Is it possible to remap audio channels in supplemental DCP without recreating MXF?

Anything and everything to do with DCP-o-matic.
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Jhon
Posts: 3
Joined: Mon Feb 10, 2020 12:07 pm

Is it possible to remap audio channels in supplemental DCP without recreating MXF?

Post by Jhon »

I have a DCP where audio channels C/LFE channels were accidentally placed to Ls/Rs channels and vice verse. The DCP is already in the cinema. I can make supplemental DCP with audio-only where I will map channels correctly and recreate audio-MXF, but it will take about 7Gb for a 3-hour film.

Is it possible to make supplemental DCP which will just force DCP to remap audio channels from already existing MXF which contains those wrong channels?

Carsten
Posts: 1527
Joined: Tue Apr 15, 2014 9:11 pm
Location: Germany

Re: Is it possible to remap audio channels in supplemental DCP without recreating MXF?

Post by Carsten »

No, if you create a VF, the audio content will have to go with it. SMPTE DCPs have an option to map audio channels, but as far as I know, this mapping is also part of the audio MXF, not the CPL. Also, I don't know any tool that supports this, and server support for it is probably non-existent at this stage.

Some playout servers have options to remap audio channels in software, but few projectionists are able to create the proper setup.

Maybe supplying it in a google drive link or similar transfer method is an option.


- Carsten

Jhon
Posts: 3
Joined: Mon Feb 10, 2020 12:07 pm

Re: Is it possible to remap audio channels in supplemental DCP without recreating MXF?

Post by Jhon »

Carsten, thank you very much for such a complete answer.

Sure I can send them supplemental DCP over google drive or torrent. I just thought that it's a pitty that cinema already has content and it's just a matter of few kilobytes in MXF header which influence how does server interpret channels.

PS
I don't know the exact internal structure of the MXF file, but in theory, it's possible to compare those two MXF files containing the same audio but in different channels and to create "patch" which will change only part of the information in the wrong file to make it correct one. And in all other control files (CPL etc).

PPS
Cinema can cross switch audio cables to correct channels )

gunnar
Posts: 50
Joined: Tue Apr 15, 2014 1:06 am

Re: Is it possible to remap audio channels in supplemental DCP without recreating MXF?

Post by gunnar »

Channelmapping is not controlled by metadata. It is in fact not controlled by anything. The mapping just need to be in correct order in the MXF container.

Jhon
Posts: 3
Joined: Mon Feb 10, 2020 12:07 pm

Re: Is it possible to remap audio channels in supplemental DCP without recreating MXF?

Post by Jhon »

Just tested an idea to compare that two MXFs binary and to find the difference with jdiff.exe. I hoped that the difference will be only in a small part of the files and jdiff could find it.
No luck, the "difference" file was the same size as the original ones.
So the idea to change only a small part of the file which controls the order of the channels needs more knowledge of the internal structure of MXF.

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