How to Make an AI Video from Text and Write Prompts for Short Social Clips

October 5, 2026 · 4 min read

A text-to-video generator takes a written description of a scene and renders a short clip from it. On SentX, the flow is straightforward: describe the scene or upload a still image, pick an aspect ratio, generate, preview the result in the browser, adjust the wording or starting image, regenerate until the motion and look feel right, then download. That loop is where the work happens.

The part that separates a usable clip from a wasted generation is the prompt. For short social content, plan each generation as a single shot: one moment, not a full narrative.

Writing a prompt for a single short clip

The structure below is adapted from Runway's Gen-4 video prompting guide, which documents how their model responds to layered motion descriptions. It is a reasonable template for any text-to-video tool, including SentX, but Runway's specific syntax and controls are not proof that SentX interprets every phrase identically. Treat it as a structure to adapt, not a guaranteed command set.

The core principle: start with the simplest version of the motion you want, get that working, then add detail one element at a time. A useful breakdown has four layers.

1. Subject motion. What the main character or object does. Plain physical verbs: turns, walks, reaches, lifts, drifts, settles. If there are multiple subjects, identify them by position ("the person on the left") or a simple descriptor ("the woman nods"). If you are animating a still image, do not restate the visual details the image already shows; focus the text on what changes over time.

2. Scene motion. How the environment reacts or moves on its own. You can imply it through adjectives ("dusty desert," "neon-lit street") or state it directly ("dust trails behind the subject as they move"). Implied motion keeps the environment in the background; direct description makes it stand out.

3. Camera motion. Start with one camera action per clip — locked, handheld, slow push-in, pan, dolly, tracking. If a clip feels unfocused, cutting back to a single move is the first thing to try.

4. Style descriptor. A short tag for overall treatment: cinematic live-action, smooth animation, documentary handheld. This sets texture, not plot.

A practical starting point for a five-second social clip: one subject action, one environmental detail, and one camera direction. If the output gets muddled, trim toward that before adding more.

Aspect ratio and platform fit

SentX documents three output shapes: landscape, square, and vertical 9:16. Vertical 9:16 is the native frame for Instagram Reels, TikTok, and YouTube Shorts, so it is the default for short-form social. Square suits feed posts that crop differently. Landscape fits web embeds or YouTube. Pick the ratio before generating, because each regeneration draws on your media allowance.

Reviewing the clip before you publish

When the generation finishes, watch it at the size you will actually post. Four checks matter:

• Does the subject match what you described?
• Is the composition clean enough for the platform's overlay area (captions, UI chrome)?
• Does the motion read clearly in a single pass, or does it need a second viewing to parse?
• Does the style hold consistently across the clip, or does it drift?

If one of those fails, change only that variable in the next prompt. Keep the parts that worked. Rewriting the entire prompt discards the elements that were already functioning.

What the free tier covers and what it does not

A registered SentX account includes one free video generation at 480p, up to five seconds, with no reference video as input. That is a one-time allowance, not a daily grant. After it, further video generations draw from your prepaid wallet balance unless a Plus subscription allowance applies. Anonymous chat does not include media generation; a signed-in account is required.

The product pages do not document a fixed maximum duration beyond the five-second free tier, do not confirm whether audio is generated alongside video, and do not specify exact motion-adherence guarantees. Those remain open questions rather than features you can plan around.

What your submission becomes

This is the boundary most readers skip. SentX's published privacy policy states that content you submit is not confidential. Retained representations of your interactions can enter a shared memory system and surface in other users' sessions. The license granted at submission is perpetual and survives account deletion for material already incorporated into training data, model weights, or shared memory. In practice: do not paste client names, unreleased product specs, proprietary brand assets, or internal strategy into prompts, and do not upload images containing them.

The generator is a drafting tool for motion concepts, not a replacement for footage you cannot afford to lose. When a clip works, save the final video, the last prompt you used, and the brief text outside the platform.