Determine whether Dolby Atmos file is channel-based

Question

So I'm a bit confused over this. It seems like Dolby Atmos formats (e.g. AC4, eac3) are advertised as object based and thus can adapt to the listening environment/setup, but from experimenting with some files I downloaded it seems like they are in traditional 5.1 channel format (at least when decoded and viewed). How can I determine if a Dolby Atmos encoded audio file is object-based, channel-based, or a mix of both?

Example output:

mediainfo /Users/jin/Desktop/Music/Stem\ Separation/Tidal/Joe\ Hisaishi\ -\ Dolby\ Atmos/Songs\ of\ Hope-\ The\ Essential\ Joe\ Hisaishi\ Vol.\ 2\ \[209256235\]\ \[2021\]/CD1/07\ -\ Joe\ Hisaishi\ -\ DA-MA-SHI-E.m4a 
General
Complete name                            : /Users/jin/Desktop/Music/Stem Separation/Tidal/Joe Hisaishi - Dolby Atmos/Songs of Hope- The Essential Joe Hisaishi Vol. 2 [209256235] [2021]/CD1/07 - Joe Hisaishi - DA-MA-SHI-E.m4a
Format                                   : MPEG-4
Format profile                           : Base Media / Version 2
Codec ID                                 : mp42 (mp42/dby1)
File size                                : 43.2 MiB
Duration                                 : 7 min 50 s
Overall bit rate mode                    : Constant
Overall bit rate                         : 769 kb/s
Encoded date                             : UTC 2022-02-01 20:48:09
Tagged date                              : UTC 2022-02-01 20:48:09

Audio
ID                                       : 1
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                                 : 7 min 50 s
Bit rate mode                            : Constant
Bit rate                                 : 768 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)
Compression mode                         : Lossy
Stream size                              : 43.1 MiB (100%)
Service kind                             : Complete Main
Default                                  : Yes
Alternate group                          : 2
Encoded date                             : UTC 2022-02-01 20:48:09
Tagged date                              : UTC 2022-02-01 20:48:09
Complexity index                         : 16
Number of dynamic objects                : 15
Bed channel count                        : 1 channel
Bed channel configuration                : LFE

Note that it both gives me 6 channels and 15 dynamic objects, which is confusing to me (but probably not to those familiar with the format).

If it turns out that an audio file is object-based, how can I extract the individual objects, or convert it to ADM BWF master file (so that I can import it into Logic)?

Answer 1

For eac3, look for JOC or Joint Object Coding. In Dolby Reference Player, you should see Dolby Atmos: Yes which means this is object-based audio.

For AC4, note that all (if not most) of the sources available are in IMS-Atmos. This is essentially "fake" atmos because this is not object-based; rather, it's in stereo with extra information for binaural rendering. I do not know of any publicly available software that can decode AC4 other than Dolby's own reference player.

For a player that can fully decode object-based eac3 and convert it to other formats, including ADM BWF, check out Cavern.

For more information on the encoding of object-based eac3 file, check out this article.