Audio in DCP-o-matic Player

[marcelmax]

Hi,

when I playback a 5.1 DCP in DCP-o-matic Player I wonder which channels I hear on my stereo MacBook?
Is it a mix?
I've created such a DCP and it sounds like there is no Center, when I play back.

Thanks!

[Carsten]

It's a stereo downmix for a standard stereo audio playback device, however, your currently configured audio device may offer more than two channels, and so DCP-o-matic may render the center channel to a different channel, and not necessarily to one that is immediately audible.
DCP-o-matic is able to play multichannel audio to multiple discrete output channels, if the chosen audio devices offers that number of channels. I tried this through HDMI, and was able to play 7.1 sound to a 8ch playback device.
I don't know how exactly DCP-o-matic decides about how/when to downmix. It's pretty obvious for two playback channels, but what if you e.g. play a 5.1 mix to four channels? Maybe Carl can comment. I would assume it should only do a full downmix for a stereo playback device, and map channels 1:1 for any higher playback channel count, even if that means that some audio on higher track numbers would be left unheard. Because it is pretty normal to do L/C/R mixes to 4 channels. Of course, in DCP-o-matic main application, you can map channels freely.


It should work for you, however, as I just played a commercial DCP trailer (Star Wars 8) with Player 2.12.2 on my Mac Book Pro in Sierra trough the onboard stereo sound system - center channel with dialog is clearly there. Maybe check your OS X audio configuration, and the device chosen in DCP-o-matic prefs?

You can also test it with DCP-o-matic main application - load your DCP into a new project, play it, check by activating/deactivating the channels in the matrix. Maybe your DCP has the wrong channel mapping?

- Carsten

[carl]

I don't know how exactly DCP-o-matic decides about how/when to downmix

It's not very intelligent at the moment. If there is stereo output and a DCP with at least 3 channels it bounces L and R down to C. Otherwise it plays L on channel 1, R on channel 2, C on channel 3 and so on until it runs out of channels.

We probably need a better system here. It's possible that in some cases DoM gets the sound card channel count wrong...

[Carsten]

I think it is not so bad the way it is. I talked to some people who are creating 5.1 DCPs, but really only L/C/R mixes, and use 4 channel output hardware. Without any complicated additional monitoring hardware mapping setup, downmixing all active channels to stereo devices, and doing a 1:1 mapping as far as output channels above 2 go, is practical. If any mapping is needed for special applications, I guess users could do that in the matrix, even if that actually changes the DCP channel mapping. It may get nasty if you have many audio files in a project all in individual mono files, e.g. reel segmented, because you would need to adjust all their mapping just for the monitoring. The only solution would be to set up another monitoring channel mapping matrix in prefs. But that would really make things complicated to understand and control, especially since the OS will likely have a similar setup (OS X and windows have it). Again, I think, for now, it's okay the way it is now.

Since FreeDCP is gone forever, maybe we could setup some demo files to help people in analyzing these things. Like in this case, a channel count DCP.

Needs quite some hosting space and traffic allowance, though.

- Carsten

[carl]

Since FreeDCP is gone forever, maybe we could setup some demo files to help people in analyzing these things. Like in this case, a channel count DCP.

That might be useful. I'm on digitalocean and they offer 250Gb with 1Tb of outgoing bandwidth for $5 a month, some of which I'm currently using to host old DCP-o-matic downloads. Maybe that would be OK as a starting point. I can imagine the outgoing bandwidth getting quite silly quite quickly though.

[Carsten]

Yes, one should be very careful with the size of the files put up there. Some static image DCPs compress very nicely with some packers (not ZIP, though).

I always wanted to put up an organized set of test files on a free google drive account. It's 'only' 15 GB, but that is already something for a specific set of test files. And I think Google doesn't care about the traffic from these?
I also thought that a set of those files could help in analyzing potential bugs. Just as we sometimes refer to the benchmark videos for testing.

- Carsten

[carl]

I think it's a good idea. Maybe we can try digitalocean and try to think again if it starts costing serious money.