AI Video API for Social Media Ads — Which Model Should You Use?

A performance marketer running paid social campaigns typically tests 15–20 ad creative variants — different hooks, different first-three-seconds, different visual styles — before scaling spend behind the two or three that convert. Producing that many variants with a video shoot isn't viable on a weekly testing cadence; generating them via API is, but only if the per-variant cost stays low enough that killing 90% of them after a day of testing doesn't hurt. That makes model choice a cost problem before it's a quality problem.

This is a model comparison: which of GenRelay's video models fits the testing phase where volume matters, and which fits the scaling phase once a winning variant is identified.

What's the Real Cost Difference Between Video Models for Ad Testing?

The gap between cheapest and most expensive is roughly 6x per second, which matters when you're generating dozens of throwaway variants rather than one final asset.

Model	Billing basis	Cost per 6s clip (720p)	Native audio	Best for
Grok Imagine 1.0 (t2v)	Per second	$0.06	No	High-volume hook testing
Gemini Omni Flash	Per generation	$0.10 (flat)	No	Predictable per-variant budgeting
Grok Imagine 1.5 (i2v)	Per second	$0.132	No	Animating existing product/brand imagery
Veo 3.1 Lite	Per second	$0.36	Yes	Winning-variant scale-up with audio

For a 20-variant testing round at 6 seconds each: Grok 1.0 runs 20 × $0.06 = $1.20; Omni Flash runs 20 × $0.10 = $2.00; Veo 3.1 Lite runs 20 × $0.36 = $7.20. Testing the full round on Grok 1.0 first, then re-generating only the top 2–3 performers on Veo 3.1 Lite with audio, costs roughly $2.32 total instead of $7.20 for a full Veo round — the same logic as testing thumbnails before committing to a final render.

Which Model Fits the Testing Phase vs the Scaling Phase?

Grok Imagine 1.0 fits the testing phase because its per-second cost is the lowest of the four and text-to-video generation doesn't require existing creative assets — useful when testing hook concepts from scratch. Omni Flash's flat per-generation billing makes per-variant cost predictable regardless of clip length, which simplifies budgeting when a media buyer needs a fixed cost-per-variant number for a testing plan rather than a per-second calculation. Grok Imagine 1.5's image-to-video mode fits campaigns that animate existing product photography or brand assets rather than generating a scene from a text prompt. Veo 3.1 Lite fits the scaling phase — once a variant is confirmed to convert, regenerating it with Veo 3.1 Lite adds native synchronized audio (voiceover-ready ambient sound and effects), which matters for the version that's about to receive real ad spend.

Definition: native synchronized audio means the model generates sound (ambient noise, effects matched to on-screen motion) as part of the video output itself, rather than requiring a separate text-to-speech or audio mixing step after generation — currently a Veo 3.1 Lite–specific capability among GenRelay's video models.

How Do I Generate Multiple Ad Variants via API?

Submit one job per hook variant with a shared base prompt and a varying opening line, then collect results as they complete.

import requests

API_KEY = "YOUR_GENRELAY_KEY"
BASE_URL = "https://genrelay.ai/v1"

hooks = [
    "Extreme close-up on a running shoe hitting wet pavement, rain splashing",
    "Slow-motion shot of a hand lacing up a running shoe at sunrise",
    "Runner glancing at a smartwatch mid-stride, city street blurred behind them",
]

def submit_variant(hook_prompt, model="grok-imagine-1.0", duration=6):
    response = requests.post(
        f"{BASE_URL}/videos/generations",
        headers={
            "Authorization": f"Bearer {API_KEY}",
            "Content-Type": "application/json"
        },
        json={
            "model": model,
            "prompt": hook_prompt,
            "duration": duration,
            "aspect_ratio": "9:16"
        }
    )
    return response.json()["id"]

job_ids = [submit_variant(h) for h in hooks]

Poll each job ID with the pattern in the async video API polling guide — per-model poll intervals differ, and Grok's jobs typically complete faster than Veo 3.1 Lite's given the shorter per-second render time.

What Aspect Ratio and Duration Should Ad Creative Use?

Vertical 9:16 fits Instagram Reels, TikTok, and Stories placements; square 1:1 or horizontal 16:9 fits Facebook feed and YouTube pre-roll — check the target placement's spec before generating, since re-cropping a generated clip after the fact loses composition control the model had at generation time. Duration should match the platform's optimal hook window: 6 seconds is long enough to establish a visual hook without paying for seconds most viewers won't watch past, and short enough to keep testing-phase cost low across a large variant set. See the short-form video API guide for platform-specific format details.

FAQ

Which model is cheapest for testing a large batch of ad hook concepts?
Grok Imagine 1.0, at $0.010/second — a 6-second clip costs $0.06, the lowest per-variant cost among GenRelay's video models.

Does Omni Flash's flat per-generation pricing make it cheaper than Grok for short clips?
Not for 6-second clips — Grok 1.0 costs $0.06 versus Omni Flash's flat $0.10. Omni Flash's flat billing becomes more competitive as clip length increases, since its cost doesn't scale with duration.

Should the final scaled ad use the same model as the testing round?
Not necessarily. A common pattern is testing cheaply on Grok 1.0, then regenerating only the confirmed winner on Veo 3.1 Lite to add native audio before it receives real ad spend.

Can I generate ad variants in both 9:16 and 16:9 from the same prompt?
Yes — submit separate jobs with different aspect_ratio values. Each generation renders independently, so the same prompt can be run once per target aspect ratio.

Is there a free tier to test ad variant generation before committing budget?
Yes. GenRelay includes free credits on signup, enough to generate a small batch of test variants across models before setting a per-campaign testing budget.

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As of September 2026. Pricing subject to change — verify current rates at genrelay.ai.