Documentation:Media Conversion Tools
- CloudConvert https://cloudconvert.org/ more than 100 different audio, video, document, ebook, archive, image, spreadsheet and presentation formats.
- Online Converter http://www.online-convert.com/ provides free conversion between almost any file format
- Zamzar http://www.zamzar.com
- eCamm Movie Tools (OS X) http://www.ecamm.com/mac/free/
- VoiceBase https://www.voicebase.com/ Free with sign up audio to text conversion. Uses machine translation so isn't accurate but a good start if you have a lot to transcribe into text.