Quote:
Originally Posted by olilarkin
Weirdly if I look at the MP4 in QuickTime player it says it's 5.1 Dolby Digital Plus. If I import it into REAPER there are six channels. Can't for the life of me figure out how to output an MP4 with the proper atmos mix, Although I'm wondering if the extra channels could be magically included in this signal somehow. Any Atmos experts have an idea? Should I be seeing 7.1.2 or 7.1.4, 10/12 channels output?
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For consumer/domestic consumption the Dolby Atmos deliverables are encoded to a 6 channel format using "Dolby Digital Plus with Dolby Atmos" encoding, with "Enhanced AC-e with Joint Object Coding". The encoding is usually lossy listing only 1 bed channel.
This is because, as a pipeline, Dolby Atmos can carry up to 128 channels which can be beds (ready made discrete channel stems) or objects (single point sources with 3D animation data over time). At the other end, in the theater, the Dolby Atmos hardware servers/decoders can support real-time computation and rendering of all the content into up to 64 channels which feed speakers that are available in the theater hall. This happens in real-time depending on the specific speaker configuration of each hall. This huge amount of data is distributed via DCP and MXF standards.
To capture the creative intent and be able to translate it to any listening scenario, Dolby states in their early white papers that in addition to rendering channel-based theatrical deliverables, the Dolby Atmos master file can be used to generate other deliverables such as consumer multichannel or stereo mixes. Via profiling and conditional metadata, Dolby Atmos allow controlled easy renderings to such mixes.
If I understood correctly, you decoded a higher order ambisonic soundfield into a 7.1.2 discrete channel bed. That is probably encoded through the process you used to make the MP4 file into a 6 channel lossy encoded format as the one I describe in the beginning of my port. What you hear is not full 3d object-based audio as you didn't had that information to begin with (again, if I understood your workflow correctly). This is our go to (at SoundFellas my company) for minimum to medium budget film works that want Atmos playback but doesn't really need the separate 3D objects. Only bed is a perfectly viable solution for any production that doesn't include significant 3D sources and will be probably consumed only on mobile/domestic settings.
If you get the 7.1.2 or 7.1.4 test files from here:
https://www.heimkino-atmos.de/Sonsti...und-Testtoene/ you can check it yourself.
I trust the free utility "MediaInfo" from here
https://mediaarea.net/en/MediaInfo to validate the files. And here's what it reports about the audio on the 7.1.4 test file form the link above:
ID : 2
Format : E-AC-3 JOC
Format/Info : Enhanced AC-3 with Joint Object Coding
Commercial name : Dolby Digital Plus with Dolby Atmos
Codec ID : ec-3
Duration : 12 min 20 s
Bit rate mode : Constant
Bit rate : 448 kb/s
Channel(s) : 6 channels
Channel layout : L R C LFE Ls Rs
Sampling rate : 48.0 kHz
Frame rate : 31.250 FPS (1536 SPF)
Bit depth : 16 bits
Compression mode : Lossy
Stream size : 39.6 MiB (22%)
Service kind : Complete Main
Default : Yes
Alternate group : 2
Encoded date : UTC 2016-10-21 00:36:38
Tagged date : UTC 2016-10-21 00:36:38
Complexity index : 12
Number of dynamic objects : 11
Bed channel count : 1 channel
Bed channel configuration : LFE
Hope I helped :-)