An SPX file is a Speex audio file saved within an Ogg Vorbis container. Speex is an open source patent-free audio format designed for speech compression. It supports variable bitrate (VBR) encoding and several features not found in other audio codecs. Some examples include embedded encoding, intensity stereo encoding, and voice activity detection.

Dolby Digital film format, developed for encoding audio tracks for films. It supports up to 6 audio channels: left, right, front, rear, upper and lower. Because of this, it allows you to store “3-dimensional” audio tracks. It’s widely used both in movie theaters and by the users themselves for storing audio tracks in film libraries at home.