Atmos track best practices

[DangerousCinema]

I have a short DCP containing both an Atmos Cinema audio track and a standard 7.1 audio track (which is used as a fallback for systems without Atmos support).

This DCP works very well, and it does play the Atmos track when deployed on an Atmos-Cinema-Certified system.

I want to keep those two audio tracks (Atmos + standard 7.1 audio) as they are but I want to replace the video track with a new one.
I have been able to create a working DCP containing the 7.1 audio track and the new video track, but I am not able to carry the Atmos track into it.

What would be the best practices to produce such a DCP containing an Atmos-certified track using DCP-o-matic ?

[gunnar]

Dolby Atmos is not open source standard.
And technically the Atmos track is not a sound file.

I am not going to speak on behalf of Carl, the developer of DoM but create/packing Dolby Atmos DCP with DCP-o-Matic won't be possible, ever. Unless Dolby will decide to release their secret recepy and give Atmos out as open source standard. But I doubt Dolby will do that.

Best regards,
Gunnar

[carl]

What happens when you try to make the new DCP containing the atmos track? How did you do it?

[Carsten]

ATMOS is now just a proprietary Dolby brand for SMPTE standardised IAB bitstreams. Not saying that IAB audio support could be implemented easily in DCP-o-matic, but proper file handling could at least be possible, as that is part of SMPTE DCP/aux data.


Carl, have you ever seen an ATMOS DCP? There are unencrypted ATMOS trailers available.

I don't know how exactly an ATMOS aux data file is associated with the CPL/playout process. There is, of course, an audio time code track in the DCP audio asset, and a TCP transfer process from the server to the ATMOS audio processor.

Finding out probably means a lot of reading.

[gunnar]

What happens when you try to make the new DCP containing the atmos track? How did you do it?

I know this is not question for me but I am pretty sure that the OV with the short film that he talks about in the beginning is definitely made with something else than DCP-o-matic. (Clipster or Dolby's CineAsset)
Because Dolby Atmos is not open source standard, then what is happening is when he tries to re-wrap the existing Atmos DCP with DCP-o-Matic then he end up with just regular 7.1 DCP since DoM don't even know the Atmos track was there in the first place.

So I think the only way DCP-o-Matic could re-pack DCP and keep the existing Atmos track is if DoM could read the Atmos track and know what it is. And I don't think that will ever be possible meanwhile Atmos isn't open source.

[DangerousCinema]

What happens when you try to make the new DCP containing the atmos track? How did you do it?

The first thing I did was to study how the Atmos DCP I'm working from was made. Basically, it's like a normal DCP but it has an extra MXF track in addition to the audio and video MXFs. The audio MXF is presented as being 7.1 but the underlying file contains 16 tracks. That extra Atmos MXF file is listed in the Assetmap XML, where it's referenced as the a "chunk", just after the audio "chunk", but before the video one.

Here are the 3 strategies that seemed to have some potential in my tests so far:

Create a new DCP from scratch by importing my new DPX sequence as a video source, combined with the Atmos MXF and the 7.1 Audio MXF. I used the "Add file" function in DCP-o-matic to import the those 2 files, and "Add Folder..." for the DPX sequence. The Atmos track does load, and it has ATMOS written in brackets at the end of its name once loaded in the "content" window of DCP-o-matic. That Atmos track does not have an "audio" tab: it only had timing. I did check the timing and made sure all files were starting on the first frame - they do by default. The Atmos track also has the proper duration (00:01:25:09) when I import it. If I try to open the timeline though it will crash most of the time, giving me an error message telling me to send Carl (that's you I think !) an email about this : timeline_content_view.cc:45
image of error window that opens twice after such a crash: https://imgur.com/JsSI4WO
Also, after such a crash, or simply after closing DCP-o-matic, if I reload the project later the Atmos track will still show up, but with a different duration: 1639:28:46:00. Or sometimes it shows only zeroes. To fix the duration I have to remove the Atmos XMF from the content list and re-import it.
If I render a DCP from this project, I get a working DCP with 7.1 audio MXF containing 16 tracks, but no sign of an Atmos MXF whatsoever.

Create a new DCP from scratch by importing my new video track as a MXF (so no re encoding is required for the video) and matching it with the Audio and Atmos MXFs from the original working version. This gives the exact same result as above: it produces a working DCP, but the Atmos track is nowhere to be found.

Load the original working DCP containing the Atmos track and replace the video track with a new one in the timeline. I was wary about working with the timeline since I had experience so many crashes when I tried that after having loaded an Atmos MXF, but if I load those as a DCP instead (using the "Add DCP..." function) then it works well. The Atmos track doesn't show per se on the time: you can only see the video and the audio track there. But I was able to change the video track by putting my new video MXF over the old one, and not touching anything else. This also produces a working DCP, but without the Atmos track once again, just the 7.1 audio is there, sadly. If I try to do the same procedure but with "Use this DCP audio as OV and make VF" it creates a DCP without any audio track, not even as a reference in the Assetmap.xml.

If I load the resulting DCP in DCP-o-matic player, and apply the "verify DCP" function it tells me "DCP validates OK".

If you think it might help you, I can send you the Atmos certified DCP file I'm working from. It's just under 2GB.

[DangerousCinema]

I don't know how exactly an ATMOS aux data file is associated with the CPL/playout process. There is, of course, an audio time code track in the DCP audio asset, and a TCP transfer process from the server to the ATMOS audio processor.

There are indeed a few different specialized channels in there besides the audio track proper. For example, channel 13 is used to sync D-Box systems. Here is a document from the ISDCF describing those channels:
https://isdcf.com/papers/ISDCF-Doc4-Aud ... ations.pdf

[carl]

DoM has supported packaging of existing Atmos MXFs for a while, so this should be possible.

If you could send me the ATMOS MXF I can try it. I just did a test with an ATMOS file I have here and it was passed through into a new DCP OK. Any of your approaches should work fine.

I would suggest working with the latest test version as I'd be more inclined to fix bugs in that version than 2.14.x.

That Atmos track does not have an "audio" tab: it only had timing

That's to be expected; you can't alter anything about the sound, but you can move it around and trim it.

[DangerousCinema]

Thanks a lot for your support ! I will install the latest test version, make some more tests and let you know how it goes - I had been using realease 2.14.55 so far.

I would also like to send you the Atmos DCP but I would prefer not to make it publicly available. Is there any way I can send you a private message with the download link ?

[carl]

Sure: carl@dcpomatic.com

You could make sure it doesn't work with 2.15.x first, if you like.