Check out some VSO products...I think the Video Converter is the one you want though.  I've used convertxtodvd from them for the past 3-4 years and and is simply the best compared to others.
 
Link:  http://www.vso-software.fr/products/video-converter/vso-video-converter.php

If you are interested in a high quality encoding then you do not want to use a CUDA encoder.  I would stick to handbrake and tweak the settings to make it faster.  CUDA encoder can be faster, but at the expense of quality.  You can speed up a CPU encode a lot too at the expense of some quality.
 
Just understand a CUDA or QuickSync encoder is not faster than a CPU for video encoding when you adjust the encoders for the same output quality.  It's just useful if you don't want your CPU completely utilized during the long encoding process.
 
And the problem with CUDA and Quicksync encoders is you can't adjust them to high quality other than using a really high bitrate which will produce a large file.  With a CPU encoder like x264 you can adjust very fine settings to get a high quality output in a very small file, it just takes a long time to encode.

Hi, For several months I am using Program4Pc Video Converter Pro and it works very good, every month the new update version comes out (free of charge) with supporting more devices, now they support more than 300 formats and portable devices.
Check its trial version at official website:

 
 
 

As far as i know, i highly recommend iDealshare VideoGo which supports CUDA very successfully and great.
You may free download the to have a free try at
It supports convert among almost all kinds of video and audio files like AVCHD, MXF, TS, MTS, M2T, M2TS, SWF, AVI, MPEG, WMV, DivX, MP4, H.264/AVC, MKV, RM, MOV, XviD, 3GP, WTV, FLV, MP3, WAV, WMA, M4A, 3GA, Apple Lossless ALAC, CAF, FLAC, OGG, M4B, MKA, AAC, AC3, DTS, RA, RAM, APE, AU, AUD, AIFF, AIF, AIFC, MPC, QCP, SHN, TTA, PCM, AMR, AWB, VOC, VOX, MPC etc
 

Is there a converter that supports SLI? I've tried several and they all seem to only use 1 card. I convert hundreds of movies per week, would be nice to see one that uses all four of my X's.
 
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DVDFab is a good choice.

I would recommend Freemake Video Converter

Charlesberry
I'd recommend Acethinker Video Converter which I have used for many years. It's a free web-based application to convert videos, you don't have to install anything. Support CUDA.

Sir, it seems that you know a lot about video converters, i also have a related question and want to know whether you know the solution. Yesterday, i find this article about video conversion and it recommend me to download their video converter to convert MP4 format. In the tutorial, as you can see  from ( they claim that the video size can be compressed after conversion process. However, after i converted my MP4 to AVI format, the size got bigger, around 40 percent bigger than the original one while the quality stayed the same. How strange it is. Do you know what may happen during the conversion?

Wish i could find converting software that could get rid of black bars on videos without cropping (zooming in).
 
 
 

mts video converter should have a try.   MTS Converter not only lets you convert MTS to various formats but also convert M2TS  . AVI, MP4, WMV, MOV, MPG, FLV, and RMVB, to meet high-end demands, this MTS file Converter supports to convert to 3D video format for playback with life like 3D effect.  convertmtsfiles.net