I'm currently working on a website which has to stream audio files. Since bandwidth is always an issue, the file size should be as small as possible. I wonder what audio formats I should provide. MP3 - Most common format but low quality, I don't know if it's even required, since AAC is well supported by the browsers incapable of playing free codecs MP4 AAC - Nice quality / small filesize, supported by Safari / Mobile Devices / IE9 / Flash / Chrome A free codec - well, until recently, there only was Ogg Vorbis, but Ogg Opus is standardized now and it's really good! Questions: Is it time yet to use Opus instead if Vorbis? Firefox supports Opus since version 15, and Opera has support on its roadmap - I guess Chrome will follow in the future too. Do I still have to provide an MP3 file?