About Dolby Atmos in Dcpomatic

[nimes]

"I've gone through the help document of DCP-o-matic but couldn't find a way to make a DCP with Dolby Atmos audio. I've been provided with an Atmos IAB MXF file rendered via Dolby RMU and 7.1-channel audio. Can somebody guide me through the procedure to package it in DCP-o-matic?"

[IoannisSyrogiannis]

There is none, because the IMF and the DCP files are different. Read more here: https://dcpomatic.com/forum/viewtopic.php?p=11036

User izwb003 wrote that he created a solution here: https://dcpomatic.com/forum/viewtopic.p ... 671#p11671
Yet, that is not a solution incorporated in DCP-o-matic. Therefore, you need to use a DCI IAB .mxf file for use with the program.

Best of luck and be so kind to let us know about the results.

Edit: I read again, and I see that, while you mention both "Atmos" and "IAB", you write nothing about "IMF" or "DCP". I am presuming, maybe erroneously, that you have the IMF version and that is why you are not able to use the file. I don't want to speculate any further, but if there is more there to consider, please share.

[nimes]

Thanks for the reply Ioannis. The dolby atmos audio I have is DCI IAB MXF, its for cinema not IMF. IMF is for streaming platform I guess.

[carl]

If your MXF is already in the right format you should be able to add it like any other content and it should be listed as "[ATMOS]" in the file list...

[IoannisSyrogiannis]

I miss the "like" button that is available on other forums, to declare agreement without posting.
I agree with both the posters above and -given the opportunity- I wanted to write that I assumed that nimes tried to add the IAB file, it didn't work, and -thus- the post.

So, if (presumably) the above didn't work and the file is not made for IMF, but for DCP, could it be that the original DCP is somehow edited in terms of duration?
I wonder. What happens when a SMPTE DCP has the IAB/ATMOS essence on one of the reels, for localization purposes?
(If for instance a distributor, or a supporter, such as MEDIA in Europe, added their logo among those incredibly long starting credits that are injected.)
Would that work as is, or would it be necessary/compatible/advisable to introduce dummy-IAB/ATMOS assets for the rest of the reels, just like one would better do with SMPTE subtitles?

And, expanding on that, if we are not talking reels, but a unified final video asset, may the IAB/ATMOS MXF file be used with a non-zero entry point, or would that "break" things? (Subtitles is, once again, the counterexample, where non-zero entry points are not according to standards. On further searching, all reel elements, including subtitles and aux data should have the same duration, according to SMPTE RDD 52)

Looking into the matter, on SMPTE standard 429-18 of 2019 it reads (altered the text for focus on the subject and highlighting):
First Frame specifies an edit unit for alignment with the beginning of the associated image sequence of the picture track.
The value for First Frame is set during initial bitstream coding and should not be changed.
This doesn't answer all my questions, but gives some idea of what one may or may not do with a ready-made file.

So, if things don't work by just adding the file, one of the reasons could be that the DCP structure for which the IAB/ATMOS file was made is different on that aspect from the intended structure.

[edgecode]

I tried to build a DCP from scratch using theatrical ATMOS MXFs. The caveat is there are reels. I was able to bring all media in and align it but the rendered DCP only has what look like ATMOS Reel 1 and one more much smaller ATMOS MXF for which I don't see a match in the source. All other assets seem to be present but the Player craches.

[IoannisSyrogiannis]

It seems to me like (and I might very well be wrong here) that for the sake of creating reels, DCP-o-matic is manipulating the length/duration of the IAB file. Something that is prohibited in practice and fails.

If you have two Atmos files in your result, it seems to me that this is a two-reels original DCP that takes advantage of the one and only IAB MXF file.

So, given the fact that DCP-o-matic is not built in a way that allows non-destructive editing or headers, feet, entry points, duration etc. I would try to manually edit the CPL in a way that would allow me to use the original, full IAB MXF with the proper entry points and durations that will be in accordance to the video parts.

Otherwise, you will need an authoring program that allows using and reusing a single file unaltered in reels.
DCP-o-matic could probably do that, only in order to make a VF, not while making a DCP from scratch.

If you figure it out, write a line for the community's benefit.

[edgecode]

I have seven ATMOS MXFs, seven separate reels. The first one gets correctly incorporated into the DCP. The rest do not.

[carl]

Do you have the reel mode set to "by video content" in the reels dialog?

[edgecode]

Yes and all looks aligned. I had to trim the head of the first ATMOS reel and the tail of the last because they have Academy leaders.

reels.png