Command Line Stereo

[kufu]

Hi,

Been messing around with the command line use case of DCP-o-matic. I noticed there are maybe some limitations to the command line encoding of some DCP functionalities? Or is this just not included on the manual? I was hoping to be able to adjust the metadata to reflect a stereo dcp vs a 5.1. If I feed a file that has two channels of audio and it is going to make a DCP based off that can I define that the DCP will be a stereo DCP? Or does DCP-o-matic only do 5.1 through command line? I know the --channel functionality may have something to do with this? But to my knowledge that is just the reference to a <content> location of a audio for layback?

Furthermore, if I want to use a stereo track of audio that is multi channel can I define what channel is what in the command line when referencing a separate audio wav file?

[kufu]

Just seeing if anyone has a solution for this? Much appreciated!

[carl]

I noticed there are maybe some limitations to the command line encoding of some DCP functionalities?

It's true that right now you can do more in the GUI than in the CLI, but I'm happy to try and add missing things to the CLI. As a last resort you can write/edit the XML description programmatically, but of course that isn't so easy.

I was hoping to be able to adjust the metadata to reflect a stereo dcp vs a 5.1.

Which metadata are you hoping to adjust here?

Furthermore, if I want to use a stereo track of audio that is multi channel can I define what channel is what in the command line when referencing a separate audio wav file?

Not yet - there's a proposal to add support for that.

[kufu]

Which metadata are you hoping to adjust here?

Currently, the CLI automatically makes a 5.1 output every time splitting the stereo output into the Left and Right channels and leaving the other channels silent. Ultimately I just want a parameter that I can feed into the command line code that tells it that this will be a stereo output. I guess I haven't looked too much into this to see if I can adjust the code myself.

[carl]

So you want only the two channel to be written to the audio MXF? Current versions of DCP-o-matic won't do that under any circumstances, as we believe that certain commercial validators raise errors about audio MXFs with fewer than 8 (or possibly fewer than 16) channels. I'm looking at whether this rule should be optional or not, and if we go back in that direction we could add a channel count option to the command-line client.

[Antti N]

I'd love at least an advanced option to only write 6 (or at most 8) channels for stereo/5.1 SMPTE DCP's!

I do appreciate the effort to avoid as much validation errors as possible, on as many validators as possible… But even most studio 5.1 DCP's by far have only 6 or 8 channels, so I don't believe it's any kind of a real-world requirement to write 16 channels for SMPTE DCP's (which is the current D-o-M behaviour).

The amount of wasted space can be non-trivial particularly when you're using low j2k bitrates: with 100 Mbps video, a 16-channel DCP is 17% larger compared to a 6-channel one. I've actually used an old D-o-M version to get around this recently, when creating DCP's for internal use.

That said, writing stereo audio as a 6-track MXF (with 4 empty channels) is no problem for me personally. Much less wasted space, too, compared to always writing 16 channels.

[Carsten]

I think it s wrong to force certain channel numbers on users. This is not a formal requirement, but a workflow consideration. I think it is enough if DCP-o-matic allows to set any channel number that is assignable per spec/RDD52. We COULD issue a warning/recommendation if at all. The necessity to have a specified number of audio channels is only imposed by certain companies adding value to a DCP created with DCP-o-matic - e.g. VFs, or duplicating services.

I have analysed many commercially mastered SMPTE trailers, and the channel count of them is all over the place. 'Oppenheimer' Trailer for instance uses a 6 channel SMPTE MXF file, to name just a current one.
I understand that trailers essentially never are done OV/VF style, so, these requirements are usually put onto features. But, again, we shouldn't enforce a specific channel count just because 'some' companies demand it for their workflow's sake. It is also very easy to conform an existing DCP into a new one with an adjusted channel count if ever necessary.

[carl]

Yeah I am coming round to the idea that the enforced 16 channel thing might have been a mistake. Maybe we should make the DCP channel option work again but default it to 8 or 16 channels depending on source?

[Antti N]

Yeah I am coming round to the idea that the enforced 16 channel thing might have been a mistake. Maybe we should make the DCP channel option work again but default it to 8 or 16 channels depending on source?

Yes please

Sorry, I didn't realize that there was already a topic about this:
https://dcpomatic.com/forum/viewtopic.php?t=2121

[kufu]

Yes this would be awesome to have the option! I can see how some companies require it, but I do find myself needing to have stereo only output with only two channels of audio Lft and Rgt. Having the four blank tracks is a lot of waisted space, especially on full movies where the files sizes are much larger. Is there any work arounds yet created? I'm looking for the command line tools specifically?