# Implementing Custom Zoom Effects with OnVideoFrameBuffer in .NET

Video Capture SDK .Net Video Edit SDK .Net Media Player SDK .Net

Implementing custom zoom effects in video applications is a common requirement for developers working with video processing. This guide explains how to manually create zoom functionality in your .NET video applications using the OnVideoFrameBuffer event. This technique works across multiple SDK platforms, including Video Capture, Media Player, and Video Edit SDKs.

The OnVideoFrameBuffer event is a powerful feature that gives developers direct access to video frame data during playback or processing. By handling this event, you can:

• Access raw frame data in real-time
• Apply custom modifications to individual frames
• Implement visual effects like zooming, rotation, or color adjustments
• Control video quality and performance

The process of implementing a zoom effect involves several key steps:

1. Allocating memory for temporary buffers
2. Handling the OnVideoFrameBuffer event
3. Applying the zoom transformation to each frame
4. Managing memory to prevent leaks

Let's break down each of these steps with detailed explanations.

When working with video frames, proper memory management is critical. You'll need to allocate sufficient memory to handle frame data and temporary processing buffers.

private IntPtr tempBuffer = IntPtr.Zero;
IntPtr tmpZoomFrameBuffer = IntPtr.Zero;
private int tmpZoomFrameBufferSize = 0;

These fields serve the following purposes:

• tempBuffer: Stores the processed frame data
• tmpZoomFrameBuffer: Holds the intermediary zoom calculation results
• tmpZoomFrameBufferSize: Tracks the required size for the zoom buffer

Below is a complete implementation of the zoom effect using the OnVideoFrameBuffer event in a Media Player SDK .NET application:

private IntPtr tempBuffer = IntPtr.Zero;
IntPtr tmpZoomFrameBuffer = IntPtr.Zero;
private int tmpZoomFrameBufferSize = 0;

private void MediaPlayer1_OnVideoFrameBuffer(object sender, VideoFrameBufferEventArgs e)
{
    // Initialize the temporary buffer if it hasn't been created yet
    if (tempBuffer == IntPtr.Zero)
    {
        tempBuffer = Marshal.AllocCoTaskMem(e.Frame.DataSize);
    }

    // Set the zoom factor (2.0 = 200% zoom)
    const double zoom = 2.0;
    
    // Apply the zoom effect using the FastImageProcessing utility
    FastImageProcessing.EffectZoom(
        e.Frame.Data,           // Source frame data
        e.Frame.Width,          // Frame width
        e.Frame.Height,         // Frame height 
        tempBuffer,             // Output buffer
        zoom,                   // Horizontal zoom factor
        zoom,                   // Vertical zoom factor
        0,                      // Center X coordinate (0 = center)
        0,                      // Center Y coordinate (0 = center)
        tmpZoomFrameBuffer,     // Intermediate buffer
        ref tmpZoomFrameBufferSize); // Buffer size reference
    
    // Allocate the zoom frame buffer if needed and return to process in next frame
    if (tmpZoomFrameBufferSize > 0 && tmpZoomFrameBuffer == IntPtr.Zero)
    {
        tmpZoomFrameBuffer = Marshal.AllocCoTaskMem(tmpZoomFrameBufferSize);
        return;
    }

    // Copy the processed data back to the frame buffer
    FastImageProcessing.CopyMemory(tempBuffer, e.Frame.Data, e.Frame.DataSize);
}

The code above uses a fixed zoom factor of 2.0 (200%), but you can modify this to create various zoom effects:

You can implement user-controlled zoom by replacing the constant zoom value with a variable:

// Replace this:
const double zoom = 2.0;

// With something like this:
double zoom = this.userZoomSlider.Value; // Get zoom value from UI control

The EffectZoom method accepts X and Y coordinates to set the center point of the zoom. Setting these to non-zero values allows you to focus the zoom on specific areas:

// Zoom centered on the top-right quadrant
FastImageProcessing.EffectZoom(
    e.Frame.Data,
    e.Frame.Width,
    e.Frame.Height, 
    tempBuffer, 
    zoom, 
    zoom, 
    e.Frame.Width / 4,  // X offset from center 
    -e.Frame.Height / 4, // Y offset from center
    tmpZoomFrameBuffer,
    ref tmpZoomFrameBufferSize);

When implementing custom video effects like zooming, consider these performance tips:

1. Memory Management: Always free allocated memory when your application closes to prevent leaks
2. Buffer Reuse: Reuse buffers when possible rather than reallocating for each frame
3. Processing Time: Keep processing time minimal to maintain smooth video playback
4. Resolution Impact: Higher resolution videos require more processing power for real-time effects

To properly clean up resources when your application closes, implement a cleanup method:

private void CleanupZoomResources()
{
    if (tempBuffer != IntPtr.Zero)
    {
        Marshal.FreeCoTaskMem(tempBuffer);
        tempBuffer = IntPtr.Zero;
    }

    if (tmpZoomFrameBuffer != IntPtr.Zero)
    {
        Marshal.FreeCoTaskMem(tmpZoomFrameBuffer);
        tmpZoomFrameBuffer = IntPtr.Zero;
    }
}

Call this method when your form or application closes to prevent memory leaks.

When implementing the zoom effect, you might encounter these issues:

1. Distorted Image: Check that your zoom factors for width and height are equal for uniform scaling
2. Blank Frames: Ensure proper memory allocation and buffer sizes
3. Poor Performance: Consider reducing the frame processing complexity or the video resolution
4. Memory Errors: Verify that all memory is properly allocated and freed

Implementing custom zoom effects using the OnVideoFrameBuffer event gives you precise control over video appearance in your .NET applications. By following the techniques outlined in this guide, you can create sophisticated zoom functionality that enhances the user experience in your video applications.

Remember to properly manage memory resources and optimize for performance to ensure smooth playback with your custom effects.

Visit our GitHub page to get more code samples.