How AAC / M4A to OGG / Vorbis conversion works
AAC / M4A decode → normalized audio stream → OGG / Vorbis encode
Reading AAC / M4A
AAC or M4A input is demuxed from its supported transport or MP4 container with compatible tags.
Creating OGG / Vorbis
OGG / Vorbis output provides open lossy audio with compatible comments and artwork.