Learning how to make a vertical video for TikTok and Reels is mostly about two things: composing for a 9:16 frame from the start and exporting a file that plays instantly. Get those right and your content looks native to the feed instead of like a landscape video awkwardly cropped to fit. This guide walks through directing a 9:16 cut with AI and exporting a faststart MP4 through the CoreReflex render path so it begins playing the moment it loads.
Why 9:16 is the format for TikTok and Reels
TikTok, Instagram Reels, and YouTube Shorts are all built around a full-screen vertical canvas. A 9:16 frame fills the entire phone screen, which means more pixels devoted to your content and zero black bars stealing attention. Vertical video also matches how people actually hold their phones, so it feels effortless to watch.
The practical implications are real: a video shot for 16:9 and cropped to vertical loses the edges of every frame, often cutting off faces, products, or text. Composing for 9:16 from the first shot avoids that entirely. If you also publish to other placements, our companion guides on the square video format for Instagram and LinkedIn video ads cover how the same film adapts to different feeds.
How to make a vertical video for TikTok and Reels
Here is the end-to-end workflow in CoreReflex, from a sentence to a feed-ready file:
- Describe the video in one sentence. Tell the agentic Director what you want, the subject, the vibe, and the platform. The Director runs a PLAN → PRODUCE → CRITIQUE → ASSEMBLE loop and boards your shots before generating anything, and planning is free.
- Set the aspect ratio to 9:16. Lock vertical at the start so every shot is composed for the full-screen frame rather than cropped after the fact.
- Board the shots and refine camera moves. Each shot carries a role, a camera move, and a prompt. Vertical thrives on motion that respects the tall frame, push-ins, tilts, and reveals. For ideas, our guide to prompting motion and action in video shows how to direct movement that reads well on a phone.
- Keep the subject and text in the safe zone. Platform UI, captions, usernames, buttons, overlays the top and bottom of the frame. Keep critical action and copy in the center band so nothing important gets covered.
- Run the quality gate. Every shot is scored on prompt match, sharpness, motion coherence, and on-screen text legibility, and any shot that fails is selectively regenerated. Legible text matters more in vertical, where viewers are close to small type.
- Add captions for sound-off viewing. Most feed playback starts muted, so captions aren't optional. See how to add captions to a video with AI and, for more energy, how to add animated captions.
- Export a faststart MP4. Render through the deterministic render path to get a vertical file optimized to begin playing immediately.
Design for sound-off and the caption safe zone
Vertical video is watched thumb-on-screen, often muted, often in a noisy environment. Two design rules follow from that.
First, assume no audio. Your hook has to land visually in the first second, and your message has to be readable without sound. Captions carry the narration; motion carries the attention.
Second, respect the safe zone. TikTok and Reels layer their interface over the edges of the 9:16 frame, the caption, the handle, the like and share rail, and the bottom navigation. Anything you place too close to an edge risks being obscured. Keep faces, products, and on-screen copy within the central portion of the frame, and treat the outer margins as decorative space only.
Export settings that matter for TikTok and Reels
The difference between a video that feels snappy and one that feels sluggish often comes down to the file itself. CoreReflex renders through a real render-worker pipeline, claim job, render, upload to your storage, asset row, with retries, a dead-letter queue, encoder tiers, and faststart enabled.
Faststart matters specifically for social. It moves the file's metadata (the "moov atom") to the front of the MP4 so a player can begin streaming before the whole file downloads. On a feed where a half-second of buffering means a scroll-past, that head start is the difference between a view and a miss. And because the render path is deterministic, the same manifest always produces the same cut, so when you re-export or make a small change, you get a predictable, repeatable result instead of a surprise. For the technical detail on encoder tiers and the queue, see the product documentation.
A few format reminders for the vertical feed:
- Aspect ratio: 9:16, set before you board shots, not cropped after.
- Captions: burned in or added in-platform, since most playback is muted.
- Hook: visual and immediate, earn the first second.
- File: a faststart MP4 so playback begins instantly.
This same vertical workflow scales across industries, our breakdown of 4K hotel property showcases shows how the same render path handles a very different brief. Browse more tutorials on the AI video hub.
Frequently asked questions
What aspect ratio is best for TikTok and Reels?
9:16 vertical. It fills the entire phone screen, matches how people hold their devices, and avoids the black bars or cropped edges you get from forcing a landscape video into a vertical feed. Compose for 9:16 from the first shot rather than cropping at the end.
Can I export a faststart MP4 for fast playback?
Yes. CoreReflex renders through a deterministic pipeline with faststart enabled, which moves the file's metadata to the front of the MP4 so players can begin streaming immediately. On TikTok and Reels, where a moment of buffering loses the viewer, that instant start helps your video hold attention.
Can I reframe a landscape video to 9:16?
You can, but composing in 9:16 from the start gives a far better result. Cropping a 16:9 video to vertical discards the edges of every frame and often cuts off faces, products, or text. In CoreReflex, you set vertical before the Director boards shots, so each one is framed for the full vertical canvas.
Direct your first vertical video
Making vertical video for TikTok and Reels comes down to composing for the tall frame, designing for sound-off, and exporting a file that plays the instant it loads. With an agentic Director boarding 9:16 shots and a render path that ships a faststart MP4, you can go from a sentence to a feed-ready cut without ever touching a manual crop.
Ready to publish something that looks native to the feed? Start free with no credit card and direct your first vertical cut.