video-generation

Original：🇺🇸 English

Translated

Guide to video generation in MassGen. Use when creating videos from text prompts or images across Grok, Google Veo, and OpenAI Sora backends.

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Sourcemassgen/massgen

Added on2026-04-02

NPX Install

npx skill4agent add massgen/massgen video-generation

SKILL.md Content

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Video Generation

Generate videos using

generate_media

with

mode="video"

. The system auto-selects the best backend based on available API keys.

Quick Start

python

# Simple text-to-video (auto-selects backend)
generate_media(prompt="A robot walking through a city", mode="video")

# Specify backend and duration
generate_media(prompt="Ocean waves crashing on rocks", mode="video",
               backend_type="google", duration=8)

# With aspect ratio
generate_media(prompt="A timelapse of clouds", mode="video",
               backend_type="grok", aspect_ratio="16:9", duration=10)

Backend Comparison

Backend	Default Model	Duration Range	Default Duration	Resolutions	API Key
Grok (priority 1)	`grok-imagine-video`	1-15s	5s	480p, 720p	`XAI_API_KEY`
Google Veo (priority 2)	`veo-3.1-generate-preview`	4-8s	8s	720p, 1080p, 4K (use `size` ); default 16:9	`GOOGLE_API_KEY`
OpenAI Sora (priority 3)	`sora-2`	4, 8, or 12s (discrete)	4s	Standard	`OPENAI_API_KEY`

Key Parameters

Parameter	Description	Example
`prompt`	Text description of the video	`"A drone flying over mountains"`
`backend_type`	Force a specific backend	`"grok"` , `"google"` , `"openai"`
`model`	Override default model	`"veo-3.1-generate-preview"`
`duration`	Video length in seconds	`8` (clamped to backend limits)
`aspect_ratio`	Video aspect ratio	`"16:9"` , `"9:16"` , `"1:1"`
`size`	Resolution (Grok: 480p/720p; Veo: 720p/1080p/4k)	`"720p"` , `"1080p"` , `"4k"`
`input_images`	Source image for image-to-video	`["starting_frame.jpg"]`
`video_reference_images`	Style/content guide images (Veo, up to 3)	`["ref1.png", "ref2.png"]`
`negative_prompt`	What to exclude (Veo)	`"blurry, low quality"`

Duration Handling

Each backend has different duration constraints.

generate_media

automatically clamps the requested duration:

Grok: Continuous range 1-15s (clamped to bounds)
Google Veo: Continuous range 4-8s (clamped to bounds), defaults to 16:9 aspect ratio
OpenAI Sora: Discrete values only (4, 8, or 12s) - snaps to nearest valid value

A warning is logged if duration is adjusted.

Image-to-Video

All three video backends support starting video from an existing image via

input_images

python

generate_media(
    prompt="Animate this scene with gentle movement",
    mode="video",
    input_images=["scene.jpg"],
    duration=5
)

The first image in

input_images

is used; additional images are ignored.

Generation Time

Video generation is significantly slower than images. All backends use polling:

Grok: SDK handles polling internally (up to 10 min timeout)
Google Veo: Custom polling every 20s (up to 10 min)
OpenAI Sora: Custom polling every 2s

Veo 3.1: Native Audio

Veo 3.1 generates audio (dialogue, SFX, ambient) automatically from prompt content. No extra parameter needed — just describe the sounds:

Dialogue: Use quotation marks in prompt (
```
"Hello," she said.
```
)
Sound effects: Describe sounds (
```
tires screeching, engine roaring
```
)
Ambient: Describe atmosphere (
```
eerie hum resonates through the hallway
```
)

Veo 3.1: Extension Constraints

When extending videos via

continue_from

with a

veo_vid_*

ID:

Resolution is forced to 720p (API requirement for extensions)
Only 16:9 and 9:16 aspect ratios are supported
Each extension adds up to 7 seconds (API limit: 20 extensions, ~141s total)
Generated videos are retained for 2 days before expiry

Producing Longer Videos

Current APIs cap at 15 seconds max per clip (Grok), with most backends at 4-8s. There is no way to generate a continuous 30+ second video in one call. The proven approach:

Plan a shot list — break your video into 6-8s segments with specific camera language per shot
Generate clips in parallel — launch all segments concurrently using
```
background=True
```
Composite in Remotion (see below) — layer programmatic animation on top of generated footage
Bridge with audio — a unified narration or music track smooths over visual cuts between clips

For visual continuity, use the same style anchor in every prompt (e.g., "BBC Earth documentary cinematography") and maintain consistent lighting/color descriptions.

Full production guide with examples, transition types, and duration strategy: See references/production.md

Hybrid Workflow: AI Footage + Remotion Animation

The best results come from combining AI-generated footage with Remotion's programmatic animation — not choosing one or the other.

AI video generation produces photorealistic, cinematic footage that pure programmatic rendering cannot match. Remotion produces precise typography, motion graphics, overlays, and transitions that AI generation cannot reliably control. Use both together.

The Rule: Generate First, Composite Second

Generate AI clips for cinematic/photorealistic shots (environments, product demos, atmospheric footage)
Use those clips as visual foundations in Remotion — import them as
```
<Video>
```
or
```
<OffthreadVideo>
```
background layers
Composite programmatic elements on top — typography, motion graphics, logos, data overlays, transitions, captions
Fill gaps with pure Remotion animation — title cards, intro sequences, motion-graphics-only segments where AI footage isn't needed

Do NOT Discard Generated Clips

Every AI-generated clip costs real money and time. Do not abandon generated footage and fall back to purely programmatic rendering. This is a common failure mode — agents generate clips, notice minor artifacts (e.g., repeated patterns, slight distortion), then pivot entirely to OpenCV/PIL/moviepy rendering, wasting all the generation budget.

Instead:

Situation	Wrong Approach	Right Approach
Minor artifacts in generated clip	Discard clip, render from scratch with OpenCV	Use clip as background, mask artifacts with overlays/motion graphics
Generated clip doesn't match vision exactly	Regenerate or abandon	Composite typography/effects on top to guide the viewer's attention
Need precise text/logo placement	Skip AI generation, use pure programmatic	Generate atmospheric footage, overlay text in Remotion
Some shots need AI footage, others don't	Use one approach for everything	Mix: AI-backed shots + pure Remotion animation shots

Cost Awareness

Each

generate_media(mode="video")

call is expensive. Plan before generating:

Decide which shots need AI footage before generating anything — not every shot needs it
Generate only what you'll use — don't speculatively generate 8 clips hoping some work out
Review and use what you generate — analyze each clip with
```
read_media
```
, then plan your Remotion composition around actual footage
One good clip composited well beats five unused clips — invest in composition quality over generation quantity

Post-Production: Always Use Remotion

Remotion is the default post-production tool for any video that needs editing beyond simple concatenation. This includes captions, titles, transitions, overlays, motion graphics — essentially any video intended to look professional. Do not use raw ffmpeg

drawtext

or manual filter chains for these tasks; the results look amateur compared to what Remotion produces.

When you have video clips to assemble, load the Remotion skill and use it. This is not optional for professional output.

Loading the Remotion Skill

Load the skill to get detailed rules and code examples:

Local path (if installed via quickstart):
```
.agent/skills/remotion/SKILL.md
```
Remote repo (if not installed): https://github.com/remotion-dev/skills

What Remotion Gives You

Capability	Remotion	Raw ffmpeg
Styled animated captions	CSS-styled, word-level highlighting, animations	`drawtext` — ugly, painful escaping
Title cards / lower thirds	React components, any font/layout	Manual positioning, limited fonts
Scene transitions	Timing curves, spring animations, custom effects	Basic xfade (fade, wipe)
Motion graphics	Full React/CSS/Three.js/Lottie ecosystem	Not possible
Light leak / overlay effects	Built-in `@remotion/light-leaks`	Complex filter chains
Text animations	Typography effects, per-character animation	Not feasible
AI footage + overlays	Import clips as `<Video>` , layer React components on top	Not feasible at quality

When ffmpeg Alone Is Sufficient

Only use ffmpeg without Remotion for:

Concatenating clips with no captions, titles, or transitions (just hard cuts)
Audio mixing / ducking (ffmpeg or Pydub)
Color grading via LUT files (
```
lut3d
```
filter)
Quick format conversion or rescaling

Workflow

Generate AI clips with
```
generate_media
```
(parallel, background mode) — for shots that need cinematic/photorealistic quality
Review clips with
```
read_media
```
— assess what you have, plan composition around actual footage
Generate audio (narration, music) with
```
generate_media(mode="audio")
```
Load the Remotion skill and set up a Remotion project
Composite in Remotion: import AI clips as
```
<Video>
```
background layers, overlay typography/motion graphics/captions, add pure-animation segments for title cards and transitions
Render via Remotion's headless renderer

Key Remotion Rule Files to Load

When working on a specific task, load the relevant rule files from the Remotion skill:

Captions/subtitles:

rules/subtitles.md

rules/display-captions.md

rules/transcribe-captions.md

Transitions:
```
rules/transitions.md
```
Text animations:
```
rules/text-animations.md
```
Light leaks:
```
rules/light-leaks.md
```

Audio:

rules/audio.md

rules/audio-visualization.md

Sequencing/timeline:
```
rules/sequencing.md
```
,
```
rules/trimming.md
```
3D motion graphics:
```
rules/3d.md
```
Animations/timing:
```
rules/animations.md
```
,
```
rules/timing.md
```

Need More Control?

Per-backend resolution, duration details, and quirks: See references/backends.md
Video continuation, remix, and image-to-video: See references/editing.md
Multi-shot production, transitions, and cinematic workflow: See references/production.md