Overview: Dolby lossy codecs
Dolby lossy audio formats define distinct coded signals with their own channel, metadata and decoding arrangements.
AC-3, E-AC-3 and AC-4 are separate formats, not interchangeable names for one encoded track. Their pages explain the signal and metadata associated with each. That information is useful when interpreting an Emby track choice or the change from direct audio delivery to conversion.
Dolby Digital (AC-3)
Dolby Digital, also called AC-3, is a lossy audio format supporting mono, stereo, and surround presentations.Dolby Digital Plus (E-AC-3)
Dolby Digital Plus is the Enhanced AC-3 lossy audio format used for multichannel and compatible immersive delivery.Dolby AC-4
Dolby AC-4 is a lossy audio system supporting channel-based, immersive, and personalized presentations.