.ogg
Ogg audio
An open container from the Xiph.Org Foundation. An .ogg file usually holds Vorbis, a free lossy audio codec, though the container can carry other streams.
Game sound, open-source software and music where a royalty-free format is wanted.
Opens in VLC, Firefox, Chrome, Audacity, foobar2000
About OGG files.aac
AAC audioAdvanced Audio Coding
A lossy codec standardised by MPEG in 1997 as the successor to MP3, usually sounding better at the same bit rate. A bare .aac file holds the raw stream without an MP4 wrapper.
Streaming audio, digital radio and soundtracks taken from video files.
Opens in Music, QuickTime, VLC, Windows Media Player, most phones
About AAC files