I recently bought the Samsung YP-S3 MP3 player. It's a great little gadget, but I ran into some problems converting videos (AVI & MPG) into a format that can be played on the device. The bundled software that Samsung provided wasn't able to do the conversion properly, even though it claimed to. The Internet didn't immediately yield the solutions I was hoping for either. From what I read, the SVI format Samsung uses is just MP4, with some restrictions. But any configurations I tried had no effect, and all I got was a message saying that the videos were not in the correct format.
Finally I discovered a forum post where someone suggested a tool called Any Video Converter. There is a "lite" version that is free, and so I downloaded it and tried it. I converted my AVIs to MP4, and then ran them through the Samsung software. Voila! It worked. You can even customize individual settings, like resolution, FPS, sound quality, etc. And I suspect this method can be used for some of Samsung's other players as well.
Free Download: Any Video Converter
Input formats: AVI, MPG, MOV, FLV, and loads of others
Output formats: MPG, AVI, MP4, FLV, WMV