Bizarre 5.1 audio issue

[worldofcrap]

Howdy folks!

We use DCP-o-matic on a near-daily basis for making trailer DCPs. However, this one totally threw us. We have a trailer ProRes file that is in a pretty standard audio configuration: 5.1 in L/R/C/LFE/Ls/Rs, plus stereo. However, when we do our usual channel configurations and output to DCP with DCP-o-matic, the resulting MXF has 16 CHANNELS! 10 of them are silent.

Here's where things get wacky. We've tried exporting the audio as a multichannel WAV, and then adding it as a separate element. We've tried encoding it to SMPTE MXF in another program and rewrapping with DCP-o-matic. We've tried re-encoding the ProRes file with ONLY the 5.1 audio. No matter what we do, DCP-o-matic spits out an audio MXF with 16 channels.

Any clue what might be going on here? We've tried this on multiple machines, both Win and Mac. I'm currently running v2.16.55.

Thank you!

[carl]

Hi

This is a deliberate change (which itself might need some adjustment!) We are finding that certain distributor "QC" processes are raising errors with SMPTE DCPs that don't have the full 16 channels of audio (even if many of them are silent). I decided to make DCP-o-matic always produce 16 channel audio MXFs in SMPTE mode.

This is wasteful, of course, but has a reasonably small effect compared to the size of the video MXF in most cases, and it shouldn't cause any problems on playback.

It may be that we can get away with only writing 8 channels for 5.1 DCPs, or that we need to add an option to disable this feature. But for now, it's expected. If it causes you any "real" problems (i.e. problems on playback) do let me know!

Best,
Carl

[Carsten]

I think we should not enforce this full channel layout on users/SMPTE DCPs in general. We could simply use an additional name/description for the 16ch layout, and let the user decide to select it. A regular hint towards this could be given in the regular hints dialog.

[worldofcrap]

Thanks so much for the clarification. Of all the dumb hoops these companies make us jump through, this has to be one of the silliest.
I do hope at some point there’s a way to turn this off when it’s totally extraneous, but… ah well.

[carl]

I think we should not enforce this full channel layout on users/SMPTE DCPs in general. We could simply use an additional name/description for the 16ch layout, and let the user decide to select it. A regular hint towards this could be given in the regular hints dialog.

I think ideally though if users select 16-channel we also want to know how many "active" channels they have so we can write the correct metadata. I guess we could get this from the channels that are mapped.