About Dolby Atmos in Dcpomatic

[carl]

Yes, it does say FSKSync in the right position. However it might have been a stupid suggestion on my part because it says somewhere in white papers the tag should be limited to fewer characters than this.

Do you have a link for that?

[carl]

Exactly the same error with the new build.

It could also be something to do with the metadata in the PCM MXF file. At some point I became convinced that some channels (including the ATMOS/IAB sync channel) should not have a sub descriptor in the PCM MXF. Maybe I was wrong about that. @carsten it would be interesting to see the plain PCM audio MXF from any examples you have with ATMOS

[edgecode]

Here is the discussion about the character limit.

https://github.com/SMPTE/st429-16/issues/8

As for sub descriptors, I think Netflix specs explicitly say "do not include"

https://partnerhelp.netflixstudios.com/ ... quirements

[StephW999]

DCP Dolby Atmos (with 7.1 pcm backup reverted) :

<cpl-meta:MainSoundConfiguration>71/L,R,C,LFE,Lss,Rss,-,-,-,-,Lrs,Rrs,-,FSKSync,-,-</cpl-meta:MainSoundConfiguration>
....

<mca:MCASubDescriptors xmlns:mca="http://isdcf.com/ns/cplmd/mca" xmlns:r0="http://www.smpte-ra.org/reg/395/2014/13/1/aaf"
...
<r0:AudioChannelLabelSubDescriptor>
<r1:InstanceID>urn:uuid:83fda4e7-4ecf-41e2-a2e5-965964a0bb0e</r1:InstanceID>
<r1:MCALabelDictionaryID>urn:smpte:ul:060e2b34.0401010d.03020110.00000000</r1:MCALabelDictionaryID>
<r1:MCALinkID>urn:uuid:43b56517-a524-4fb0-8ba1-4b04136c6422</r1:MCALinkID>
<r1:MCATagSymbol>chFSKSync</r1:MCATagSymbol>
<r1:MCATagName>FSK Sync</r1:MCATagName>
<r1:MCAChannelID>14</r1:MCAChannelID>
<r1:RFC5646SpokenLanguage>en</r1:RFC5646SpokenLanguage>
</r0:AudioChannelLabelSubDescriptor>
</mca:MCASubDescriptors>

[Carsten]

BTW- there are two opposing 'movements' with ATMOS DCPs currently. While ISDCF/RDD52 actually mandated for ATMOS CPLs to have NO mainsound (fallback) at all (channels silent), I have yet to see an ATMOS DCP following that recommendation. Seems that having a usable fallback for a complex object based audio rendering system is still preferred.

Now, recently I see mainstream high profile ATMOS DCPs to have fallback mainsound in 5.1 only, but NOT indicating it in the CPL name, e.g.

AvatarFireAsh_FTR-TXTLS-2D-48FPS_S_DE-XX_DE_IAB_2K_TCS_20251205_WDS_SMPTE_VF contains 5.1 in mainsound.

But this CPL actually DOES have a 7.1. fallback in mainsound:

WickedForGood_FTR-2-2D_S_EN-DE_DE_IAB_4K_UP_20251030_PXU_SMPTE_VF

cpl-meta:MainSoundConfiguration>71/L,R,C,LFE,Lss,Rss,-,-,-,-,Lrs,Rrs,-,FSKSync,-,-</cpl-meta:MainSoundConfiguration>

On the other hand, we see some distributors/studios now distributing IAB/ATMOS CPLs as the ONLY package offering 7.1 in order to have a smaller distribution inventory. Most if not all servers allow to ingest ATMOS/IAB CPLs and play the fallback mainsound even on non-ATMOS systems. I understand Deluxe and ISDCF advises to NOT do that, but, I looks as if pragmatic considerations overrule this advice.

But very often, IAB/ATMOS fallback is only 5.1, even if there is a separate 7.1 VF available. That seems to be the common method for the big US studios now - but not for all:

TheHousemaid_FTR_S_EN-DE_DE_IAB-71_4K_LEO_20251107_CPP_SMPTE_VF

Again, IAB-71 are the only 7.1 CPLs available for this title (in Germany)

Same here:
ThePhysician2_FTR-1_S_DE-XX_DE-NR_51_4K_CFV_20251110_WFG_SMPTE_VF
ThePhysician2_FTR-1_S_DE-XX_DE-NR_71-Atmos_4K_CFV_20251110_WFG_SMPTE_VF
ThePhysician2_FTR-1_S_EN-DE_DE-NR_71-Atmos_4K_CFV_20251027_WFG_SMPTE_VF

Now, as long as you consider mainsound in ATMOS/IAB CPLs as a fallback option only, it is certainly interesting to know how common ATMOS/IAB systems react in the fallback case - will they always fall back to 5.1, or will they follow the mainsound configuration indicated in the CPL? The latter would certainly be preferred method, if e.g. a 7.1 fallback is present in mainsound.

As a side note - in order to keep CPL inventory low in Germany, Disney decided to not make separate 7.1 VFs available for AVATAR-III - they could have included 7.1 mainsound in their ATMOS/IAB CPLs, but decided against it. As a result, no 7.1 CPLs of AVATAR-III were available in Germany (though, in other markets). Only 5.1 and IAB/ATMOS was distributed.

[edgecode]

For this particular DCP it is 5.1 in OV and 7.1 in VF. And it goes to Deluxe for QC.

[Carsten]

@carsten it would be interesting to see the plain PCM audio MXF from any examples you have with ATMOS

Hi Carl, I just sent you an email with a download link to some current trailers.

[StephW999]

An example in France of a deluxe DCP for the film “The Housemaid” :
A unified package that merges all assets.
The CPL IAB has its silent PCM tracks. for me is problematic, because if the atmos failed on the audio processor then
the fallback is on silent tracks (this happened to me)

FemmeDeMenage_FTR_S_EN-FR_FR_51_4K_MET_20251203_DLX_SMPTE_OV
<cpl-meta:MainSoundConfiguration>51/L,R,C,LFE,Ls,Rs,-,-</cpl-meta:MainSoundConfiguration>

FemmeDeMenage_FTR_S_EN-FR_FR_71_4K_MET_20251203_DLX_SMPTE_OV
<cpl-meta:MainSoundConfiguration>71/L,R,C,LFE,Lss,Rss,-,-,-,-,Lrs,Rrs,-,-,-,-</cpl-meta:MainSoundConfiguration>

FemmeDeMenage_FTR_S_EN-FR_FR_IAB_4K_MET_20251203_DLX_SMPTE_OV
<cpl-meta:MainSoundConfiguration>51/L,R,C,LFE,Ls,Rs,-,-,-,-,-,-,-,FSKSync,-,-</cpl-meta:MainSoundConfiguration>

[Carsten]

We have just received the same movie - also with an ATMOS+7.1 VF. I have yet to hear wether mainsound is silent here in Germany. We have not yet received our KDM. I guess if it had silent main sound, it wouldn't be marked IAB-71 .

- Carsten

[carl]

@edgecode I am still wondering why EasyDCP raises the error about channel 14. Maybe you could try making a DCP using only SMPTE Bv2.0? Then there will be no audio channel subdescriptors in the PCM MXF. DoM normally writes these (but not for the sync track, for reasons that I'm not clear about).

You can go into the "non-standard" prefs tab and tick "Allow use of SMPTE Bv2.0". Then in the DCP "Standard" dropdown you should have SMPTE (Bv2.0 only) as an option.