# Video Generation

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

- Skill: `massgen/video-generation` (Agent Skill, multi-file: 4 files)
- Install (CLI): `npx skillmds@latest add massgen/video-generation`
- Raw SKILL.md: https://api.skillmd.com/api/skills/massgen/video-generation/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: massgen (https://skillmd.com/u/massgen)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/massgen/video-generation

---


# 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:

1. **Plan a shot list** — break your video into 6-8s segments with specific camera language per shot
2. **Generate clips in parallel** — launch all segments concurrently using `background=True`
3. **Composite in Remotion** (see below) — layer programmatic animation on top of generated footage
4. **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](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

1. **Generate AI clips** for cinematic/photorealistic shots (environments, product demos, atmospheric footage)
2. **Use those clips as visual foundations** in Remotion — import them as `<Video>` or `<OffthreadVideo>` background layers
3. **Composite programmatic elements on top** — typography, motion graphics, logos, data overlays, transitions, captions
4. **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

1. **Generate AI clips** with `generate_media` (parallel, background mode) — for shots that need cinematic/photorealistic quality
2. **Review clips** with `read_media` — assess what you have, plan composition around actual footage
3. **Generate audio** (narration, music) with `generate_media(mode="audio")`
4. **Load the Remotion skill** and set up a Remotion project
5. **Composite in Remotion**: import AI clips as `<Video>` background layers, overlay typography/motion graphics/captions, add pure-animation segments for title cards and transitions
6. **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](references/backends.md)
- **Video continuation, remix, and image-to-video**: See [references/editing.md](references/editing.md)
- **Multi-shot production, transitions, and cinematic workflow**: See [references/production.md](references/production.md)