Topic: 7.1 Lrs/Rrs Mapped To Incorrect Channels

In doing a number of tests, comparing the generated packages made from openDCP with Wailua (the reference standard) and with the ISDCF audio channel layout document, it is apparent that openDCP assigns the extra two channels for 7.1 to the incorrect channels.

The additional two channels for 7.1 DS are extra REAR channels, not extra front channels, as are currently mapped via openDCP. The layout is fairly strange, as there are some legacy wiring issues that needed to be considered.

The packages currently made by openDCP actually map to the older-style Sony SDDS 7.1 system, where there are additional front/center channels. These are no longer really supported, and have never been used in Digital Cinema (to my knowledge).

Creating a industry-standard 7.1 DCP would result in the following channel layout:

4. LFE/Sub
5. Left Surround Side
6. Right Surround Side
7. Hearing Impaired (Or Silence)
8. Visual Descriptive (Or Silence)
9. Silence (Formerly Center Left)
10. Silence (Formerly Center Right)
11. Left Surround Rear
12. Right Surround Rear

This presents a bit of awkwardness when creating these packages, as equal-duration silence needs to be generated to pad channels 7-10.

Other than that, the software is fantastic, and I use it regularly for many non-commercial applications. I'd be a happy donor if we could just address this one minor issue.


Re: 7.1 Lrs/Rrs Mapped To Incorrect Channels

Yes, there are some issues with audio channel mappings with digital cinema in general, complicated by the MXF Interop/SMPTE packaging. The audio channels should be correct for MXF Interop packages. There is some work to do to address the SMPTE packaging.

Re: 7.1 Lrs/Rrs Mapped To Incorrect Channels

Unfortunately, they are not correct in the way OpenDCP wraps them.

As the ISDCF document shows, if the old-style SDDS version of 7.1 were still used, which adds extra channels to the FRONT, it would be wrapping correctly. Unfortunately, 7.1 in its current state adds additional REAR channels.

Here's what you currently wrap:

1. L
2. R
3. C
4. Sub/LFE
5. Ls (5.1) / LsS (7.1)
6. Rs (5.1) / RsS (7.1)
7. HI
8. AD
9. Lc
10. Rc

11. Omitted
12. Omitted

To make properly formatted, contemporary 7.1 packages, there needs to be 12 total channels. I believe you have confused Lc/Rc for LsR/RsR.

Interop likely won't let you add channel labels, and if SMPTE does, of which there are few compliant players out there, it will require LsR/RsR and not the Lc/Rc mapping you currently use.

I'll see if I can find a 7.1 trailer and decompose its audio waveforms for you too examine.

Re: 7.1 Lrs/Rrs Mapped To Incorrect Channels

I've downloaded the Dolby Channel Identifier package and decomposed it into a readable WAV file.

If you look at the waveforms, you can see that channels 9 and 10 are silent, while 11 and 12 have "Left Rear Surround" and "Right Rear Surround" in them.

This follows the ISDCF spec for 7.1 package channel layout, as previously posted.

Package (DOLBY-71-CHANNEL-ID_TST_F_EN-XX_INT_71_2K_20110816_DLB): … 91NzQ/edit


Re: 7.1 Lrs/Rrs Mapped To Incorrect Channels

Ok, thanks for the information. I will take a look.

Re: 7.1 Lrs/Rrs Mapped To Incorrect Channels


I have created a 7.1 clip and it would not work on a 7.1 system - I mean just the back surrounds are missing. I did not investigate on the reason but it seems that what Erik says is correct.

Has that ever been addressed on the latest version?

Thanks for your efforts in creating OpenDCP!