PCM track/length problem when creating package with still

[artmit]

Hello,
First, I really want to thanks Carl for creating such fantastic tools!
Recently, used latest version, I encountered strange situation. I needed to create DCP package with still image on the beginning, PCM audio + Atmos aux data for our school's composition department.
On the previous run, for quick checking, I created sound only package (PCM 5.1 + Atmos) and it worked OK, as always
Next I wanted to put still on the beginning with composer name and performance title, faded from black and into black on the beginning. Both 5.1 PCM and Atmos track was set to the same play length, using trim controls and next set to proper positions (in this case 7 seconds).

DCP-still-pcm-atmos.png

After creating DCP and checking in our cinema hall, it played whole composition to the end of Atmos track and then repeats last (about) 10-20 seconds (imo depending on package length) one more time, but in 5.1 PCM only.
When I heard this last fragment was repeated, I checked on our CP850 and it shows on this repetition only 5.1 sound and no Atmos.
I set DCP properties to have 16 channels to disable warning when creating package, but I doubt it has any influence in this situation. I could not check with older versions of DOM if the same happens.
If files would be needed for checking/investigation for Carl I can send such example.

Artur

[Kewl]

Side question: what is your post-production workflow for the Atmos content? Let's say that the Atmos content is done in Avid Pro Tools, what processing is done afterwards so that you can bring Atmos in DCP-o-matic?

My question is triggered by your "school's composition department": I'm in a similar situation and after a year and a half of using a DCP projector and a CP850, I'm still unclear on to how to cheaply manage Atmos content (after Pro Tools) so that I can bring it in DCP-o-matic.

See this ongoing thread: viewtopic.php?t=2110

[artmit]

Hi Kewl,
I teach on Sound Engineering department on our university - we managed to build Dolby Atmos Certified feature mixing studio 2 years ago and we have cinematic renderer commissioned and installed.
Workflow is quite simple: first prepare mix in Pro Tools, then record it into cinematic renderer and record 5.1/7.1 downmix at the same time, encode cinematic Atmos mxf from that Atmos recording. Then, of course, you bring everything into DCP-o-Matic and make proper Atmos DCP package.
On CP850 you need to have Atmos license enabled to play Atmos content, as well you need to have proper Atmos amps/speakers setup in cinema hall.
I'm afraid you cannot cheaply create cinematic Atmos file for making such package, you need to have Atmos certified studio with proper renderer. The other way is to rent Dolby Atmos certified studio, record prepared mix and encode cinematic mxf file in such studio. Due to last year change in licensing of (cinematic) Atmos, every certified studio can make such mix without need to call for Dolby engineer during encoding on site.
Anyway, you can also make Atmos HE mix (atmos file) and encode it into BluRay - you can use Dolby Media Encoder or multiAVCHD to create files needed for BD authoring. Then if you have BD player which can play Atmos/Dolby True HD connected to HDMI input of your CP850 (assuming you have Atmos license on CP850 etc.) you can play such Atmos content. Worth to mention that HE Atmos is slightly different than cinematic Atmos, but for school work it probably will be enough.
A.

[artmit]

Back to the original problem
I did for test 2 packages from material of length 5:57 (min:sec) - first with all "tracks" starting at 00:00:00:00 time, and second with PCM audio and Atmos set to 7 seconds after start.
From what I've checked today, setting position in DoM timing tab for Atmos file does not indeed moves this file into this position. I observed on CP850 it is played at the start time (0:00) of DCP package, not at set in DoM 7 seconds after beginning.
First package played ok from start to end (5:57), second - started playback of Atmos at 0 and switches to PCM at 5:50 (14 seconds before end). Like 2*7 seconds before end... PCM track starts playback at 7 seconds anyway (I checked that using CP850 with "ignore Dolby Atmos" engaged). So it seems when Atmos track was cut/trimmed by DoM at 5:50 decoder switches to PCM at this time.

Maybe it is some limitation of packaging process - to not allow having "non-valid" IAB/Atmos bitstream on the beginning when playback starts? Probably only Carl know answer to this question

Artur

[Carsten]

I would have to look it up somewhere, but I remember there are a few constraints about start offset/timecode relation in order to play ATMOS properly. Offsetting an ATMOS track itself in DCP-o-matic may indeed not work, since the TC for playback timing is baked into the ATMOS track and can not be altered by DCP-o-matic, whereas the other tracks are PCM and can be shifted around without any issues. You may need to have a few seconds offset baked into the ATMOS file itself. But this is just guessing.

[Kewl]

Workflow is quite simple: first prepare mix in Pro Tools, then record it into cinematic renderer and record 5.1/7.1 downmix at the same time, encode cinematic Atmos mxf from that Atmos recording.

Ah, OK, you have the renderer. Thanks.

[carl]

I think Carsten is right here - DCP-o-matic can't create ATMOS silence to put in the gap.

What might work is to have a short reel at the start of the DCP with no ATMOS, and then start the ATMOS sound at the start of reel 2. I'm working on a fancy reel editor which would make this easier, but I think choosing "by video content" for reel mode should do the right thing. It would be interesting to see if that works.

[artmit]

It indeed was the last-minute solution I selected - because I had only 90 minutes before presentation/concert I needed to act quickly to prepare 10 reels When I previously created those reels with stills I just wanted to have nicer effect, when sound would start after nice fade in and then have nice fade out. Of course, it can be done in 2 reels separately, as you mentioned (which now I know it is only way).
Thanks for confirming/explanation, your note about "creating Atmos silence" is key point here. Maybe it would be nice to have such warning when Atmos sound is not positioned at 00:00:00:00 on the reel.
BTW. Is that possible to "cut" Atmos soundtrack in D-o-M and position it on timeline one next to another? Assuming they have identical metadata set (no change in beds/object configuration) would it be this way concatenated? I ask because I just thought about creating such "silence" as additional file ti put it before real Atmos sound in cases like this.

[carl]

I made a note in the bug tracker to warn about cases like this. I'm glad you found a solution!

I think perhaps a "cut" might work - DoM basically works with what the underlying `asdcplib` calls "frames" (i.e. chunks of ATMOS data that are 1 video frame in duration). But I have no way to test this stuff so I'd be interested to hear how you get on if you try it!

[artmit]

Great! I will try that on earliest possibility, unfortunately our studio is kind of busy at the end of semester