http://www.videohelp.com/software/As-Video-Converter
Whenever there is a video app on GOTD, odds are someone will ask &/or comment on hardware GPU acceleration. GPU assist for video has been around for years, since HD video really, with further development driven by [especially lower powered] CPU/GPU combo chips. AMD, Intel, & Nvidia all have their proprietary tech for accelerating video processing -- AMD & Intel also support OpenCL while Nvidia backed away from it. However Nvidia *may* be returning to OpenCL. As the name suggests, Open CL is an open programming framework that can be used for all sorts of GPU hardware assist -- not just video. [GPUs are great at certain types of number crunching, from Wall St. to criminals cracking passwords.]
Generally higher end video & image editing apps use OpenCL, while less expensive & free software tends to use those proprietary methods of GPU acceleration. Nvidia's CUDA used to be the best known & most popular, but, according to medialooks.com: "Since version 340.52 of Nvidia's drivers CUDA is disabled and replaced with NVENC".
Cyberlink's Expresso -- now MediaExpresso -- was one of the 1st, if not The 1st video converter/encoder to use the maximum amount of that proprietary GPU acceleration. A's Video Converter was/is the free alternative, focusing originally on AMD [then ATI], & now with Intel GPU support. [I think for a while it also supported CUDA but I may be wrong.]
Maxing out GPU assist means conversion [encoding] can be extremely fast -- in some cases I've seen over 800 fps myself, though that will vary depending on the input & output formats & frame sizes. The downside is that quality will suffer -- think of it this way: GPU assist uses shortcut routines coded into the hardware that don't always exactly match what you'd use to get the absolute best quality using only the CPU.
That doesn't necessarily mean that the results will look nasty -- when you encode using only the CPU, software encoder settings determine quality, with the best quality being terribly slow [as in overnight or even a day or two], while the fastest settings may not give you quality that's much better [IF it's any better] than Expresso or A's. BUT, this is also dependent on the encoder used, & how it compares to alternatives with your target format & frame size.
I'll use H.264/AVC as an example... The open source x264 is a world class encoder, but it includes very few options or operations that can use GPU assist. Encoding apps that focus on GPU assist then use something else, code based on the software SDK [Software Development Kit] developed by the manufacturers to work with their GPUs. In some cases that's good enough, but not always -- you'd have to run a short test both ways & decide.
Higher end software like Sony's Vegas Pro try to split the work between the CPU & GPU, using the GPU for the operations it does best with highest quality, & the CPU for everything else. How well that works depends on your input & output formats & frame sizes along with your hardware & software you've installed. Considering the asking price, unless you need the rest of the NLE capabilities, you're better off putting up with the speeds you get from the average ffmpeg converter, or trying MediaExpresso or A's.
http://www.cyberlink.com/products/mediaespresso/features_en_US.html
http://www.anandtech.com/show/9139/nvidia-posts-35005-hotfix-driver-fixes-games-adds-opencl-12-support
http://blog.medialooks.com/814EAo/