I see that the free 'n' easy apps are covered, so I'd like to offer up something for the more technical person who wants to have lots of settings "just so" when they transcode.
For ringtones and other audio, I use
Audacity. It's FOSS and I find it very easy to use for getting sound clips out of longer recordings. For example, getting a good Homer Simpson "D'OH!" for computer events or the Underpants Gnomes song for a ringtone.
Most of my video comes from my TiVo DVRs in the proprietary encrypted TiVo file format. Although there are several free apps that use the DirectShow interface to get at the decrypted streams, I've found that
VideoReDo makes a nice, inexpensive product that can be used to do everything from cleaning up MPEG stream errors, to editing the video, to mastering and burning onto disc, or saving in a variety of file formats. The thing that really makes this product shine is that it allows me to adjust more parameters (by far!) than any other editing or transcoding product, free or pay-for. The only thing it lacks is the capability to accelerate transcoding by using GPU engines.
For fast, CUDA-based transcoding, I use Movavi Video Suite. It's OK, but definitely falls short of being a professional grade tool. Fortunately its price reflects that.
arty:
