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Writing to video files

Prerequisites

Make sure ffmpeg is installed on your system.

Writing to video using render targets

fun main() = application {
    program {
        val videoWriter = VideoWriter.create().size(width, height).output("output.mp4").start()
        
        val videoTarget = renderTarget(width, height) {
            colorBuffer()
            depthBuffer()
        }
        

        var frame = 0
        extend {
            drawer.isolatedWithTarget(videoTarget) {
                clear(ColorRGBa.BLACK)
                rectangle(40.0 + frame, 40.0, 100.0, 100.0)
            }
            
            videoWriter.frame(videoTarget.colorBuffer(0))
            drawer.image(videoTarget.colorBuffer(0))
            frame++
            if (frame == 100) {
                videoWriter.stop()
                application.exit()
            }
        }
    }
}

The ScreenRecorder extension

A much simpler way of writing your program’s output to video is offered by the ScreenRecorder extension. The extension creates video files named after your Program class name plus the date. For example: MyProgram-2018-04-11-11.31.03.mp4. The video files are located in the video/ directory in your project.

To setup the screen recorder do the following:

fun main() = application {
    program {
        extend(ScreenRecorder())
        extend {// -- whatever you draw here ends up in the video
        }
    }
}

Toggle the ScreenRecorder on and off

By default the screen recorder extension adds video frames as long as the program runs. If you keep running the program again and again you will end up with a folder full of video files.

We can make it more flexible by letting the user start and pause the recorder, for instance by pressing the v key on the keyboard.

fun main() = application {
    program {
        // keep a reference to the recorder so we can start it and stop it.
        val recorder = ScreenRecorder().apply {
            outputToVideo = false
        }
        extend(recorder)
        extend {// -- draw things here
        }
        keyboard.keyDown.listen {
            when {
                it.key == KEY_ESCAPE -> program.application.exit()
                it.name == "v" -> {
                    recorder.outputToVideo = !recorder.outputToVideo
                    println(if (recorder.outputToVideo) "Recording" else "Paused")
                }
            }
        }
    }
}

Video formats

By default videos are recorded in h264 format with a .mp4 file extension, but animated gif or webp, png or tif sequences, prores and h265 are also available by enabling the orx-video-profiles extension.

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