OpenCap Visualizer

Generate videos from OpenCap biomechanics data files with both command-line interface and Python API.

This tool uses the deployed OpenCap Visualizer to create videos from biomechanics data files (.json, .osim/.mot pairs) using headless browser automation.

Features

• Dual Interface: Both command-line tool and Python API
• No Local Setup Required: Uses deployed web application by default
• Multiple Data Formats: Supports JSON files and OpenSim .osim/.mot pairs
• Subject Comparison: Generate videos with multiple subjects
• Anatomical Camera Views: Use biomechanics-friendly camera angles
• Customizable: Colors, zoom, centering, loops, and dimensions
• Automatic 3D Geometry: Loads realistic human models from cloud storage

Installation

pip install opencap-visualizer

Note: After installation, you'll need to install browser dependencies:

playwright install chromium

Command Line Usage

Basic Examples

# Single subject
opencap-visualizer data.json -o output.mp4

# Multiple subjects comparison
opencap-visualizer subject1.json subject2.json -o comparison.mp4

# With custom settings
opencap-visualizer data.json --camera anterior --colors red --loops 2 -o front_view.mp4

# OpenSim files
opencap-visualizer model.osim motion.mot -o simulation.mp4

Advanced Examples

# Multiple subjects with different colors
opencap-visualizer s1.json s2.json s3.json --colors red green blue --camera sagittal -o side_comparison.mp4

# High-resolution with custom zoom
opencap-visualizer data.json --width 3840 --height 2160 --zoom 0.8 --camera superior -o 4k_top_view.mp4

# Interactive mode for manual exploration
opencap-visualizer data.json --interactive --camera anterior

Camera Views

Anatomical Views (Recommended)

• anterior / frontal / coronal - Front-facing view
• posterior - Back view
• sagittal / lateral - Side profile view
• superior - Top-down view
• inferior - Bottom-up view

Technical Views

• top, bottom, front, back, left, right
• isometric, default
• Corner views: frontTopRight, backBottomLeft, etc.

Command Line Options

positional arguments:
  FILE                  Data files (.json, or .osim/.mot pairs)

optional arguments:
  -o, --output PATH     Output video file (default: animation_video.mp4)
  --camera VIEW         Camera position (default: isometric)
  --colors COLOR...     Subject colors (hex or names: red, blue, #ff0000)
  --loops N             Animation loops to record (default: 1)
  --width PX            Video width (default: 1920)
  --height PX           Video height (default: 1080)
  --zoom FACTOR         Zoom factor (>1.0 = zoom out, default: 1.5)
  --no-center           Disable auto-centering on subjects
  --timeout SEC         Loading timeout in seconds (default: 120)
  --interactive         Open browser for manual exploration
  --vue-app-path PATH   Custom Vue app index.html path
  --dev-server-url URL  Custom Vue development server URL
  -v, --verbose         Enable verbose output

Python API Usage

Basic Examples

import opencap_visualizer as ocv

# Simple usage
success = ocv.create_video("data.json", "output.mp4")
if success:
    print("Video generated successfully!")

# Multiple subjects with settings
success = ocv.create_video(
    ["subject1.json", "subject2.json"],
    "comparison.mp4", 
    camera="anterior",
    colors=["red", "blue"],
    loops=2,
    verbose=True
)

Class-based Usage

import opencap_visualizer as ocv

# Create visualizer instance
visualizer = ocv.OpenCapVisualizer(verbose=True)

# Generate video synchronously
success = visualizer.generate_video_sync(
    input_files=["subject1.json", "subject2.json"],
    output_path="comparison.mp4",
    camera="sagittal", 
    colors=["#ff0000", "#00ff00"],
    width=1920,
    height=1080,
    zoom=1.2
)

print(f"Success: {success}")

Async Usage

import asyncio
import opencap_visualizer as ocv

async def generate_videos():
    # Using convenience function
    success = await ocv.create_video_async(
        "data.json", 
        "output.mp4",
        camera="anterior",
        colors=["blue"]
    )
    
    # Using class
    visualizer = ocv.OpenCapVisualizer(verbose=True)
    success = await visualizer.generate_video(
        ["s1.json", "s2.json", "s3.json"],
        "triple_comparison.mp4",
        camera="posterior",
        colors=["red", "green", "blue"],
        center_subjects=True,
        zoom=1.5
    )
    
    return success

# Run async function
success = asyncio.run(generate_videos())

API Reference

OpenCapVisualizer Class

class OpenCapVisualizer:
    def __init__(self, verbose: bool = False)
    
    async def generate_video(
        self,
        input_files: Union[str, List[str]],
        output_path: str = "animation_video.mp4",
        *,
        vue_app_path: Optional[str] = None,
        dev_server_url: Optional[str] = None,
        width: int = 1920,
        height: int = 1080,
        timeout_seconds: int = 120,
        loops: int = 1,
        camera: Optional[str] = None,
        center_subjects: bool = True,
        zoom: float = 1.5,
        colors: Optional[List[str]] = None,
        interactive: bool = False
    ) -> bool
    
    def generate_video_sync(self, ...) -> bool  # Synchronous wrapper

Convenience Functions

async def create_video_async(input_files, output_path, **kwargs) -> bool
def create_video(input_files, output_path, **kwargs) -> bool

Data Formats

JSON Files

The tool accepts biomechanics JSON files with the following structure:

{
  "Data": {
    "ModelScalingVars": "path/to/model.osim",
    "Results": "path/to/motion.mot",
    "FrameTimesOG": [0.0, 0.033, 0.066, ...]
  }
}

OpenSim Files

Alternatively, provide .osim (model) and .mot (motion) file pairs:

opencap-visualizer model.osim motion.mot -o output.mp4

Dependencies

The tool automatically detects the best available option:

1. Deployed Version (Recommended): https://opencap-visualizer.onrender.com/

   • No local setup required
   • Always up-to-date
   • Requires internet connection

2. Local Development Server: http://localhost:3000

   • Start with npm run serve in the Vue.js project
   • Faster for development/testing

3. Built Files: Local dist/index.html

   • Build with npm run build in the Vue.js project
   • Works offline

Configuration

Custom Servers

# Use local development server
opencap-visualizer data.json --dev-server-url http://localhost:3000

# Use custom built files
opencap-visualizer data.json --vue-app-path /path/to/dist/index.html

Environment Variables

# Set default development server
export OPENCAP_DEV_SERVER=http://localhost:3000

Troubleshooting

Browser Installation

If you get browser-related errors:

playwright install chromium

Connection Issues

• Check internet connection for deployed version
• For local development: npm run serve in Vue project
• For built files: npm run build in Vue project

File Format Issues

• Ensure JSON files contain valid biomechanics data structure
• For OpenSim files, provide both .osim and .mot files
• Check file paths are correct and accessible

Video Generation Issues

• Increase timeout: --timeout 300
• Enable verbose mode: --verbose or verbose=True
• Try interactive mode: --interactive

License

MIT License - see LICENSE file for details.

Contributing

Contributions welcome! Please see the source repository for guidelines.

Support

For issues and questions:

• GitHub Issues: https://github.com/utahmobl/opencap-visualizer/issues
• Web App: https://opencap-visualizer.onrender.com/