AI Reels generator: size, length and sound for Instagram Reels and Shorts
Reels and Shorts reward the same thing: a vertical clip that hooks in the first second. Here is how to set up the AI Video Generator for 9:16, pick a length that holds attention, decide when to keep native sound, and ten ready-to-use Reel ideas with prompts, models and credits.
· 6 min read · 827 views · by the Cortex Digital Hub team
Set Format to 9:16, Length to 5 to 15 seconds, and sound off if you plan to add a trending track. Pick a model, check the credit total, and generate your Reel. From ₹24 a clip · no watermark · runs in your browser
Make a video → → Opens AI Video Generator · runs in your browser
Reels and Shorts are the same shape, the same length range and mostly the same audience habits, so one AI clip can serve both if you set it up right at the start. The settings that matter are format, length and sound, and all three are chosen before you press Generate in the AI Video Generator. This post covers those three choices, gives ten Reel ideas for Indian creators and small businesses with prompts and credit costs, and ends with the few places where Shorts and Reels differ.
Format: 9:16, set before you generate
Both platforms play full-screen vertical video, and the standard size is 1080 by 1920 pixels. Pick 9:16 under Format in the generator rather than making a 16:9 clip and cropping it later. The model composes the shot for the frame it is given; a 9:16 prompt puts the subject in the centre with headroom, while a cropped landscape clip loses the edges and often the subject with them.
If you have an older clip in the wrong shape, the free resize to 1080x1920 tool crops it on your device, and the Reels resizing guide walks through the safe zones so your subject does not sit behind the caption or the like button. Keep anything important in the middle 70 percent of the frame; both apps overlay their interface at the bottom and down the right side.
Length: 5 to 15 seconds, and when to go multi-shot
A Reel wins or loses in the first second, so a 5-second clip with one strong motion is often the best use of credits. A chai being poured, a saree catching the light, a flat's balcony door sliding open: one subject, one camera move, done.
When you want a small story, use a 15-second clip on a multi-shot model. Lumen Motion 3 and Orbit 2.6 can hold three or four scenes in one generation if you describe them in order: "three shots: a barista pours filter coffee, a hand places a plate of vada on a table, two friends laugh at a window seat." The model cuts between them, and the result reads like an edited Reel without any editing.
Both platforms accept videos longer than this as of 2026, but check each one's help page for the current limit before planning a long piece. For anything past 30 seconds, make it in parts and join them with the free trim and converter tools.
Sound: off for a trending track, on for ambience
The sound toggle decides whether the model generates audio with the picture: ambience, effects and music that match the motion. There is no voice-over unless the prompt asks for speech.
Turn it off when you plan to add a trending track inside Instagram or YouTube. A clip with its own music underneath a trending audio sounds muddy, and you lose the clean track you picked the song for in the first place.
Turn it on when the sound is the hook. Rain on a Mumbai street, oil sizzling in a kadai, a crowded Chennai market, fireworks over a pandal: these land harder with native audio than with any track you could add. Lumen Motion 2.6 is the pick when you want a line of dialogue, such as a vendor calling out a price.
Ten Reel ideas with prompts, models and credits
Credits are charged per second, 1 credit is ₹0.50, and the exact total shows on the Generate button. Prices below are as of October 2026 at 9:16.
| Reel idea | Prompt | Model and length | Credits | Sound |
|---|---|---|---|---|
| Kirana store Diwali greeting | "a small grocery shop front at dusk, strings of warm lights switch on one by one, diyas on the counter, slow push in" | Orbit 3, 720p, 5 s | 135 (₹68) | Off |
| Boutique saree reveal (image to video) | "slow light sweep across the fabric, camera tilts up along the pallu, threads catch the light" | Lumen Motion 3 Standard, 5 s | 115 (₹58) | Off |
| Cloud kitchen biryani | "slow dolly in on a handi of biryani, steam rising, saffron rice, soft window light, shallow depth of field" | Lumen Motion 3 Standard, 5 s | 115 (₹58) | On |
| Flat launch teaser | "slow glide through a sunlit living room toward a balcony, city skyline beyond, curtains move gently" | Lumen Motion 3 1080p, 8 s | 296 (₹148) | Off |
| Rooftop yoga studio | "sunrise yoga class on a Bangalore rooftop, slow orbit around the group, soft haze over the city" | Orbit 3, 1080p, 6 s | 318 (₹159) | Off |
| Wedding invite teaser | "marigold garlands sway in a breeze, a brass lamp flickers, slow pan across a decorated mandap at golden hour" | Nova 2K, 5 s | 175 (₹88) | Off |
| Café day in three scenes | "three shots: a barista pours filter coffee, a hand places a plate of vada, two friends laugh at a window seat, warm morning light" | Lumen Motion 3 Standard, 15 s | 345 (₹173) | On |
| Monsoon street mood | "rain on a Mumbai street at night, neon reflections in puddles, umbrellas pass, slow motion" | Nova Lite, 6 s | 48 (₹24) | On |
| Phone case unboxing (image to video) | "the case rotates slowly on the spot, a soft light sweep over the surface, plain background" | Nova Lite, 6 s | 48 (₹24) | Off |
| Chai vendor with a line | "a chai vendor at a Delhi roadside stall pours tea from a height, looks at the camera and says 'cutting chai, boss', smiles" | Lumen Motion 2.6, 5 s | 95 (₹48) | On |
Draft the risky ones on Nova Lite first. If the motion works at ₹24, remake it on Lumen Motion 3 for the final; if the model fails or declines, the credits come back automatically.
Shorts vs Reels: the few real differences
The clip is the same, but the surroundings differ. Shorts live inside YouTube search, so a clear title with the words people type ("Hyderabad biryani recipe short") keeps earning views for weeks. Reels are feed-driven and peak within a day or two, so the caption and the audio you attach matter more than the title.
Shorts tolerate a slightly slower, more explanatory clip; a 15-second three-scene café story does fine there. Reels reward the fastest possible hook, so lead with your best second. On music, both platforms let you attach licensed tracks from their own libraries; what you can use for a business account varies, so as of 2026 check each platform's help page before building a campaign on a particular song.
One practical habit: generate once at 9:16, export two copies, and post the Short with a searchable title and the Reel with a trending track. Same credits, two placements.
Finish free, then post
Download the clip within 7 days, since history is cleared after that. Then finish on your device with the free video tools: trim the first half-second if the motion takes a beat to start, add a caption or logo, and compress if your upload is slow. Nothing is uploaded to a server for these steps, and there is no watermark on the clip at any point.
If you are also sending the Reel to a WhatsApp Status or a customer group, the best video format guide covers the one export that works everywhere. Open the AI Video Generator, set 9:16, and try the ₹24 monsoon street prompt first; it is the quickest way to see what a Reel-shaped AI clip looks like.
Frequently asked questions
What size should an AI-generated Reel be?
9:16 at 1080 by 1920 pixels. Set Format to 9:16 in the AI Video Generator before you generate so the model composes for a phone screen, and use the free resizer only if you need to reshape an older clip.
How long should an AI Reel or Short be?
5 to 15 seconds works best for AI clips. A 5-second clip is one strong hook; a 15-second clip on a multi-shot model can hold three or four scenes. Both platforms accept longer videos, but check their help pages for current limits as of 2026.
Should I keep the generated sound or add a trending track?
Turn sound off if you plan to add a trending track inside Instagram or YouTube, since two audio tracks fight. Keep sound on when the ambience is the point: sizzling food, rain, a market, a crowd.
How much does one Reel cost to generate?
As of October 2026, a 6-second draft on Nova Lite is 48 credits (₹24), a 5-second clip on Lumen Motion 3 Standard is 115 credits (about ₹58), and a 15-second multi-shot clip on the same model is 345 credits (about ₹173).