V4L2

V4L2 definitions for Go.

Copyright and Licensing

Copyright (c) 2020 Peter Hagelund

This software is licensed under the MIT License

See LICENSE.txt

Installing

go get -u github.com/peterhagelund/go-v4l2

Using modules

In go.mod:

require "github.com/peterhagelund/go-v4l2" v0.2.6

Using

import (
	"bytes"
	"fmt"
	"image"
	"image/jpeg"
	"io/ioutil"
	"os"
	"unsafe"

	"github.com/peterhagelund/go-v4l2"
	"golang.org/x/sys/unix"
)

...

fd, err := unix.Open("/dev/video0", unix.O_RDWR, 0)
if err != nil {
	panic(err)
}
defer unix.Close(fd)
capability, err := v4l2.QueryCapabilities(fd)
if err != nil {
	panic(err)
}
fmt.Printf("Driver....: %s\n", v4l2.BytesToString(capability.Driver[:]))
fmt.Printf("Card......: %s\n", v4l2.BytesToString(capability.Card[:]))
fmt.Printf("BusInfo...: %s\n", v4l2.BytesToString(capability.BusInfo[:]))
fmtDescs, err := v4l2.EnumFormats(fd, v4l2.BufTypeVideoCapture)
if err != nil {
	panic(err)
}
fmt.Printf("Formats:\n")
for _, fmtDesc := range fmtDescs {
	fmt.Printf("\tFormat...: %s\n", v4l2.BytesToString(fmtDesc.Description[:]))
}
fmt.Printf("Frame sizes for JPEG:\n")
frameSizeEnums, err := v4l2.EnumFrameSizes(fd, v4l2.PixFmtJPEG)
if err != nil {
	panic(err)
}
for _, frameSizeEnum := range frameSizeEnums {
	if frameSizeEnum.Type == v4l2.FrmSizeTypeDiscrete {
		discrete := (*v4l2.FrameSizeDiscrete)(unsafe.Pointer(&frameSizeEnum.M))
		fmt.Printf("\tDiscrete:\n")
		fmt.Printf("\t\tWidth....: %d\n", discrete.Width)
		fmt.Printf("\t\tHeight...: %d\n", discrete.Height)
	} else {
		if frameSizeEnum.Type == v4l2.FrmSizeTypeStepwise {
			fmt.Printf("\tStepwise:\n")
		} else {
			fmt.Printf("\tContinuous:\n")
		}
		stepwise := (*v4l2.FrameSizeStepwise)(unsafe.Pointer(&frameSizeEnum.M))
		fmt.Printf("\t\tMinWidth.....: %d\n", stepwise.MinWidth)
		fmt.Printf("\t\tMaxWidth.....: %d\n", stepwise.MaxWidth)
		fmt.Printf("\t\tStepWidth....: %d\n", stepwise.StepWidth)
		fmt.Printf("\t\tMinHeight....: %d\n", stepwise.MinHeight)
		fmt.Printf("\t\tMaxHeight....: %d\n", stepwise.MaxHeight)
		fmt.Printf("\t\tStepHeight...: %d\n", stepwise.StepHeight)
	}
}
width, height, err := v4l2.SetFormat(fd, v4l2.BufTypeVideoCapture, v4l2.PixFmtJPEG, 1024, 768)
if err != nil {
	panic(err)
}
fmt.Printf("Frame size:\n")
fmt.Printf("\tWidth....: %d\n", width)
fmt.Printf("\tHeight...: %d\n", height)
count, err := v4l2.RequestDriverBuffers(fd, 4, v4l2.BufTypeVideoCapture, v4l2.MemoryMmap)
if err != nil {
	panic(err)
}
defer v4l2.RequestDriverBuffers(fd, 0, v4l2.BufTypeVideoCapture, v4l2.MemoryMmap)
fmt.Printf("Driver buffer count...: %d\n", count)
buffers, err := v4l2.MmapBuffers(fd, count, v4l2.BufTypeVideoCapture)
if err != nil {
	panic(err)
}
defer v4l2.MunmapBuffers(buffers)
if err := v4l2.StreamOn(fd, v4l2.BufTypeVideoCapture); err != nil {
	panic(err)
}
defer v4l2.StreamOff(fd, v4l2.BufTypeVideoCapture)
frame, err := v4l2.GrabFrame(fd, v4l2.BufTypeVideoCapture, v4l2.MemoryMmap, buffers)
if err != nil {
	panic(err)
}
if err := ioutil.WriteFile("test1.jpeg", frame, 0644); err != nil {
	panic(err)
}
buffer := bytes.NewBuffer(frame)
img, name, err := image.Decode(buffer)
if err != nil {
	panic(err)
}
fmt.Printf("Image:\n")
fmt.Printf("\tName.....: %s\n", name)
fmt.Printf("\tWidth....: %d\n", img.Bounds().Dx())
fmt.Printf("\tHeight...: %d\n", img.Bounds().Dy())
file, err := os.Create("test2.jpeg")
if err != nil {
	panic(err)
}
err = jpeg.Encode(file, img, nil)
if err != nil {
	panic(err)
}

On a Raspberry Pi model 3B, output would be:

Driver....: bm2835 mmal
Card......: mmal service 16.1
BusInfo...: platform:bcm2835-v4l2
Formats:
        Format...: Planar YUV 4:2:0
        Format...: YUYV 4:2:2
        Format...: 24-bit RGB 8-8-8
        Format...: JFIF JPEG
        Format...: H.264
        Format...: Motion-JPEG
        Format...: YVYU 4:2:2
        Format...: VYUY 4:2:2
        Format...: UYVY 4:2:2
        Format...: Y/CbCr 4:2:0
        Format...: 24-bit BGR 8-8-8
        Format...: Planar YVU 4:2:0
        Format...: Y/CrCb 4:2:0
        Format...: 32-bit BGRA/X 8-8-8-8
Frame sizes for JPEG:
        Stepwise:
                MinWidth.....: 32
                MaxWidth.....: 3280
                StepWidth....: 2
                MinHeight....: 32
                MaxHeight....: 2464
                StepHeight...: 2
Frame size:
        Width....: 1024
        Height...: 768
Driver buffer count...: 4
Image:
        Name.....: jpeg
        Width....: 1024
        Height...: 768

ls -l *.jpeg
-rw-r--r-- 1 pi pi 270690 Apr  9 08:39 test1.jpeg
-rw-r--r-- 1 pi pi  61599 Apr  9 08:39 test2.jpeg