Engine supports media files containing Dolby Digital and Dolby Digital Plus. WAV, MXF, MP4, QT MOV and MPEG TS files that contain common formats of Dolby Digital/+ can be processed in Engine for Loudness Compliance. Profiles for the loudness settings can be created for Dolby Digital/+ in the same was as for PCM audio, and with the same flexibility.
Although as of November 2018 Engine can only support Loudness Compliance for Dolby Digital/+, full encode and decode will be adding during Q1 2019, after which the full range of Engine capabilities will be available in conjunction with Dolby Digital/+.
Dolby Digital/+ is carried in a pair of channels in the media file. This means that the equivalent of a stereo pair in the file is used to hold the Dolby encoded audio. Dolby Digital/+ is most commonly used to carry a 5.1 track. Additional audio channels that are associated with the 5.1 can also be carried. Note that ‘associated’ in this case has a special meaning. It requires that the extra channels are related audio, so you could have a stereo version of the same audio also included in the Dolby Digital/+. However you could not carry a completely independent stereo along with the 5.1 and this is because the associated channel is matrixed with the 5.1, which is a similar concept to how the original Dolby analog audio was matrixed.
If you need to carry an unrelated stereo along with the 5.1, then this would have to be carried separately. Engine would require that the stereo and the 5.1 were each independently encoded, and so this scenario would need four PCM channels to contain the encoded audio.