How to Fake a Cinematic Aspect Ratio in Premiere
You may have noticed that it is super popular lately to use wider aspect ratios that simulate a cinematic look. The standard aspect ratios for film and tv are 4:3 (standard) and 16:9 (widescreen) which are aspects of 1.333 and 1.777 respectively. Some popular cinematic aspect ratios are 1.85 (theatrical) and 2.39 (anamorphic theatrical) which are longer and thinner. If you want to be legit, you can get this effect by desqueezing anamorphic footage.
Most of us don’t have the time and money it takes to do that well, but you can still mimic that cinematic aspect ratio by adding black bars to the top and bottom of your footage and just letting the middle part through. Here's how:
For my math I am going to assume 1080x1920 footage but the equation I am about to give you will work with any footage and desired aspect ratio. The basic equation to figure out the size of the bars that you want is (Original Height - Original Width/Desired Aspect Ratio)/2. So if you wanted to take 1080 footage and make it into the 2.39 aspect ratio, you would do (1080 - 1920/2.39)/2, which is about 138. If you add a bar of that height at the top and the bottom of your footage, you’ll end up with 1920 pixels on the x-axis and 804 pixels on the y-axis. If you divide 1920 by 804, you get 2.388, which is as close as you can get to 2.39 with 1080 footage.
There are a couple of ways to actually add the bars over the footage. the simplest is to just do it in Premiere with a title, but I prefer to do it with Illustrator files because they are reusable and still editable if you need to tweak something.
How to do it with a legacy title
You can do it with a legacy title in Premiere. It doesn’t take too long once you know the sizes you want. Make a new title, add a shape, set the width to 1920 and the height to 138. Option+Click and drag to duplicate. Center on the vertical axis. Set the heights. Drop that title on top of your footage.
How to do it in Illustrator file
I like to do it in Illustrator so that once I've made one once, I can just import it into any video where I want to use it. Start with the template for the size of video you are delivering. Make a rectangle of the desired dimensions (here 1920 by 138). Option+click and drag to duplicate. Align them with the edge guides. It should snap unless you have that turned off. Save the illustrator file as something memorable like 2.39 Aspect Black Bars for 1080 in a place where you keep reusable files. Then anytime you need it you can pull that illustrator file into your Premiere project and just drop it on top of your footage.
How to do it with a nested sequence
You can also do something similar with a nested sequence. Make a new sequence and set the width to 1920 and the height to 804. Build your sequence here and you can export it at this resolution if you want the aspect ratio without the black bars burned in. If you want to burn the black bars into it, you can make a 1080 x 1920 sequence and just pull this whole sequence into it. This method has the advantage of being able to export the video with or without the black bars, but it makes it a little harder to edit. (You can set the opacity of the black bars lower on the other methods, which allows you to see all the footage and get your framing right.)