Your screen is 16:9 and TikTok wants 9:16. Four ways to handle that, which one looks least bad, and the export settings each platform actually wants.
The problem with posting a screen timelapse to TikTok is geometric. Your monitor is 16:9 and the platform wants 9:16 — not just a different size, the exact opposite shape.
There's no setting that fixes this. Something has to give, and the four options each cost you something different.
Option 1: crop into the screen
Take a 9:16 slice out of the middle of your 16:9 recording and throw the rest away.
Looks: best of the four, when it works. Full bleed, no bars, native to the platform.
Costs you: about two thirds of your screen. Fine if the interesting part of the work stays in one column — a code editor, a phone-shaped design, a document. Useless if you're moving between windows across a wide monitor.
Trick that makes this work: before you record, resize the window you care about to roughly a third of your screen width and put it in the centre. Then the crop is decided at record time and you keep the resolution.
Option 2: record a portrait-shaped region
Rather than cropping afterwards, only record the region you want.
Most screen recorders let you pick a window or a region rather than the whole display. Set that region to 9:16 and every frame is already the right shape at full resolution — no crop, no scaling, no lost pixels.
This is the one I'd recommend if you know in advance that the output is going vertical. It's the same amount of work and the result is sharper, because nothing gets thrown away.
Option 3: letterbox with a background
Put the full 16:9 recording in the middle of a 9:16 frame and fill the space above and below.
Looks: fine, if the fill is deliberate. A flat colour matching your brand, a blurred copy of the video, or a title above and a caption below all work. What looks lazy is plain black bars.
Costs you: the video occupies maybe a third of the screen height, so anything small on screen becomes unreadable on a phone. If you're showing code, this is usually the wrong choice.
Best used for: short clips where the shape of the work reads at a glance and detail doesn't matter.
Option 4: stack two sources
The format that does well for process content: your screen filling the top portion and a camera of you filling the bottom, or the reverse.
Both sources are cropped, but each is cropped to a shape that suits it, and the vertical frame is fully used. This is why so many "build with me" and "study with me" videos look like this — it's the only layout that puts a wide screen and a person in a tall frame without wasting space.
Recording both sources at once is the part that needs a tool built for it. Tau does screen and camera simultaneously into one timelapse, so the two are already in sync rather than needing to be aligned afterwards.
Export settings by platform
The specs converge more than people expect, but the details differ:
| TikTok | Reels | Shorts | |
|---|---|---|---|
| Aspect | 9:16 | 9:16 | 9:16 |
| Resolution | 1080×1920 | 1080×1920 | 1080×1920 |
| Frame rate | 30 | 30 | 30 or 60 |
| Max length | 10 min | 90 s | 3 min |
| Format | MP4 (H.264) | MP4 (H.264) | MP4 (H.264) |
A few things worth knowing beyond the table:
Everything gets re-encoded. Whatever you upload, the platform compresses it again. There's no point exporting a 200MB file — it will be crushed regardless. Export at a good bitrate at 1080×1920 and stop there.
Don't upload above 1080p vertical. 4K vertical gets downscaled and often looks worse than a clean 1080 export, because you've given the encoder more to throw away.
Keep text large. Whatever you think is readable on your monitor, halve the screen area it occupies and check again. A lot of screen-recorded content fails purely because the code was 12pt.
Safe zones matter. All three platforms overlay UI on the bottom third and the right edge — captions, buttons, usernames. Keep anything important out of roughly the bottom 20% and the right 15%, or it sits under a share button.
Which to pick
If you're deciding quickly:
- Showing one window's worth of work → option 2, record a portrait region.
- Showing yourself and your screen → option 4, stack them.
- You already have a 16:9 recording and can't redo it → option 1 if the action stays central, option 3 if it doesn't.
- The detail matters more than the format → post it horizontally on YouTube instead, and don't fight the aspect ratio. Covered in how to create a timelapse for YouTube.
The general lesson, which took me longer to learn than it should have: decide the output shape before you record, not after. Every option above is cheaper and looks better when the decision happens at capture time.