StaxRip is a powerful tool for converting videos to MP4, which offers far more options and control than most of the competition.
The program can import a lengthy list of source video formats, for instance: 264, AVC, AVI, AVS, D2V, DGA, DGI, DIVX, FLV, H264, M2V, M2T, M2TS, MKV, MP4, MPEG, MPV, MOV, OGM, OGG, PVA, RMVB, TS, VOB, WEBM and WMV.
And these can then be converted to general MP4 files, MP4's optimised for the iPod/ iPhone, and a few other formats: MKV, AVI, WebM and so on.
The conversion process itself is carried out by a host of free and open source tools which come bundled with the program: AviSynth, FFmpeg, MKVtoolnix, VirtualDubMod and many more. (Don't worry, there's no massive installer, you just unzip them and go.)
And StaxRip itself acts as a front end, allowing you to configure precisely how its various components work.
You don't have to get involved in its more complex depths. Choose an input file, an output format and the program will use reasonable defaults for everything else.
But if you need more power, then you're also able to apply filters, set your pixel aspect ratio, decide which encoder you'd like to use for a particular task, pick the most appropriate audio and video codec, then configure all of them in extreme detail. (If you care about XviD's quantization settings, for example, then good news: you can set them all here.)
Video conversion novices will quickly become confused by all the options and jargon flying around here, then. But if you find other transcoding tools to be a little basic, then StaxRip's extreme configurability means it's definitely worth a few minutes of your time.