This method uses NDI and OBS as a bridge between Premiere Pro.

The problem

Background

With a non-standard sequence resolution like 1080 x 1080 (1:1) or 900 x 1080 (5:6), Premiere will attempt to output exactly that resolution to the Blackmagic Decklick or UltraStudio Monitor device.

However, Blackmagic's monitoring devices are SMPTE-compliant and only output standard formats like e.g. 1080p25 (1920 x 1080).

In these instances, Premiere permits you to output nothing from your Blackmagic monitoring device or to 'Scale up' or 'Scale down' either the width or the height to conform to an appropriate resolution.

However, neither setting preserves the correct aspect ratio of the image and instead distorts it.

For example, a 4:3 timeline (1440 x 1080), the result with 'Scale up' is that the 4:3 image is horizontally stretched to 16:9, which is obviously unusable.

There is no option (as far as I found) within Premiere to pillarbox or letterbox the sequence in order to preserve the custom sequence's aspect ratio within the bounds of a standard format.

Method

In this guide, the Premiere sequence is output to NDI, which supports arbitrary sizes of video streams.

OBS is then used to receive the NDI stream, size it appropriately on a canvas of 1080p or other acceptable resolution, and then output that to the Blackmagic monitoring device.

Finally, the 'total travel time' of the video signal from its origin in Premiere to its destination on the physical playback monitor is measured using a timecode display and a slow-mo phone recording.

The NDI stream does not leave the computer and everything takes place 'in-the-box' at the application level.

This does mean that additional computing power is required (i.e. OBS) which does add latency.

However, in film/TV applications, some kind of latency for playback devices is expected and Premiere permits an offset in miliseconds to be specified to ensure synchronised playback.

The guide

Requisites

• Blackmagic Decklink or UltraStudio device.
• Blackmagic Desktop Video Setup app (from Blackmagic Support website).

This guide's assumptions

Assuming macOS 10.15.7, an UltraStudio Monitor 3G device, a working framerate of 25 FPS and a physical display monitor that is capable of accepting a 1920 x 1080 video signal (but ergo, not capable of non-standard sizes like that of your Premiere sequence).

In my case, the custom sequence resolution is 4:3 1080p (1440 x 1080) and the physical display monitor is connected to the UltraStudio Monitor 3G over SDI.

Steps

1. Download these:
   1. NDI Tools – (https://ndi.tv/tools/#download-tools)
   2. OBS – (https://obsproject.com)
   3. OBS plugin 'obs-ndi' by Palakis – (https://github.com/Palakis/obs-ndi/releases/download/4.9.1/obs-ndi-4.9.0-macOS.pkg)
   4. NDI runtime – (https://ndi.palakis.fr/runtime/ndi-runtime-4.5.1-macOS.pkg)
2. Run the installers in the above order.
3. After installation, restart your OS.
4. Configure Premiere Pro:
   1. Launch Premiere Pro and enter Preferences > Playback, enable NDI output.
5. Configure OBS:
   1. Launch OBS; add a new Source (+) as "NDI(TM) Source".
   2. In Preferences -> "Video", set:
      • Both the Base Canvas Resolution and Output Scaled Resolution to 1920 x 1080. This should be a resolution that your display monitor is capable of handling.
      • Common FPS Values: 25 PAL
   3. In OBS menu bar -> select "Tools" -> "Decklink Output".
   4. For Output, select "UltraStudio Monitor 3G" or your device from the Device dropdown.
   5. Set the Mode to 1080p25.
   6. Check [x] Auto start on launch.
   7. Press 'Start', to begin outputting to your decklink now, and close this Decklink Output window.
   8. Add a new Source (+) as "NDI(TM) Source".
   9. In the Preview window, right-click the Source's red rectangle and choose "Transform" -> "Fit to Screen".
   10. Also, choose "Transform" -> "Centre to screen" to place it dead centre.
6. Measure the total travel time between Premiere Pro and your physical playback monitor:
   1. On your custom sequence, ensure there is some kind of video.
   2. Add a "Timecode" effect with size set to something large (~75%) and Time Display set to 25. This will allow you to measure the delay required for the NDI output, in the final step of this guide.
   3. Using a smartphone with slo-mo recording, film from an angle where you can see both Premiere on your computer AND your physical playback monitor.
   4. Play back the sequence in Premiere and ensure that the text size of the Timecode is large enough to be seen on both displays.
   5. Watch the recording and observe the difference in Timecode between the computer and the physical playback monitor.
   6. In my case, the difference was approximately (but not perfectly) 5 frames -- at the same moment of time in the world, the computer showed 00:00:01:06 and the physical playback monitor showed 00:00:01:01.
   7. Calculate the frame difference in miliseconds (ms): 5 frames = 5 / 25 = 0.2 sec = 200 ms.
7. Configure Premiere Pro again:
   1. In Preferences > "Playback", set the "Offset" for NDI Output to 200ms.
   2. Play your sequence once more. You should observe that playback is now approximately in sync between your two displays.

Now each time you edit

You must simply:

• Run OBS in the background.
• Not have any other program actively using your Decklink or UltraStudio device already (like DaVinci Resolve), which could stop OBS from using it.

But no other actions from you are required – OBS should just immediately start outputting your sequence to SDI and voila.

Premiere will remember your NDI output choice and Offset setting.

OBS will maintain the last scene the way it was left, with the NDI Source we added, and it will output to Decklink on startup (as we also configured this).

Sebastian Reategui 01/04/2022