How to export an AI video as a 9:16 MP4 for TikTok, Reels and Shorts

The question looks simple. You rendered six clips on an AI engine, you want them stitched into one MP4 at the vertical ratio TikTok wants, and the first ten tutorials you open tell you to use "a reframing tool". Which is right in the way that "use a hammer" is right advice when the problem is a loose nail. It is not what you actually need to know.

I run a studio where we export this specific deliverable — a 9:16 vertical MP4 of a character video — several times a day. Here is the full spec sheet for the format, the trap most AI tutorials skip, and the exact export workflow with its credit cost inside the studio.

The specs TikTok, Reels and Shorts actually accept

Every honest "export settings" post lands on the same numbers because the three platforms converged on them. These are the specs as of October 2026.

spec	value	why
aspect ratio	9:16	the only ratio that fills the phone screen with no bars
resolution	1080 x 1920	the max the apps compress against; 720 x 1280 is the minimum before quality suffers
container	MP4	universal and compressed well by every platform
video codec	H.264	the one every encoder on every phone can play
audio codec	AAC	128 to 256 kbps
frame rate	30 fps default; 24, 25 and 60 all accepted	match the source if the source is already in a sensible rate
bitrate	8 to 10 Mbps for 1080p; 4 to 6 Mbps for 720p	TikTok re-encodes to roughly 1 to 2 Mbps; a higher upload gives TikTok a cleaner input
colour	Rec.709	the standard space for the web
max file size	287.6 MB on mobile	iOS and Android cap the upload

If your export matches those nine rows, the file will play on all three platforms with no complaints. Nothing in that table is unique to AI; it is the shape of modern vertical video delivery.

The AI-specific trap

Here is what the generic export tutorials miss, and it is the whole reason AI exports go wrong.

Most AI video engines do not render at 1080 x 1920 natively. Kling and Veo render landscape or square by default. Seedance 2.5 serves 9:16 at a different pixel count. Reframing from 16:9 to 9:16 means cropping the horizontal frame — and because the character's face is usually in the horizontal middle of the frame, naive center-crop reframing is fine. Where it goes wrong is on the shots where the character moved off-center for a reason: a reaction, a two-shot, a camera that panned across them.

A center crop on a two-shot cuts one character off the edge. A center crop on a wide landscape establishes shot throws the subject matter out. An "AI reframe" that follows the speaker is a different workflow entirely and most of the time it is tracking the wrong thing — a hand, a prop, the brighter half of the frame.

The honest fix is to render at the ratio you'll ship. Every engine on our shelf serves 9:16 at a native pixel count, printed on the resolution picker before you render. Pick 9:16 at render time and you never crop a face off the edge afterwards.

The render ratio each engine serves

Our five engines, their native 9:16 output, and the resolution they land at.

engine	9:16 native resolution	notes
Kling O3 Pro	720p (720 x 1280)	the one resolution it serves; vertical by selection
Seedance 2.5	480p / 720p / 1080p (up to 1080 x 1920)	1080p costs more than double 720p; pick 720p unless you have a reason
Seedance 2.0	480p / 720p / 1080p	same shape as 2.5, cheaper per second
Seedance 2.0 Fast	480p / 720p	the draft tier; 480p is 25 credits a second
Veo 3.1 Fast	720p / 1080p	native audio, four six or eight seconds only

Pick a resolution before you render. The export does not upscale and should not: a 720p render blown to 1080p for the upload adds no information and hands the platform a less clean input.

The one-click export inside the studio

The editor exports whatever is on the timeline as one MP4. Here is what it writes.

Container. MP4.

Video. H.264 at a visually lossless CRF for the resolution of the timeline (18 for 720p, 20 for 1080p), 30 fps, Rec.709.

Audio. AAC at 192 kbps, stereo.

Aspect ratio. The timeline's ratio. If you built the timeline from 9:16 renders, you export 9:16. If you mixed ratios, the editor fits them with a safe zone around the character.

Resolution. The timeline's resolution. If every clip is 720p, the file is 720 x 1280. If any clip is 1080p, the file is 1080 x 1920.

Credits. Twenty, flat, whatever the timeline is. The export is free from the Creator plan up.

The reason an export is twenty credits — the same as a character sheet — is that there is no third-party provider behind this one. The stitch runs on our own ffmpeg; the cost is a few minutes of a container we are already paying for. A per-second rate on a free-to-us operation would be dishonest; a flat price at the sheet cost is cheap enough that nobody has to think about whether re-cutting a reel is worth the credits.

The workflow, start to finish

Here is how I actually do it, from six raw renders to one MP4.

1. Pick 9:16 at render time. Before the first clip, open the picker, set the aspect ratio to vertical, set the resolution to 720p unless the client needs 1080p. Every clip inherits the ratio.

2. Render clip by clip into one project. Six clips, five to fifteen seconds each, same character, same reference sheet, same identity prompt. The project is the editor's timeline — not a separate "import" step. Clips land on the timeline when the render completes.

3. Trim and reorder on the timeline. The clip handles are three seconds either side of the asked length so a 12-second render has 18 seconds of material to pick from. Pick the first second of your clip; trim the last second if the character looks away.

4. Audio pass. If every clip has native audio from the engine, this is a mix pass: level the dialogue, duck the music under speech, add a bed if nothing is under the dialogue. If some clips were silent and others voiced, the editor can lay a voice line or music under the silent beats without a re-render.

5. Caption pass. The editor transcribes the audio and writes burned-in captions, 90% safe-zone off every edge. Captions cost eight credits a started minute of audio on free and Lite, free on Creator and up.

6. Export. One click. Twenty credits. The MP4 lands in Downloads at 1080 x 1920 (or 720 x 1280 if that is what the timeline is) with the specs in the table above.

7. Upload. TikTok, Reels and Shorts all accept the file as written. The first time you upload one, verify in each app that the preview is edge-to-edge with no bars; if any bars appear, the ratio in the file does not match 9:16 and the export was from a mixed-ratio timeline.

The specific traps I see

Three failures I see on exports that should have worked.

The timeline is a mixed ratio and the export letterboxed. A 16:9 clip pasted onto a 9:16 timeline is a letterboxed clip. The fix is to render that clip again at 9:16 — or, if you cannot, reframe it in the editor with the subject in the safe zone before export.

The caption safe zone is wrong. Captions written for a landscape timeline sit too wide on vertical and get clipped by the platform's own overlays (the username band at the bottom of TikTok, the comment column on Reels). The editor's default safe zone is 90% off top, bottom, left and right, which clears every overlay I have seen; if you edited the safe zone, reset it.

The upload is a 2 GB export of a 90-second clip. Somewhere the bitrate ran away. Mobile uploads cap at 287.6 MB. Our export caps the bitrate at 10 Mbps for 1080p by design; if you exported from a different tool, cap the bitrate yourself.

The honest part

Our 9.7 million views across thirty days on @cevrico shipped as 9:16 vertical MP4s to TikTok, Instagram Reels and YouTube Shorts, from the same editor the studio exports from today. Our own results, not a projection; yours will depend on what you make.

A free account comes with 300 credits: a character sheet, a four-second voiced test on Kling or Veo, and the first export of your first clip, before you spend a dollar. The twenty credits an export costs are the cheapest step in the workflow and the one the whole thing is for.