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@bellbind
Last active Sep 22, 2020
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[linux][v4l2][libjpeg][c99]example for capturing from UVC webcam (on beaglebone black)
/*
* capturing from UVC cam
* requires: libjpeg-dev
* build: gcc -std=c99 capture.c -ljpeg -o capture
*/
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <asm/types.h>
#include <linux/videodev2.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>
#include <jpeglib.h>
void quit(const char * msg)
{
fprintf(stderr, "[%s] %d: %s\n", msg, errno, strerror(errno));
exit(EXIT_FAILURE);
}
int xioctl(int fd, int request, void* arg)
{
for (int i = 0; i < 100; i++) {
int r = ioctl(fd, request, arg);
if (r != -1 || errno != EINTR) return r;
}
return -1;
}
typedef struct {
uint8_t* start;
size_t length;
} buffer_t;
typedef struct {
int fd;
uint32_t width;
uint32_t height;
size_t buffer_count;
buffer_t* buffers;
buffer_t head;
} camera_t;
camera_t* camera_open(const char * device, uint32_t width, uint32_t height)
{
int fd = open(device, O_RDWR | O_NONBLOCK, 0);
if (fd == -1) quit("open");
camera_t* camera = malloc(sizeof (camera_t));
camera->fd = fd;
camera->width = width;
camera->height = height;
camera->buffer_count = 0;
camera->buffers = NULL;
camera->head.length = 0;
camera->head.start = NULL;
return camera;
}
void camera_init(camera_t* camera) {
struct v4l2_capability cap;
if (xioctl(camera->fd, VIDIOC_QUERYCAP, &cap) == -1) quit("VIDIOC_QUERYCAP");
if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) quit("no capture");
if (!(cap.capabilities & V4L2_CAP_STREAMING)) quit("no streaming");
struct v4l2_cropcap cropcap;
memset(&cropcap, 0, sizeof cropcap);
cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (xioctl(camera->fd, VIDIOC_CROPCAP, &cropcap) == 0) {
struct v4l2_crop crop;
crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
crop.c = cropcap.defrect;
if (xioctl(camera->fd, VIDIOC_S_CROP, &crop) == -1) {
// cropping not supported
}
}
struct v4l2_format format;
memset(&format, 0, sizeof format);
format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
format.fmt.pix.width = camera->width;
format.fmt.pix.height = camera->height;
format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
format.fmt.pix.field = V4L2_FIELD_NONE;
if (xioctl(camera->fd, VIDIOC_S_FMT, &format) == -1) quit("VIDIOC_S_FMT");
struct v4l2_requestbuffers req;
memset(&req, 0, sizeof req);
req.count = 4;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if (xioctl(camera->fd, VIDIOC_REQBUFS, &req) == -1) quit("VIDIOC_REQBUFS");
camera->buffer_count = req.count;
camera->buffers = calloc(req.count, sizeof (buffer_t));
size_t buf_max = 0;
for (size_t i = 0; i < camera->buffer_count; i++) {
struct v4l2_buffer buf;
memset(&buf, 0, sizeof buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if (xioctl(camera->fd, VIDIOC_QUERYBUF, &buf) == -1)
quit("VIDIOC_QUERYBUF");
if (buf.length > buf_max) buf_max = buf.length;
camera->buffers[i].length = buf.length;
camera->buffers[i].start =
mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED,
camera->fd, buf.m.offset);
if (camera->buffers[i].start == MAP_FAILED) quit("mmap");
}
camera->head.start = malloc(buf_max);
}
void camera_start(camera_t* camera)
{
for (size_t i = 0; i < camera->buffer_count; i++) {
struct v4l2_buffer buf;
memset(&buf, 0, sizeof buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if (xioctl(camera->fd, VIDIOC_QBUF, &buf) == -1) quit("VIDIOC_QBUF");
}
enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (xioctl(camera->fd, VIDIOC_STREAMON, &type) == -1)
quit("VIDIOC_STREAMON");
}
void camera_stop(camera_t* camera)
{
enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (xioctl(camera->fd, VIDIOC_STREAMOFF, &type) == -1)
quit("VIDIOC_STREAMOFF");
}
void camera_finish(camera_t* camera)
{
for (size_t i = 0; i < camera->buffer_count; i++) {
munmap(camera->buffers[i].start, camera->buffers[i].length);
}
free(camera->buffers);
camera->buffer_count = 0;
camera->buffers = NULL;
free(camera->head.start);
camera->head.length = 0;
camera->head.start = NULL;
}
void camera_close(camera_t* camera)
{
if (close(camera->fd) == -1) quit("close");
free(camera);
}
int camera_capture(camera_t* camera)
{
struct v4l2_buffer buf;
memset(&buf, 0, sizeof buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
if (xioctl(camera->fd, VIDIOC_DQBUF, &buf) == -1) return FALSE;
memcpy(camera->head.start, camera->buffers[buf.index].start, buf.bytesused);
camera->head.length = buf.bytesused;
if (xioctl(camera->fd, VIDIOC_QBUF, &buf) == -1) return FALSE;
return TRUE;
}
int camera_frame(camera_t* camera, struct timeval timeout) {
fd_set fds;
FD_ZERO(&fds);
FD_SET(camera->fd, &fds);
int r = select(camera->fd + 1, &fds, 0, 0, &timeout);
if (r == -1) quit("select");
if (r == 0) return FALSE;
return camera_capture(camera);
}
void
jpeg(FILE* dest, uint8_t* rgb, uint32_t width, uint32_t height, int quality)
{
JSAMPARRAY image;
image = calloc(height, sizeof (JSAMPROW));
for (size_t i = 0; i < height; i++) {
image[i] = calloc(width * 3, sizeof (JSAMPLE));
for (size_t j = 0; j < width; j++) {
image[i][j * 3 + 0] = rgb[(i * width + j) * 3 + 0];
image[i][j * 3 + 1] = rgb[(i * width + j) * 3 + 1];
image[i][j * 3 + 2] = rgb[(i * width + j) * 3 + 2];
}
}
struct jpeg_compress_struct compress;
struct jpeg_error_mgr error;
compress.err = jpeg_std_error(&error);
jpeg_create_compress(&compress);
jpeg_stdio_dest(&compress, dest);
compress.image_width = width;
compress.image_height = height;
compress.input_components = 3;
compress.in_color_space = JCS_RGB;
jpeg_set_defaults(&compress);
jpeg_set_quality(&compress, quality, TRUE);
jpeg_start_compress(&compress, TRUE);
jpeg_write_scanlines(&compress, image, height);
jpeg_finish_compress(&compress);
jpeg_destroy_compress(&compress);
for (size_t i = 0; i < height; i++) {
free(image[i]);
}
free(image);
}
int minmax(int min, int v, int max)
{
return (v < min) ? min : (max < v) ? max : v;
}
uint8_t* yuyv2rgb(uint8_t* yuyv, uint32_t width, uint32_t height)
{
uint8_t* rgb = calloc(width * height * 3, sizeof (uint8_t));
for (size_t i = 0; i < height; i++) {
for (size_t j = 0; j < width; j += 2) {
size_t index = i * width + j;
int y0 = yuyv[index * 2 + 0] << 8;
int u = yuyv[index * 2 + 1] - 128;
int y1 = yuyv[index * 2 + 2] << 8;
int v = yuyv[index * 2 + 3] - 128;
rgb[index * 3 + 0] = minmax(0, (y0 + 359 * v) >> 8, 255);
rgb[index * 3 + 1] = minmax(0, (y0 + 88 * v - 183 * u) >> 8, 255);
rgb[index * 3 + 2] = minmax(0, (y0 + 454 * u) >> 8, 255);
rgb[index * 3 + 3] = minmax(0, (y1 + 359 * v) >> 8, 255);
rgb[index * 3 + 4] = minmax(0, (y1 + 88 * v - 183 * u) >> 8, 255);
rgb[index * 3 + 5] = minmax(0, (y1 + 454 * u) >> 8, 255);
}
}
return rgb;
}
int main()
{
camera_t* camera = camera_open("/dev/video0", 352, 288);
camera_init(camera);
camera_start(camera);
struct timeval timeout;
timeout.tv_sec = 1;
timeout.tv_usec = 0;
/* skip 5 frames for booting a cam */
for (int i = 0; i < 5; i++) {
camera_frame(camera, timeout);
}
camera_frame(camera, timeout);
unsigned char* rgb =
yuyv2rgb(camera->head.start, camera->width, camera->height);
FILE* out = fopen("result.jpg", "w");
jpeg(out, rgb, camera->width, camera->height, 100);
fclose(out);
free(rgb);
camera_stop(camera);
camera_finish(camera);
camera_close(camera);
return 0;
}
@qianfan-Zhao

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@qianfan-Zhao qianfan-Zhao commented Aug 18, 2017

HI:
I am testing this code on my device, but after 6 seconds passed, i got a pure black picture, seems camera not work.
But my camera can work in win10 or winxp. Can you help me solve this problem? thanks

@escrowdis

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@escrowdis escrowdis commented Aug 31, 2017

@zhaozhongchen Maybe you should check your camera's output size of image
camera_t* camera = camera_open("/dev/video0", <height>, <width>);

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