There are many desktop apps and web sites offering downloads of web videos from sites like Youtube, Google Video, Dailymotion etc. There are few services that offer on the fly conversion of these videos to other formats so you can play them on different devices.
Filsh.net is a service that allows you to covert web videos to other formats before downloading to your PC. Enter the URL of the video you want to convert and download, select the format for your conversion and then click the yellow button. It will start converting the video, the quality of the conversion is not bad, but youtube video quality has never been that great. When you select the format of the conversion it offers you to change the encoding parameters like audio bitrate, video bitrate.
The supported conversion formats include AVI, MPG, WMV, WMA, AAC, MOV, MP4, DPG, 3GP, OGG or MP3 and Flash.
You could also convert your desktop videos by uploading to the site. It has a simple to use interface, the site is in German but you can easily make out what you have to do to convert a youtube video. The conversion is quick, of course it depends on the format you selected for the conversion. Vixy.net is a similar service for converting web videos. Via Download Squad