pixelflux

A performant web native pixel delivery pipeline for diverse sources, blending VNC-inspired parallel processing of pixel buffers with flexible modern encoding formats.

This module provides a Python interface to a high-performance C++ capture library. It captures pixel data from a source (currently X11 screen regions), detects changes, and encodes modified stripes into JPEG or H.264, delivering them via a callback mechanism. This stripe-based, change-driven approach is designed for efficient streaming or processing of visual data.

Installation

This module relies on a native C++ extension that is compiled during installation using your system's C++ compiler.

1. Prerequisites (for the current X11 backend on Debian/Ubuntu): Ensure you have a C++ compiler (g++) and development files for Python, X11, Xext (XShm), libjpeg-turbo, and libx264.

sudo apt-get update && \
sudo apt-get install -y \
  g++ \
  libjpeg-turbo8-dev \
  libx11-dev \
  libxfixes-dev \
  libxext-dev \
  libx264-dev \
  python3-dev

2. Install the Package: You can install directly from PyPI or from a local source clone.

   Option A: Install from PyPI

   pip install pixelflux

   Option B: Install from a local source directory

   # From the root of the project repository
   pip install .

   This command will use setuptools to directly compile the C++ extension (screen_capture_module.cpp) and install it alongside the Python code into your environment.

   Note: The current backend is designed and tested for Linux/X11 environments.

Usage

Basic Capture

Here is a basic example demonstrating how to use the pixelflux module to start capturing and process encoded stripes.

import time
from pixelflux import CaptureSettings, ScreenCapture, StripeCallback

# Define your Python callback function.
# This function will be called from a background thread for each encoded stripe.
def my_python_callback(result, user_data):
    """
    Callback function to process encoded stripes.
    `result` is a StripeEncodeResult object with the stripe's data.
    `user_data` is whatever object you passed to start_capture (or None).
    """
    if result.data:
        # result.type will be 1 for JPEG, 2 for H.264
        type_str = "H264" if result.type == 2 else "JPEG"

        print(
            f"Received {type_str} stripe: "
            f"frame_id={result.frame_id}, "
            f"y_start={result.stripe_y_start}, "
            f"height={result.stripe_height}, "
            f"size={len(result.data)} bytes"
        )
    
    # Memory is managed automatically. No need to free anything.

# 1. Configure capture settings
settings = CaptureSettings()
settings.capture_width = 1280
settings.capture_height = 720
settings.capture_x = 0
settings.capture_y = 0
settings.target_fps = 30.0

# Set output mode to H.264 (1)
settings.output_mode = 1
settings.h264_crf = 25 # H264 Constant Rate Factor (0-51, lower is better quality)

# 2. Instantiate the ScreenCapture module
module = ScreenCapture()

# 3. Create a StripeCallback handler object
# This object simply holds your Python function.
callback_handler = StripeCallback(my_python_callback)

try:
    # 4. Start the capture, passing the settings and callback handler.
    # The third argument is optional user_data to be passed to your callback.
    module.start_capture(settings, callback_handler, None)
    
    print("Capture started. Press Enter to stop...")
    input() # Keep the main thread alive while capture runs in the background.

finally:
    # 5. Stop the capture. This will block until the background thread has exited.
    module.stop_capture()
    print("Capture stopped.")

Capture Settings

The CaptureSettings class allows for detailed configuration of the capture process.

# All attributes of the CaptureSettings object are standard Python properties.
settings = CaptureSettings()

# Core Capture
settings.capture_width = 1920
settings.capture_height = 1080
settings.capture_x = 0
settings.capture_y = 0
settings.target_fps = 60.0
settings.capture_cursor = True

# Encoding Mode (0 for JPEG, 1 for H.264)
settings.output_mode = 1

# JPEG Quality Settings
settings.jpeg_quality = 75              # Quality for changed stripes (0-100)
settings.paint_over_jpeg_quality = 90   # Quality for static "paint-over" stripes (0-100)

# H.264 Quality Settings
settings.h264_crf = 23                  # CRF value (0-51, lower is better quality/higher bitrate)
settings.h264_fullcolor = False         # Use I444 (full color) instead of I420
settings.h264_fullframe = False         # Encode full frames instead of just changed stripes

# Change Detection & Optimization
settings.use_paint_over_quality = True  # Enable paint-over/IDR requests for static regions
settings.paint_over_trigger_frames = 15 # Frames of no motion to trigger paint-over
settings.damage_block_threshold = 10    # Consecutive changes to trigger "damaged" state
settings.damage_block_duration = 30     # Frames a stripe stays "damaged"

# Watermarking
settings.watermark_path = b"/path/to/your/watermark.png" # Must be bytes
settings.watermark_location_enum = 4 # 0:None, 1:TL, 2:TR, 3:BL, 4:BR, 5:Middle, 6:Animated

Stripe Callback and Data Structure

The start_capture function requires a StripeCallback object, which wraps your Python function. This function is invoked from a C++ background thread whenever an encoded stripe is ready.

Your callback function will receive two arguments:

1. result: A StripeEncodeResult object containing the stripe data.
2. user_data: The optional object you passed to start_capture.

The StripeEncodeResult object has the following read-only properties:

class StripeEncodeResult:
    # This is illustrative. You do not define this class.
    # You receive an instance of it in your callback.

    @property
    def type(self) -> int: ... # StripeDataType: 1 for JPEG, 2 for H.264

    @property
    def stripe_y_start(self) -> int: ...

    @property
    def stripe_height(self) -> int: ...

    @property
    def size(self) -> int: ... # The size of the data in bytes

    @property
    def data(self) -> bytes: ... # The encoded stripe data as a Python bytes object

    @property
    def frame_id(self) -> int: ... # Frame counter for this stripe

Memory Management: The memory for the stripe data is managed automatically. When the StripeEncodeResult object received by your callback is garbage-collected by Python, its internal C++ destructor is called, which frees the underlying data buffer. You do not need to do any manual memory management.

Features

• Efficient Pixel Capture: Leverages a native C++ module using XShm for optimized X11 screen capture performance.
• Stripe-Based Encoding (JPEG & H.264): Encodes captured frames into horizontal stripes, processed in parallel using a number of threads based on system core count. Each stripe is an independent data unit.
• Change Detection: Encodes only stripes that have changed (based on XXH3 hash comparison) since the last frame, significantly reducing processing load and bandwidth. This approach is inspired by VNC.
• Configurable Capture Region: Specify the exact X, Y, width, and height of the screen region to capture.
• Adjustable FPS, Quality, and Encoding Parameters: Control frame rate, JPEG quality (0-100), and H.264 CRF (0-51).
• Dynamic Quality Optimizations:
  • Paint-Over for Static Regions: After a stripe remains static for paint_over_trigger_frames, it is resent. For JPEG, this uses paint_over_jpeg_quality if use_paint_over_quality is true. For H.264, this triggers a request for an IDR frame for that stripe, ensuring a full refresh.
  • Adaptive Behavior for Highly Active Stripes (Damage Throttling):
    • Identifies stripes that change very frequently (exceeding damage_block_threshold updates).
    • For these "damaged" stripes, damage checks are done less frequently, saving resources on high motion.
    • For JPEG output, the quality of these frequently changing stripes dynamically adjusts (reducing slightly on change) and resets to higher base/paint-over quality after a cooldown period of damage_block_duration frames. This manages resources effectively for volatile content.
• Direct Callback Mechanism: Provides encoded stripe data, including a custom header, directly to your Python code for real-time processing or streaming.

Example: Real-time H.264 Streaming with WebSockets

A comprehensive example, screen_to_browser.py, is located in the example directory of this repository. This script demonstrates robust, real-time screen capture, H.264 encoding, and streaming via WebSockets. It sets up:

• An asyncio-based WebSocket server to stream encoded H.264 stripes.
• An HTTP server to serve a client-side HTML page for viewing the stream.
• The pixelflux module to perform the screen capture and encoding, with proper asynchronous shutdown logic to prevent deadlocks.

To run this example:

Note: This example assumes you are on a Linux host with a running X11 session and will only work from localhost unless HTTPS is added.

1. First, ensure you have the websockets library installed (it is a dependency for the example, not the library itself):

   pip install websockets

2. Navigate to the example directory within the repository:

   cd example

3. Execute the Python script:

   python3 screen_to_browser.py

4. Open your web browser and go to the URL indicated by the script's output (usually http://localhost:9001/index.html) to view the live stream.

License

This project is licensed under the Mozilla Public License Version 2.0. A copy of the MPL 2.0 can be found at https://mozilla.org/MPL/2.0/.