This is how to add black bars on your video in Premiere Pro #shorts
Letterbox Ratios:
1. 2.35:1 Cinemascope Widescreen
1080p HD: 1920 by 817 pixels
3840p UHD: 3840 by 1637 pixels
4096 C4K: 4096 by 1749 pixels
2. 2.39:1 Anamorphic Widescreen
1080p HD: 1920 by 800 pixels
3840p UHD: 3840 by 1593 pixels
4096 C4K: 4096 by 1716 pixels
3. 1.85:1 Flat Widescreen
1080p HD: 1920 by 1038 pixels
3840p UHD: 3840 by 2076 pixels
4096 C4K: 4096 by 2214 pixels
4. 2:1 Univisium Widescreen
1080p HD: 1920 by 960 pixels
3840p UHD: 3840 by 1920 pixels
4096 C4K: 4096 by 2048 pixels
5. 4:3 Fullscreen
1080p HD: 1440 by 1080 pixels
3840p UHD: 2880 by 2160 pixels
4096 C4K: 4096 by 3072 pixels