How to read and write video files in Kotlin

How to read and write video files in Kotlin.

Here is a step-by-step tutorial on how to read and write video files in Kotlin:

Prerequisites

To follow along with this tutorial, make sure you have the following:

• Kotlin installed on your machine
• A video file (e.g., MP4, AVI, etc.) that you want to read or write

Reading Video Files

To read video files in Kotlin, we can make use of the OpenCV library. OpenCV is an open-source computer vision and machine learning software library that provides various functions for working with images and videos.

Step 1: Set Up OpenCV

Before we can use OpenCV in our Kotlin project, we need to set it up. Follow these steps to set up OpenCV:

1. Download the OpenCV library from the official website (https://opencv.org/releases/).
2. Extract the downloaded file to a location on your machine.
3. In your Kotlin project, create a new directory called "libs".
4. Copy the "opencv-xxx.jar" file from the extracted OpenCV folder to the "libs" directory.
5. Right-click on the "opencv-xxx.jar" file and select "Add as Library" to include it in your project.

Step 2: Read Video File

Now that OpenCV is set up, we can start reading video files. Here's an example code snippet to read a video file:

import org.opencv.core.Mat
import org.opencv.core.CvType
import org.opencv.core.CvType.CV_8UC3
import org.opencv.videoio.VideoCapture
import org.opencv.videoio.VideoWriter

fun main() {
    System.loadLibrary("opencv_java4")
    
    // Path to the video file
    val videoPath = "path/to/video/file.mp4"
    
    // Create a VideoCapture object to read the video file
    val videoCapture = VideoCapture(videoPath)
    
    // Check if the video file was successfully opened
    if (!videoCapture.isOpened) {
        println("Error opening video file")
        return
    }
    
    // Create a Mat object to store each frame of the video
    val frame = Mat()
    
    // Read and display each frame of the video
    while (videoCapture.read(frame)) {
        // Process each frame here (e.g., apply image filters, perform object detection, etc.)
        
        // Display the frame (optional)
        // imshow("Video", frame)
    }
    
    // Release the VideoCapture object and close the video file
    videoCapture.release()
}

In this example, we first load the OpenCV library using System.loadLibrary("opencv_java4"). Then, we specify the path to the video file that we want to read. Next, we create a VideoCapture object and pass the video file path to its constructor. We then check if the video file was successfully opened using the isOpened property.

Inside the while loop, we read each frame of the video using the read() method of the VideoCapture object. The frame is stored in a Mat object, which is a multi-dimensional array that represents an image or video frame. You can perform any processing you want on each frame inside the loop.

After processing all frames, we release the VideoCapture object using the release() method to free up system resources.

Writing Video Files

To write video files in Kotlin, we can again use the OpenCV library. Here's an example code snippet to write a video file:

import org.opencv.core.Mat
import org.opencv.videoio.VideoCapture
import org.opencv.videoio.VideoWriter

fun main() {
    System.loadLibrary("opencv_java4")
    
    // Path to the input video file
    val inputVideoPath = "path/to/input/video/file.mp4"
    
    // Create a VideoCapture object to read the input video file
    val videoCapture = VideoCapture(inputVideoPath)
    
    // Check if the input video file was successfully opened
    if (!videoCapture.isOpened) {
        println("Error opening input video file")
        return
    }
    
    // Get the input video's properties
    val width = videoCapture.get(Videoio.CAP_PROP_FRAME_WIDTH)
    val height = videoCapture.get(Videoio.CAP_PROP_FRAME_HEIGHT)
    val fps = videoCapture.get(Videoio.CAP_PROP_FPS)
    
    // Path to the output video file
    val outputVideoPath = "path/to/output/video/file.mp4"
    
    // Create a VideoWriter object to write the output video file
    val videoWriter = VideoWriter(outputVideoPath, VideoWriter.fourcc('X', 'V', 'I', 'D'), fps, Size(width, height))
    
    // Check if the output video file was successfully opened
    if (!videoWriter.isOpened) {
        println("Error opening output video file")
        return
    }
    
    // Create a Mat object to store each frame of the video
    val frame = Mat()
    
    // Read and write each frame of the video
    while (videoCapture.read(frame)) {
        // Process each frame here (e.g., apply image filters, perform object detection, etc.)
        
        // Write the processed frame to the output video file
        videoWriter.write(frame)
    }
    
    // Release the VideoCapture and VideoWriter objects
    videoCapture.release()
    videoWriter.release()
}

In this example, we first load the OpenCV library using System.loadLibrary("opencv_java4"). Then, we specify the path to the input video file that we want to write. We create a VideoCapture object to read the input video file and check if it was successfully opened.

Next, we get the properties of the input video (width, height, and frames per second) using the get() method of the VideoCapture object.

We then specify the path to the output video file that we want to write. We create a VideoWriter object and pass the output video file path, four-character code for the video codec (e.g., XVID), frames per second, and the size of each frame. Again, we check if the output video file was successfully opened.

Inside the while loop, we read each frame of the input video using the read() method of the VideoCapture object. The frame is stored in a Mat object, and you can perform any processing you want on each frame inside the loop.

After processing each frame, we write it to the output video file using the write() method of the VideoWriter object.

Finally, we release the VideoCapture and VideoWriter objects to free up system resources.

That's it! You have learned how to read and write video files in Kotlin using the OpenCV library.