Best Practices for aspect ratio handling for converting a Blu Ray 16x9 movie into a DCP

[Squidmaster7]

Hi everyone, I am planning on screening a film in a cinema very soon. To do this ill need to turn the MKV(from bluray) I have into a DCP. Ive tried to read around the forum and watch some youtube videos to learn some. I still have some questions though.
Heres the details:
The movie is 1920x1080 and is 2.35:1 (or 2.39) not sure.
The audio is DTS-HD 5.1.
The theater has a 2k projector, I didnt ask about aspect ratio but my 99% assumption is that its 1.85 like most theaters.

My main question revolves around aspect ratio. What are the correct scale and crop settings in DOM? Any help with this would be greatly appreciated. I know that in the theater there will obviously be some letterboxing considering it is a 2.35 movie.

The workflow I saw in a youtube video was to set the container to Scope, scale the content to Scope (this option seems to be missing or moved in the beta release), and then crop the top and bottom (by 140 and 138). The issue is, the UI is different in the new beta release and I cant replicate this.

[Carsten]

The current beta is very different around the scaling options. I guess I am personally responsible for this change, but I did not have the time to play with the new scheme so far.

You may just as well use the latest release version - anyway recommended for production work, 2.15.x has a lot of fundamental changes.

You can measure out your content pixelwise to see the actual aspect ratio/pixel count. This will also help with precise cropping.
I usually take a snapshot in VLC of a frame which has bright signal on all four edges. Then I load the image into an image editor and measure out the black bars. But that is for those of us who want it to be extra precise.

You can also crop visually in the preview window - better if you work on a highres screen, not a tiny laptop screen, so you catch single pixel rows more precisely. Configure a scope container, just use 'No-Stretch', then crop away all black bars. That is now the most simple way to keep the original aspect ratio and prevent any unnecessary scaling.
This will result in a standard scope DCP that every cinema is able to play.

- Carsten

[Squidmaster7]

Thanks for your reply Carsten. Heres what I did:
1. Imported the MKV into DOM
2. Set the Container to DCI Scope
3. Set the Scale to No Stretch
4. Cropped 138 from Top and Bottom. This looks right to me.

DOM says "cropped to 1920x804 (2.39:1). Visually everything looks good to me in the preview window, I dont see any black bars, stretching, or anything missing.

Screen Shot 2020-06-24 at 8.23.21 AM.png

Would you mind taking a quick look at the screenshot I provided of the settings?
Once again, thanks for your hard work and dedication creating this program.

[Carsten]

Looks good. If you are absolutely mad about scaling, you could leave out all scaling by choosing 'no scale', and then just crop away the same amount of vertical pixels. That would place a 1920/804 active image within a 2048/858 scope container. That would mean letter AND some pillarboxing, which may be okay on an unmasked flat screen. But I would only do that if the content would be extremely critical detailwise and if you can check the screen layout before.

Check volume/loudness. Activate the full audio analysis ('LUFS'), and try to hit a LUFS value around -20 (add positive or negative gain to the audio track as necessary). You could also post a screenshot here.



- Carsten

[Squidmaster7]

Thanks for the confirmation. It isnt absolutely necessary that its PERFECT. Pretty good is A-Ok. I have other minor question: I have another copy of this file but it is in 3840x2160 10bit (not HDR though, still REC. 709) instead of 1920x1080 8bit like above. Just for a test, I imported the 2160p copy into DOM, set container to DCI Scope 2k (not 4k), and cropped off the top and bottom (I think it was like 270 instead of 138 for the 1080p copy). My theory is that by using the 4k source file I am effectively downsampling and getting and higher quality image due to the greater amount of pixels and bit depth. Does this sound correct to you? It looks fine in the built-in editor.

Regarding audio: I did perform a check and I think it came out to something like -22 LUFS. I saw another thread on here regarding DTS-HD MSTR and how in MediaInfo the Channel Layout was C,L,R,LFE, etc instead of the regular L,R,C,LFE, etc. I checked and ran into this as well. When I put the DTS track into Audacity though it appears to be correctly laid out. I guess its just a weird quirk. I ended up converting the DTS-HD MSTR track into separate WAV tracks. I did this because I figured DOM was only using the DTS-core and not the whole DTS-HD track (though maybe I'm wrong). I'm only going to get one shot to project the film correctly so I want to make sure the channel mapping is perfect since I wont have a chance to test before hand.

[Carsten]

The channel order should be correct for DTS-HD. When I grab a DTS-HD track, typically the standard dts core is included, and I can select in DCP-o-matic which of the two 6ch streams to use.

- Carsten

[Squidmaster7]

For this specific file the Audio content tab is only showing one track (it says DCA) but I know its a DTS-HD track. It decodes as such on my home theater receiver. I went ahead and converted it to WAV just to be safe on my side. Do you have any thoughts on the downsampling idea I posted above? I promise this is the last of my questions

[Carsten]

If you have an UHD source file, and you see that e.g. the color conversion is correct (some color spaces could be a problem), yes, the UHD source will probably give a slightly better result. I am not sure if DCP-o-matic correctly deals with the 10bit color depth, but, DCP uses 12bit full range, and standard BD/rec.709 8Bit limited range, so, at least in theory, the UHD source should be more adequate for a DCP conversion. It would be quite interesting to do both and then compare in a cinema.

You could do a real 4k DCP as well (it is compatible with 2k projectors, the projector will only play the 2k component of it), but it will probably take four times as long to render.


- Carsten

[Squidmaster7]

I went ahead and created the DCP with the UHD file. It seems fine. It plays in DCP-o-Matic Plater. Just for fun I tried the Verify feature and it returned these two errors which I assume are the video and sound files.

"The hash of the picture asset j2c_b7505d63-db33-4895-8f5d-d50b8d3ef2a2.mxf does not agree with the PKL file. This probably means that the asset file is corrupt."

"The hash of the sound asset pcm_fb875466-71b5-4a72-bc0c-ef0342567102.mxf does not agree with the PKL file. This probably means that the asset file is corrupt."

I have skimmed around the video in DCP Player and it 'seems' fine. Is thias something I should be concerned about? Im assuming some sort of checksum came back incorrectly.

[Carsten]

Hmm...which version of DCP-o-matic did you use? On what disc (internal, USB, format) did you create this DCP? I think this IS serious. I would redo the DCP, make sure the MXFs are actually recreated.

- Carsten