Pitch shifting down

[neruson]

Hi everyone,

Having an issue with DCP-o-matic 2.18.35.
I exported a 1920x1080 video in Apple ProRes 422 @24fps and Uncompressed audio, 48Khz 24-bit.

When bringing it into DCP-o-matic the video playback looks fine, but the audio is slightly pitched down. When I created the DCP regardless of the issue with playback, I brought it into the DCP-o-matic Player app to test playback. Same issue. Pitch is still lower.

Now, I've run several tests, converted the DCP audio into WAV so I could play it back and confirm whether the audio on its own is still pitched down, but it wasn't - it played normally.

I have an upcoming screening at a major cinema chain and need to ensure this is just a playback issue with the app and not an issue with the actual DCP. I'm trying to confirm with the cinema that the audio in their testing is not sounding pitched down...but it's hard to be 100% certain when they aren't familiar with the video/audio content.

Is there potentially an issue with the DCP-o-matic app running on my 2025 Mac Studio M4 Max, on Sequoia 15.6.1?

Thanks in advance!

[barber]

Hi,
Is the audio output device used by DCP-o-matic the same than when you play the WAV?
To make sure there is no change you can load both the master and the audio MXF from the DCP in an audio editor timeline and compare the waveforms. You can visually compare or you can invert phase of one audio and listen to the mix: if the result is silent, both audio are identical.
You can also use ffmpeg to do that with something like:

Code: Select all

ffmpeg -i "source-audio.wav" -i "dcp-audio.mxf" -filter_complex "[1:a]volume=-1[inv];[0:a][inv]amix=inputs=2:normalize=0" -c:a pcm_s24le diff.wav

The channel layout of both files must be the same for this to work.

Dan

[IoannisSyrogiannis]

You write that you exported your video project to ProRes@24fps. How is your export? Did you check that? Was the project 24fps as well?
I would check what DCP-o-matic says on your DCP-o-matic project. It usually states the duration of video, audio, as well as the framerate and the sample rate and if a change is to occur on creating the DCP.

I would first look for the culprit on different durations/framerates/sample rates. I wouldn't demux the audio from the mxf, to test as you did, I would export an mp4 out of the project. But that wouldn't tell much about the ProRes input.

Best of luck!

[neruson]

Hi,
Is the audio output device used by DCP-o-matic the same than when you play the WAV?
To make sure there is no change you can load both the master and the audio MXF from the DCP in an audio editor timeline and compare the waveforms. You can visually compare or you can invert phase of one audio and listen to the mix: if the result is silent, both audio are identical.
You can also use ffmpeg to do that with something like:

Code: Select all

ffmpeg -i "source-audio.wav" -i "dcp-audio.mxf" -filter_complex "[1:a]volume=-1[inv];[0:a][inv]amix=inputs=2:normalize=0" -c:a pcm_s24le diff.wav

The channel layout of both files must be the same for this to work.

Dan

Yes, the output device is the same when playing back in DCP-o-matic and playing back the WAV in Quicktime for example.
When I run the following I get a WAV output that sounds exactly the same as the original mp4 render:

Code: Select all

ffmpeg -i pcm_*.mxf -acodec pcm_s24le -ar 48000 dcp_audio_test.wav

I've tried this on two completely different videos and the result inside of DCP-o-matic is always the same - the preview is in sync but sounds lower in pitch and slightly slower in playback speed (resulting in the pitch drop).

The cinema has sent me video footage of their in-cinema test of the DCP and the audio pitch sounds exactly as it should, leading me to believe there is some issue with DCP-o-matic and the playback engine + my machine.

Despite knowing now that the pitch issue is not being passed into the DCP, I would still love for this to be looked into and hopefully fixed.

[IoannisSyrogiannis]

Right out of the DCP-o-matic project, or if you make a new one and add the DCP created, you may export as an MP4. With a very high quantization setting, like 39, you can make sure the video bandwidth won't be an issue.
If you haven't seen any message like "Audio will be resampled from 48000Hz to XXXXXHz" or "DCP will run at XX,X% of the content speed" on the Content>Audio and Content>Video tabs of your original DCP-o-matic project and there isn't any program running system-wide, like "audio hijack" or "loopback", the mp4 export should run O.K. on VLC or MPV or similar.
Also, on your preferences>Advanced>Video display mode, what is chosen? OpenGL? Simple?

May be that there is something on the ffprobe.log or metadata.xml that can explain the situation. Yet, without any developer able to reproduce the problem, it will be unlikely for it to be looked into.

Me, as a user, checking on a ProRes file exported from DaVinci Resolve Studio on Windows and DCP-o-matic 2.18.35 I can't see it. My Mac machine is old and stuck with Monterey. So, I can't be of much help there, I am afraid.

[Carsten]

Do you use the Macs onboard audio, or an external audio interface?

- Carsten