If you are looking to convert video of audio files, http://media-convert.com/ may be the place to do it, simply select the file you want to convert and choose your output format. Your browser then uploads it to the website which converts it then provides you with a download to the converted media.
Probably best for small clips given that most internet upload speeds are rediculously slow, and have to include the traffic usage. Also would probably want to stay away from files you wouldn’t want accidentally being exposed to download to the whole world either.