About Dolby Atmos in Dcpomatic

[edgecode]

Standard drop–down is greyed out. Shall I start a project from scratch?

[carl]

Sorry, that's a bug which should be fixed here.

[edgecode]

Thanks.
I switched and rerun the job again.

Code: Select all

'Application Profile' metadata extension missing for CPL

MCA Sub Descriptors missing for CPL 

Sound Track Files shall signal Wild Track Format (SMPTE 429-2 Channel Configuration 4)

[edgecode]

The player seem to recoognize them correctly though.

Screenshot 2026-02-16 at 12.35.24 AM.png

[carl]

OK, maybe what it wants is something looking more like SMPTE Bv2.1 but with no MCA subdescriptors in the MXF (but in the CPL), and WTF rather than 51 in the MainSoundConfiguration. Let me hack you a build that does these things, and then if it fixes the warnings we can try to work out who's actually right here

[carl]

Here is a build with those tweaks if you have time to test. Thanks for your patience!

[Schmidt]

So what is really going on with the IAB packaging this year?

Many high profile releases use IAB CPL without any mention of fallback tracks. As previously stated, some actually have 5.1 or 7.1 fallback track.
(why anyone would use a 5.1 over 7.1 fallback for IAB is beyond my comprehension but another discussion)

And then we have IAB with silent fallback channels that will just go to silence when the playback fails. I don't really understand the reasoning behind not including a fallback track to at least save the screening if the IAB playback fails, but seems like several high profile releases are done this way now. All or nothing.

Do we have any clue what is the correct way to go about packaging a DCP with IAB in 2026?

[Wolfgang Woehl]

The intent is to avoid silent failure of a IAB renderer and silent fallback but rather <pun incoming> to fail with silence. Worries were that a failing renderer could go unnoticed etc.

I don't know how systems in the field actually handle these bipolar-compositions, with content signal in MainSound and IAB, what options they offer for operators - do you have a big red button that says "IAB off"? Is there recovery? Automatic/manual?

A composition, as per Interop/SMPTE, was never intended to be a cloud of options. It would be trivial for content authors to deliver two distinct compositions: one with IAB and one with MainSound 5.1/7.1. That should be the "fallback".

I had a lot of fun with IAB stuff this week. In the dcp_inspect player you can switch from IAB to MainSound if there is content signal in there. But for IAB compositions the audio defaults to... IAB, what else

[barber]

I don't know how systems in the field actually handle these bipolar-compositions, with content signal in MainSound and IAB, what options they offer for operators - do you have a big red button that says "IAB off"? Is there recovery? Automatic/manual?

On the Dolby CP850, we have several macros : "Atmos only" (fallback to silence), "7.1 + Dolby Atmos" (automatic fallback to MainSound)... The web UI clearly indicates when the IAB signal becomes "unavailable" and when MainSound is being used. An "Ignore Atmos" button is also there to manually switch to MainSound if the active macro enables it.

Currently I see many major features from Deluxe and others where MainSound is not intended as a fallback for an IAB error but rather as a replacement when a reel (usually a logo) doesn't have an IAB asset. Consequently such CPLs don't follow the SMPTE requirement to have an Aux asset on every reel. I wouldn't call that "the correct way to package a DCP with IAB" but it's a fairly common usage.

[Wolfgang Woehl]

Huh, interesting. Does "IAB unavailable" happen? Often or rarely? Is this kind of notification and automatic switchover specific to the Dolby CP850 line? Will the CP850s "recover" automatically? Do other devices have these capabilities?

Very interesting, your observation of current practice wrt logos/idents, with MainSound content signal (or are these always silent?) and without IAB. And your CP850 would automatically switchover at the reel boundary?

SMPTE (and RDD 52 as well) says "should" (preferred/recommended), not "shall" (mandatory), wrt AuxData presence consistency throughout reels. Big difference. So, spec-wise these compositions are ok. I'm just seeing an interoperability issue - behaviour like automatic switchover or ignoring or failing silently is not specified/defined, to the best of my knowledge.

Do these compositions play correctly on all systems in the field?