The Advanced Authoring Format (AAF) is a professional file interchange format designed for the video post-production and authoring environment. It was created by the Advanced Media Workflow Association. The AMWA develops specifications and technologies to facilitate the deployment and operation of efficient media workflows, working closely with standards bodies like the SMPTE.
this format is free, which apparently is one of the reasons for its popularity. The used codecs supports variable bit rates (as a default), and .ogg files usually play back easily on all platforms. All things being equal, the sound quality exceeds that of mp3 somewhat.