Audio Sync Issue with 4K DCPs - Seeking Advice

[glbirdsong]

Hi everyone,

Long-time lurker here and a proud user of DCP-o-Matic for over two years! At our theater, we use DCP-o-Matic for every single screening. On average, I work with the program 20–30 times a month, and it has been an absolute game-changer for us. I’ve never encountered any issues—until now.

Previously, I’ve always ripped Blu-rays using MakeMKV and then dropped the resulting files into DCP-o-Matic. This workflow has been flawless for two years. Recently, however, we upgraded our cinema system to 4K, which included upgrading to a flashed Pioneer 4K UHD disc drive. Everything seemed to be working great with the new setup.

I tested a 4K DCP briefly, and it appeared normal. However, during a screening last night, an audio sync issue was reported about 30 minutes into the film. Unfortunately, I wasn’t on-site to witness it myself. I’ve since requested more details from our team to better understand the extent of the problem—whether the audio is just a few frames out of sync or several seconds off.

Naturally, I’m now concerned that all our 4K DCPs may have the same issue. For context:
• The original content’s frame rate is 23.9760 FPS.
• The DCP is running at 24 FPS, with the content speed adjusted to 100.1%.
• This same configuration worked perfectly for our previous 1080p DCPs.
• The MKV file plays in perfect sync on VLC.

After skimming through the forums for advice, I updated DCP-o-Matic to the latest version in hopes that this might resolve the issue.

I’m waiting for more details on what the patron noticed, but in the meantime, I’d love to hear any thoughts or suggestions. Has anyone experienced a similar issue with 4K DCPs? Are there any steps I should take to prevent or fix this audio sync issue?

Thanks in advance for your help!

[Kewl]

I've made many DCPs from MKV files ripped from UHD Blu-rays. Never had a problem with de-synched audio, whether the original audio was DTS-HD MA or Dolby TrueHD/Atmos. Since these are test DCPs, I always use the latest test version of DOM. Maybe my lucky streak is due to the DOM test version.

The projection gear: Barco SP4K-12C (Barco ICMP-X) with Dolby CP-850.

From my end, the biggest challenge is going from HDR/WCG to the DCP color space: I'm still experimenting on that front...

[carl]

It would be interesting to know if the same glitch appears each time you play the DCP (you could just skip through to a little before, and play it).

Perhaps you could also send the log from your DCP-o-matic project folder to carl@dcpomatic.com in case there is something interesting there.

[Carsten]

I think it's important to first find out two possible reasons:

- the audio is indeed not in sync on the DCP/file level - which would obviously be a DCP-o-matic bug
- the audio is not in sync at playback time/right from the start/later in the DCP/constantly/also if you stop and restart play - that could still be an issue with DCP-o-matic, or the playback system, or a combination

I assume this 4k DCP was created from a 4K UHD disk?

I guess you need to spend some time with this DCP on your system to find out what is going on. What server and projector is used, and which datarate was set in DCP-o-matic for J2K compression?

Was the DCP actually ingested onto the server and played from there? Because some servers allow to play DCPs directly from an external disk.

[Kewl]

Come to think of it, I can get audio desynced on DCPs made with DOM. But at the time I noticed, I attributed the desync to the projection system.

Capture d’écran, le 2024-12-05 à 08.38.43.png

Is something similar happening here?

[IoannisSyrogiannis]

Come to think of it, I can get audio desynced on a DCP made with DOM. But at the time I noticed, I attributed the desync to the projection system.

AlchemyAudioLagIssue.png

Is something similar happening here?

It's been a couple of years (?) that that issue has been addressed. I can't claim that it disappeared, but it did make life a lot easier.
First thought was that, though. And a lot of info missing.

[Kewl]

And a lot of info missing.

From the OP or from me ?

[IoannisSyrogiannis]

From the original poster, in order to narrow the problem down. (It was an affirmative statement, in relation to what was mentioned before.)