coreimg.com/English/index.php
Never heard of it before 5 minutes ago and as such I will spare it discussion.
I will also spare you in depth discussion on the theory behind it all, a search for GPU encoding at
http://forum.doom9.org/ will do far better for that sort of thing with
http://forum.doom9.org/showthread.php?t=142797 being a good start.
Frankly use it for decoding or those handful of filters, leave encoding for the CPU at least for the next year or two.
