Fixing A/V sync of single reel DCPs with a small VF

[chr.hove]

From time to time I encounter DCPs with audio and video out of sync.
Currently I am making a VF referencing only the video content and generating a new audio MXF.
For ease of distribution, it would however be nice if I was allowed to fix the A/V sync by referencing the audio file as well and adjusting the delay in the content audio tab.
That way the VF would only contain references to the original video and audio files, and only a new XML structure would have to be distributed.
I imagine that this could be accomplished by changing the <EntryPoint> and <Duration> of the reel specification in the CPL.
This would limit the granularity of the delay to numbers of whole frames, but I guess that this is sufficient.
I am aware that this trick probably only would be applicable to single reel DCP's to avoid loosing audio or video at reel transitions.
So is there a way to make DCP-o-matic (GUI or CLI) generate a new set of XML's referencing the original video and audio MXFs and adjust the entry point and duration specified in the CPL?
Cheers,
Christian

[IoannisSyrogiannis]

In short, no.

There is no entry point configuration of audio or video (subtitles don't have that feature by default) with DCP-o-matic.
It's something that has been discussed in the past. The reasoning behind having that feature is generally acknowledged, yet, implementing it would ask for great changes on the way the program works and it's not currently something set on the updates timeline. (At least, as far as I know.)
That, is a bit of a problem for such handy fixes.
Yet, for the specific task you are looking for, there might be ways. I have to check what happens when you import as a DCP and use "split by content".
Or, what if you remove equally from one side of an essence as from the other side of the other (essence). Essences being the video, audio, etc.

[carl]

There are a few tricky things here, but I think the main problem is if you have a single-reel film with say N frames, and you want to shift the sound by 1 frame, you end up with a N-1 length sound asset. So you'd have to also trim a frame off the end of the picture to keep each part of the reel the same length. Maybe that's not such a big deal.

[chr.hove]

Okay, I just made a simple test:
- Made a copy of the out-of-sync DCP, modifying the CPL <EntryPoint> and <Duration> of the video (audio was early) and changing <Duration> of the audio to match the video.
- Created a project in DOM and added the modified DCP, referencing both video and audio (checking "Use the DCP's..." in audio and video tab)
- Generated the VF DCP
- Ingested it in one of our screens.
It seems to work
I guess that DOM does not hash check the CPL against the PKL when adding it to a project - to my luck

[chr.hove]

Wolfgang Woehl's dcp_inspect on the other hand does not like the generated VF at all:
Error: CPL 47e5c9c6-5ec6-4bd1-9eaf-b19aeed7f5b9: Found inconsistent image DecompositionLevels values across the composition (). This will produce visual artefacts in reel transitions
Error: CPL 47e5c9c6-5ec6-4bd1-9eaf-b19aeed7f5b9: Found inconsistent sound ChannelFormat values across the composition (). Playback will fail completely