Pictory allows the capability to choose a video resolution as well as change the aspect ratio of your video.

To find these options, navigate to the Format tab on the left side of your screen.

At the top, you can choose either 720p or 1080p video resolution, whichever is better suited for you.
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* Please note that using 1080p for your video resolution will entail a slightly longer generation time.

You also have the option Optimize the video for size. This will reduce the file size but increase the video generation time.