go4vl

README

go4vl

A Go centric abstraction of the library for Video for Linux 2 (v4l2) user API.

---

The go4vl project is for working with the Video for Linux 2 API for real-time video. It hides all the complexities of working with V4L2 and provides idiomatic Go types, like channels, to consume and process captured video frames.

This project is designed to work with Linux and the Linux Video API only. It is NOT meant to be a portable/cross-platform package.

Features

• Capture and control video data from your Go programs
• Idiomatic Go types such as channels to access and stream video data
• Exposes device enumeration and information
• Provides device capture control
• Access to video format information
• Streaming users zero-copy IO using memory mapped buffers

Compilation Requirements

• Go compiler/tools
• Kernel minimum v5.10.x
• A locally configured C compiler (i.e. gcc)

All examples have been tested using a Raspberry PI 3, running 32-bit Raspberry PI OS. The package should work with no problem on your 64-bit Linux OS.

Getting started

System upgrade

To avoid issues with old header files on your machine, upgrade your system to pull down the latest OS packages with something similar to the following (follow directions for your system for proper upgrade):

sudo apt update
sudo apt full-upgrade

Install the build-essential package to install required C compilers:

sudo apt install build-essential

Using the go4vl package

To include go4vl in your own code, go get the package:

go get github.com/vladimirvivien/go4vl/v4l2

Video capture example

The following is a simple example that captures video data from an attached camera device to and saves the captured frames as JPEG files.

The example assumes the attached device supports JPEG (MJPEG) output format inherently.

func main() {
	devName := "/dev/video0"
	flag.StringVar(&devName, "d", devName, "device name (path)")
	flag.Parse()

	// open device
	device, err := device.Open(
		devName,
		device.WithPixFormat(v4l2.PixFormat{PixelFormat: v4l2.PixelFmtMPEG, Width: 640, Height: 480}),
	)
	if err != nil {
		log.Fatalf("failed to open device: %s", err)
	}
	defer device.Close()

	// start stream with cancellable context
	ctx, stop := context.WithCancel(context.TODO())
	if err := device.Start(ctx); err != nil {
		log.Fatalf("failed to start stream: %s", err)
	}

	// process frames from capture channel
	totalFrames := 10
	count := 0
	log.Printf("Capturing %d frames...", totalFrames)

	for frame := range device.GetOutput() {
		fileName := fmt.Sprintf("capture_%d.jpg", count)
		file, err := os.Create(fileName)
		if err != nil {
			log.Printf("failed to create file %s: %s", fileName, err)
			continue
		}
		if _, err := file.Write(frame); err != nil {
			log.Printf("failed to write file %s: %s", fileName, err)
			continue
		}
		log.Printf("Saved file: %s", fileName)
		if err := file.Close(); err != nil {
			log.Printf("failed to close file %s: %s", fileName, err)
		}
		count++
		if count >= totalFrames {
			break
		}
	}

	stop() // stop capture
	fmt.Println("Done.")
}

Read a detail walk-through about this example here.

Other examples

The ./examples directory contains additional examples including:

• device_info - queries and prints video device information
• webcam - uses the v4l2 package to create a simple webcam that streams images from an attached camera accessible via a web page.

Roadmap

The main goal is to port as many functionalities as possible so that adopters can use Go to create cool video-based tools on platforms such as the Raspberry Pi.