viralvideo

final_video.mp4

Generate TikTok-style vertical videos (9:16) that sync clips to a music template's bass pattern. When bass drops, the last frame freezes; when it lifts, the next clip plays. Ends with a 4-second SUBSCRIBE outro.

Install

pip install viralvideo

Or from source:

git clone https://github.com/maxylev/viralvideo.git
cd viralvideo
pip install -e .

External dependencies

These must be installed separately — they are not bundled with the Python package:

Tool	Install	Needed for
ffmpeg	brew install ffmpeg or ffmpeg.org	All stages
ffprobe	Included with ffmpeg	All stages
Node.js	brew install node or nodejs.org	yt-dlp YouTube signature solving
OpenRouter API key	openrouter.ai	--stage final only

The CLI checks for ffmpeg and ffprobe at startup and exits with install instructions if missing.

Installed automatically via pip:

Package	Purpose
yt-dlp	YouTube video downloading
numpy / scipy	Bass detection audio analysis
requests	OpenRouter API calls

Quick start

# Create a URL file (see URL format below)
cat > urls.txt << 'EOF'
https://www.youtube.com/watch?v=VIDEO_ID?start=00:01:16&crop=left:15
https://www.youtube.com/watch?v=VIDEO_ID?start=00:00:30
EOF

# Test run — preview timing and cropping, no API calls
viralvideo upscale -i urls.txt -s test

# Final run — enhance freeze frames, produce final video
viralvideo upscale -i urls.txt -s final

Command reference

viralvideo upscale [OPTIONS]

Required:

Option	Flag	Description
--input	-i	Text file with YouTube URLs (one per line)
--stage	-s	test, final, or final:RANGE

Optional:

Option	Flag	Default	Description
--audio	-a	bass_pulse	Audio template: built-in name or path to .wav/.mp4
--resolution	-r	1080x1920	Output resolution in WxH format
--output	-o	output/ next to input file	Output directory
--outro-text		SUBSCRIBE	Text shown on the outro screen (seconds 20–24)
--model	-m	google/gemini-3.1-flash-image-preview	OpenRouter model for frame enhancement
--api-key		$OPENROUTER_API_KEY	OpenRouter API key (or set env var)

Stage values

Value	Behavior
test	Build video with raw freeze frames — no API calls
final	Enhance all freeze frames via OpenRouter
final:1	Enhance only video 1, reuse cached frames for the rest
final:2-4	Enhance videos 2, 3, 4; reuse cached for 1 and 5
final:1,3-5	Enhance videos 1, 3, 4, 5

Specifying a video number in the range always calls the API, overwriting any cached enhanced frame. Videos not in the range reuse a cached enhanced_*.png if it exists.

Resolution examples

viralvideo upscale -i urls.txt -s test -r 1080x1920   # TikTok 1080p
viralvideo upscale -i urls.txt -s test -r 720x1280    # 720p
viralvideo upscale -i urls.txt -s test -r 540x960     # 540p (fast preview)

Audio templates

The --audio flag accepts a built-in name or a file path:

# Built-in (ships with the package)
viralvideo upscale -i urls.txt -s test -a bass_pulse

# Custom audio
viralvideo upscale -i urls.txt -s test -a /path/to/my_template.wav
viralvideo upscale -i urls.txt -s test -a /path/to/my_template.mp4

Name	Description
bass_pulse	5-bass-note pattern at ~2s intervals, 24s total

Model selection

# Default model
viralvideo upscale -i urls.txt -s final -m google/gemini-3.1-flash-image-preview

# Alternative model
viralvideo upscale -i urls.txt -s final -m google/gemini-2.5-flash

Outro text

The last 4 seconds show a black screen with centered text. Customize or disable:

viralvideo upscale -i urls.txt -s test --outro-text "FOLLOW FOR MORE"
viralvideo upscale -i urls.txt -s test --outro-text ""             # black screen, no text

Output directory

By default, outputs go to output/ next to the input file. Redirect with --output:

viralvideo upscale -i urls.txt -s test -o /tmp/my_video

URL file format

One URL per line. Each URL supports start and crop parameters:

https://www.youtube.com/watch?v=VIDEO_ID?start=HH:MM:SS&crop=SIDE[:PCT]

Parameter	Required	Description
start	yes	Playback start offset (HH:MM:SS, MM:SS, or seconds)
crop	no	Crop alignment: left, right, center, top, bottom
crop pct	no	Percentage shift from center. 0 = center, 100 = fully to that edge. Bare crop=left defaults to 100%.

Examples

# Center crop (default)
https://www.youtube.com/watch?v=abc123?start=00:01:16

# Full left crop
https://www.youtube.com/watch?v=abc123?start=00:01:16&crop=left

# 15% shift left from center
https://www.youtube.com/watch?v=abc123?start=00:01:16&crop=left:15

# Full bottom crop
https://www.youtube.com/watch?v=abc123?start=00:00:30&crop=bottom

# 30% shift down from center
https://www.youtube.com/watch?v/abc123?start=00:00:30&crop=bottom:30

5 URLs = 5 videos, one per bass note detected in the template.

How it works

Template audio
──────────────╥────────────────────╥──────────────────╥─── ...
              ║ BASS               ║ BASS              ║
              ║                    ║                    ║
Video         ║                    ║                    ║
── vid 1 ────║── freeze ──────────║── vid 2 ──────────║── freeze ── ...
              ║ (last frame vid 1) ║                    ║ (last frame vid 2)

1. Analyze the template audio for bass notes using hysteresis threshold on low-frequency RMS
2. Download each YouTube URL at its start offset via yt-dlp
3. Crop each video to 9:16 using the crop parameter for vertical framing
4. Segment: play during vocals/silence, freeze on the last frame during bass, outro with customizable text for seconds 20–24
5. Enhance freeze frames via OpenRouter API (final stage only)
6. Assemble all segments at 30fps at the target resolution, mux with audio, trim to 24 seconds

Crop behavior

All videos are cropped to 9:16. The crop parameter controls framing:

• Landscape (wider than 9:16): left/right shift horizontal crop
• Portrait (narrower than 9:16): top/bottom shift vertical crop
• Percentage: crop=left:0 = center, crop=left:50 = halfway, crop=left:100 = fully left

Changing the crop parameter changes the cached filename, so re-running with a different crop will re-crop automatically.

Output files

Outputs go to an output/ directory next to the input file by default, or wherever --output points:

output/
├── test/                    # --stage test
│   ├── source_*.mp4             Downloaded videos
│   ├── cropped_*.mp4            9:16 cropped videos
│   ├── seg_*.mp4                Individual segments
│   ├── play_last_*.png          Extracted last frames
│   └── test_video.mp4          Final test video
└── final/                   # --stage final
    ├── (same as test/)
    ├── enhanced_*.png            AI-upscaled freeze frames
    └── final_video.mp4          Final enhanced video

Cookies for yt-dlp

If downloads fail due to authentication, place a cookies.txt (Netscape format) next to your input file. It will be picked up automatically.

Development

pip install -e ".[dev]"
pytest

Project structure

src/viralvideo/
├── __init__.py          Version + built-in audio registry
├── cli.py               CLI entry point + dependency checks
├── upscale.py           Upscale video type (play/freeze/bass)
├── audio.py             Bass detection & segment analysis
├── downloader.py        YouTube download & URL parsing
├── enhance.py           OpenRouter frame enhancement
├── ffmpeg_tools.py      ffmpeg/ffprobe wrappers & crop logic
└── assets/audio/
    └── bass_pulse.wav   Built-in audio template

License

MIT