Massive progressive sync drift when converting DDP Atmos (E-AC-3 JOC) to ADM

[AntPradZT]

Hello! First, I want to reiterate my gratitude for the incredible work you do on Cavernize. It is an amazing tool that I use constantly.

I am opening this issue regarding a specific problem I encounter when converting DDP Atmos (E-AC-3 JOC) files to ADM for ProTools/Nuendo.

Context:
When I convert TrueHD Atmos from Blu-ray MKVs, it works perfectly about 95% of the time (with the only exceptions being some Disney/Pixar seamless branching dropouts maybe). However, when dealing with Web-DL series that only exist in DDP Atmos (like Stranger Things or The Witcher), the conversion systematically fails due to a massive progressive desynchronization.

The Issue:
The generated ADM file drifts further and further out of sync with the video as the file plays. Because the object panning automations are baked into the ADM at those specific timestamps, it is impossible to manually fix the sync in the DAW later by just stretching the audio.

Test Cases & Evidence:
I tested this with the latest version of Cavernize on two different Windows 11 PCs, and it happens across all seasons of these shows. Here are three precise examples (I have screenshots from ProTools comparing the reference stereo track to the imported ADM if needed):

Example 1: Stranger.Things.S04E01.Chapter.One.The.Hellfire.Club.1080p.NF.WEB-DL.DDP5.1.Atmos.x264-TBD

At the very end of the episode (on the final Netflix logo), the ADM audio is delayed by exactly 4 minutes, 27 seconds, and 3 frames compared to the reference video audio.

Example 2: Stranger.Things.S04E07.Chapter.Seven.The.Massacre.at.Hawkins.Lab.1080p.NF.WEB-DL.DDP5.1.Atmos.x264-TBD

At the end of the episode, the ADM audio is delayed by exactly 5 minutes, 43 seconds, and 1 frame.

Example 3: The Witcher Season 1, Episode 1

Similarly, at the very end of the episode (on the final Netflix logo), the ADM audio progressive drift reaches exactly 3 minutes, 32 seconds, and 8 frames.

Given the massive size of the drift and the fact that it happens across entirely different shows, I humbly suspect there might be an issue with how the DDP decoder handles the sample rate, framerate, or frame interpretation during the ADM generation.

I can provide the ProTools screenshots to show the exact waveforms if it helps. Thank you so much for your time and for looking into this Bence!

[AntPradZT]

[VoidXH]

Was this working in any previous version?

[AntPradZT]

Hi Bence,

To answer your question: I have actually never managed to get this far with DDP conversions before. Up until today, I have been doing everything using TrueHD.

Back in the day, before TrueHD was fully supported, I did try to convert DDP files but without success. At that time, the audio channels were completely mixed up and the sound was heavily distorted/clipping (it sounded a lot like a sample rate issue). I remember you mentioning back then that it worked fine with short videos like the Dolby Atmos demos, but I personally never managed to get a full-length DDP movie or episode to work.

So this current version is actually the furthest I've ever gotten with DDP, as the audio quality and channel routing are now perfect! It's just this progressive sync drift on long files that remains.