Crop Video

How to crop a 16:9 video to a 4:3 video.

Source Video

For a source video we use the MP4 file from the TED talk video What’s the next window into our universe? by Andrew Connolly. The original video format is Wide 480p or 16:9, 854 x 480.

Complete Program

This code takes an MP4 file with 16:9 480p (854x480) video and AAC audio, and crops the video to 4:3 640x480. The audio stream is copied from the source as is.

using PrimoSoftware.AVBlocks;
using System.Collections.Generic;

namespace CropVideo
{
    class Program
    {
        static void Main(string[] args)
        {
            Library.Initialize();

            // start with two identical input and output configuration
            var inputInfo = new MediaInfo() {
                InputFile = "AndrewConnolly_2014.mp4"
            };

            var outputInfo = new MediaInfo() {
                InputFile = "AndrewConnolly_2014.mp4"
            };

            if (inputInfo.Load() && outputInfo.Load()) {
                
                // create input socket
                var inputSocket = MediaSocket.FromMediaInfo(inputInfo);

                // create output socket
                var outputSocket = MediaSocket.FromMediaInfo(outputInfo);
                outputSocket.File = "AndrewConnolly_2014_640x480.mp4";

                // set the new frame width and height to 640 x 480
                var outVideoStream = outputSocket.Pins[0].StreamInfo as VideoStreamInfo;
                outVideoStream.FrameWidth = 640;
                outVideoStream.FrameHeight = 480;

                // set the display ratio to 4:3
                outVideoStream.DisplayRatioWidth = 4;
                outVideoStream.DisplayRatioHeight = 3;

                // set Crop.Left and Crop.Right 
                var outVideoPin = outputSocket.Pins[0];
                outVideoPin.Params = new Dictionary<string, object>() {
                    // The input video is 854x480. 
                    // To make it 640x480 we have to cut (854 - 640) / 2 pixels from each side.
                    { Param.Video.Crop.Left, (854 - 640) / 2 },
                    { Param.Video.Crop.Right, (854 - 640) / 2 } 
                };

                // create and run a transcoder
                using (var transcoder = new Transcoder()) {
                    transcoder.Inputs.Add(inputSocket);
                    transcoder.Outputs.Add(outputSocket);

                    // process
                    if (transcoder.Open())
                    {
                        transcoder.Run();
                        transcoder.Close();
                    }
                }
            }

            Library.Shutdown();
        }
    }
}

How to run

Follow the steps to create a C# console application in Visual Studio but in Program.cs use the code from this article.

Download the AndrewConnolly_2014.mp4 MPEG4 file from the Internet Archive and save it in bin/x64/Debug/net6.0 under the project’s directory.

Run the application in Visual Studio. Wait a few seconds for the Transcoder to finish. The converted file AndrewConnolly_2014_640x480.mp4 will be in the bin/x64/Debug/net6.0 directory.