OBS issues when capturing two screens

Question

I'm using OBS v25.0.8 for Mac and I'm trying to capture a two screen video, one from my laptop camera (Facetime camera 1280x720) and one presentation (Window share PowerPoint).

I set up my video config as follows:

• Canvas 3840x1080
• Output 1280x720 (OBS set this automatically)

As you can see from the screenshot above, the PowerPoint presentation is not taking the full width, leaving an empty space between the two screens.

I tried changing the output ratio, but nothing seems to happen. My laptop is a Macbook Pro with the following display 15.4-inch (2880 × 1800)

What is the correct calculation to get the two screens to fit proportionally?

Answer 1

You could eliminate the gap by reducing the width of the Base Resolution from 3840 to what fits: 1280 + the width of the powerpoint presentation. You may need to drag the righthand frame over, but it should fit.

But you've got another issue: your Base and Output are very different aspect ratios, so your output will be distorted as it smushes 50% horizontally (to use a technical term :-).

If you're going to output (capture) 16:9, I believe your canvas needs to be at that ratio too. If you keep the base height 1080, the base width should be 1280 / 720 * 1080 = 1920.

To handle that, you can start by cropping your Facetime camera on the sides, although it won't be enough. You'll need a different aspect ratio in your PowerPoint itself, which will likely require changing the layout of all your slides. Alternately, you could shrink down the presentation in OBS, leaving a gap above and below it and have a nice background color behind the whole frame (or some cool looping animation).