Youtube Shorts Generator

---
name: youtube-shorts-generator
description: Generate viral 9:16 YouTube Shorts (or TikTok/Reels clips) from a long-form YouTube URL or local video. Triggers on requests like "make shorts from this video", "extract viral clips from this YouTube link", "auto-clip this podcast", "find the best moments and crop vertical". Pipeline downloads the source, transcribes via MuAPI /openai-whisper, ranks highlights through a virality framework (hook / emotional peak / opinion bomb / revelation / conflict / quotable / story peak / practical value), dedupes overlapping candidates, and vertically auto-crops the top N as mp4s.
---

# YouTube Shorts Generator

End-to-end pipeline that turns one long video into N viral-ready vertical clips. Each clip ships with a viral score (0–100), an opening hook line, and a one-sentence reason it should perform.

Reference implementation: https://github.com/SamurAIGPT/AI-Youtube-Shorts-Generator

## When to use this skill

- "Generate shorts from this YouTube video"
- "Find the most viral 60-second clips in this podcast"
- "Auto-crop this interview to 9:16"
- "Give me TikTok clips from this lecture"

If the user only wants transcription, summarization, or thumbnails — this is the wrong skill.

## Inputs to collect before running

Ask once, then proceed:
1. **Source** — YouTube URL (preferred) or path/URL to an mp4
2. **`num_clips`** — default 3
3. **`aspect_ratio`** — default `9:16` (also: `1:1`, `4:5`)
4. **`language`** — default auto-detect (forwarded to MuAPI Whisper as ISO-639-1)
5. **Output JSON path** — optional; if set, dump full result there

If the user gave a URL and nothing else, use defaults and don't block on questions.

## Prerequisites (verify before first run)

- Python 3.10+
- A MuAPI key — set `MUAPI_API_KEY` in `.env`. Powers download, transcription, highlight ranking, and clipping. If missing, stop and ask the user for it; do not invent one.
- `pip install -r requirements.txt` inside a venv

If the repo isn't cloned yet, clone `https://github.com/SamurAIGPT/AI-Youtube-Shorts-Generator.git` into the working directory.

## Pipeline (what to execute)

Run the eight stages in order. Each maps to a module in `shorts_generator/`.

1. **Download** (`downloader.py`) — pull the source video at the requested resolution (`360`/`480`/`720`/`1080`, default `720`).
2. **Transcribe** (`transcriber.py`) — MuAPI `/openai-whisper` runs Whisper server-side and returns timestamped `verbose_json` segments. Billed per minute of audio.
3. **Classify content type** — LLM tags the video (podcast / interview / tutorial / vlog / lecture / monologue) and density. Tune the highlight prompt per type.
4. **Chunk if long** (`highlights.py`) — videos > `LONG_VIDEO_THRESHOLD` (1800s default) are split into `CHUNK_SIZE_SECONDS` (1200s default) windows with `CHUNK_OVERLAP_SECONDS` (60s default) overlap so cross-boundary highlights aren't missed.
5. **Rank highlights** — LLM scans each chunk through `VIRALITY_CRITERIA`:
   - **Hook moments** — strong opening line that stops the scroll
   - **Emotional peaks** — laughter, anger, vulnerability, awe
   - **Opinion bombs** — spicy, contrarian, debate-bait takes
   - **Revelation moments** — "wait, what?" reframes
   - **Conflict** — disagreement, tension, callouts
   - **Quotable lines** — tight, screenshot-worthy phrasing
   - **Story peaks** — climax of a narrative arc
   - **Practical value** — actionable insight a viewer will save
   Each candidate gets `start_time`, `end_time`, `score` 0–100, `title`, `hook_sentence`, `virality_reason`. Aim for 30–75s clips unless content dictates otherwise.
6. **Dedupe** — collapse overlaps. Rule: if two candidates overlap > 50%, keep the higher score, drop the other.
7. **Top-N selection** — sort surviving candidates by score, take `num_clips`.
8. **Vertical auto-crop** (`clipper.py`) — render each highlight at `aspect_ratio`. Auto-handles face tracking and screen recordings; no Haar cascades.

## Invocation

CLI (the standard path):

```bash
python main.py "<YOUTUBE_URL>" \
    --num-clips 5 \
    --aspect-ratio 9:16 \
    --output-json result.json
```

Python API (when embedding in another pipeline):

```python
from shorts_generator import generate_shorts

result = generate_shorts(
    "<URL>",
    num_clips=5,
    aspect_ratio="9:16",
)
for short in result["shorts"]:
    print(short["score"], short["title"], short["clip_url"])
```

Batch mode — `urls.txt` with one URL per line:

```bash
xargs -a urls.txt -I{} python main.py "{}"
```

## CLI flags reference

| Flag | Default | Notes |
|------|---------|-------|
| `--num-clips` | `3` | How many shorts to render |
| `--aspect-ratio` | `9:16` | `9:16` for TikTok/Reels, `1:1` square, anything else by flag |
| `--format` | `720` | Source download resolution |
| `--language` | auto | Whisper language code (e.g. `en`) |
| `--output-json` | — | Dump full result (transcript + all candidates + clip URLs) |

## Output schema

```json
{
  "source_video_url": "...",
  "transcript": { "duration": 1873.4, "segments": [...] },
  "highlights": [ /* every candidate, before top-N cut */ ],
  "shorts": [
    {
      "title": "The one mistake that cost me $50K",
      "start_time": 124.3,
      "end_time": 187.6,
      "score": 92,
      "hook_sentence": "Nobody talks about this, but it killed my first startup...",
      "virality_reason": "Opens with a number + regret, peaks on a contrarian lesson",
      "clip_url": "https://.../short_1.mp4"
    }
  ]
}
```

When reporting back to the user, surface for each clip: rank, score, time range, title, hook, and clip URL. Skip the raw transcript unless asked.

## Tunable knobs

- `shorts_generator/highlights.py`
  - `VIRALITY_CRITERIA` — reorder or extend signals
  - `HIGHLIGHT_SYSTEM_PROMPT` — duration sweet spot, hook rules, JSON schema
  - `CHUNK_SIZE_SECONDS` — 1200s default
  - `LONG_VIDEO_THRESHOLD` — 1800s default
  - `CHUNK_OVERLAP_SECONDS` — 60s default
- `shorts_generator/config.py` (or env vars)
  - `MUAPI_POLL_INTERVAL` — 5s
  - `MUAPI_POLL_TIMEOUT` — 1800s

## Whisper transcription

Audio is transcribed by MuAPI's `/openai-whisper` endpoint (server-side `whisper-1`, billed per minute). The CLI passes `--language` straight through; leave it empty for auto-detection, or pass an ISO-639-1 code (e.g. `en`) to lock it.

## Failure modes — handle, don't paper over

- **Whisper produced no segments** — likely no detectable speech or a hard language. Retry with `--language <code>` (correct ISO-639-1) before declaring failure.
- **API key missing or rejected** — surface the exact error; never fabricate a key.
- **Job timed out** — bump `MUAPI_POLL_TIMEOUT` and retry; don't silently truncate.
- **Highlight ranker returned <`num_clips`** — return what survived dedupe with a note; don't pad with low-score filler.

## Done criteria

The skill is done when:
1. `result["shorts"]` has up to `num_clips` entries, each with a working `clip_url`.
2. The user has been shown the ranked list (score, time range, title, hook, URL).
3. If `--output-json` was set, the file exists and parses.

If any clip URL 404s on a HEAD check, re-run just the crop stage for that highlight rather than re-running the whole pipeline.