是否有任何c库可以从linux上的网络摄像头获取视频？
答案 0 :(得分：13)
我们很多人使用OpenCV（跨平台的计算机视觉库，目前在v2.1上）
以下代码段从相机抓取帧，将它们转换为灰度并在屏幕上显示：
#include <stdio.h>
#include "cv.h"
#include "highgui.h"
typedef IplImage* (*callback_prototype)(IplImage*);
/*
* make_it_gray: custom callback to convert a colored frame to its grayscale version.
* Remember that you must deallocate the returned IplImage* yourself after calling this function.
*/
IplImage* make_it_gray(IplImage* frame)
{
// Allocate space for a new image
IplImage* gray_frame = 0;
gray_frame = cvCreateImage(cvSize(frame->width, frame->height), frame->depth, 1);
if (!gray_frame)
{
fprintf(stderr, "!!! cvCreateImage failed!\n" );
return NULL;
}
cvCvtColor(frame, gray_frame, CV_RGB2GRAY);
return gray_frame;
}
/*
* process_video: retrieves frames from camera and executes a callback to do individual frame processing.
* Keep in mind that if your callback takes too much time to execute, you might loose a few frames from
* the camera.
*/
void process_video(callback_prototype custom_cb)
{
// Initialize camera
CvCapture *capture = 0;
capture = cvCaptureFromCAM(-1);
if (!capture)
{
fprintf(stderr, "!!! Cannot open initialize webcam!\n" );
return;
}
// Create a window for the video
cvNamedWindow("result", CV_WINDOW_AUTOSIZE);
IplImage* frame = 0;
char key = 0;
while (key != 27) // ESC
{
frame = cvQueryFrame(capture);
if(!frame)
{
fprintf( stderr, "!!! cvQueryFrame failed!\n" );
break;
}
// Execute callback on each frame
IplImage* processed_frame = (*custom_cb)(frame);
// Display processed frame
cvShowImage("result", processed_frame);
// Release resources
cvReleaseImage(&processed_frame);
// Exit when user press ESC
key = cvWaitKey(10);
}
// Free memory
cvDestroyWindow("result");
cvReleaseCapture(&capture);
}
int main( int argc, char **argv )
{
process_video(make_it_gray);
return 0;
}
答案 1 :(得分：7)
v4l2官方示例
你得到了什么：
./v4l2grab：捕获一些快照到文件outNNN.ppm ./v4l2gl：使用OpenGL纹理（即时渲染，嘿！）和原始X11窗口（以及GLUT的gluLookAt进行实时显示视频直播）。如何在Ubuntu 16.04上获取它：
sudo apt-get install libv4l-dev
sudo apt-get build-dep libv4l-dev
git clone git://linuxtv.org/v4l-utils.git
cd v4l-utils
# Matching the installed version of dpkg -s libv4l-dev
git checkout v4l-utils-1.10.0
./bootstrap.sh
./configure
make
# TODO: fails halfway, but it does not matter for us now.
cd contrib/tests
make
在Git树之外使用这些示例也很容易，只需将它们复制出来，使相对包含""绝对<>，然后删除config.h。我在https://github.com/cirosantilli/cpp-cheat/tree/09fe73d248f7da2e9c9f3eff2520a143c259f4a6/v4l2
文档中的最小示例
文档4.9.0在https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/v4l2grab-example.html包含./v4l2grab的最小版本。我需要对其进行最低限度的修补，然后我将修补程序发送到http://www.spinics.net/lists/linux-media/（他们的文档在Linux内核树中以第一个整齐的方式存在），在那里它被彻底忽略了。
用法：
gcc v4l2grab.c -lv4l2
./a.out
补丁代码：
/* V4L2 video picture grabber
Copyright (C) 2009 Mauro Carvalho Chehab <mchehab@infradead.org>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <linux/videodev2.h>
#include <libv4l2.h>
#define CLEAR(x) memset(&(x), 0, sizeof(x))
struct buffer {
void *start;
size_t length;
};
static void xioctl(int fh, int request, void *arg)
{
int r;
do {
r = v4l2_ioctl(fh, request, arg);
} while (r == -1 && ((errno == EINTR) || (errno == EAGAIN)));
if (r == -1) {
fprintf(stderr, "error %d, %s\\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
}
int main(int argc, char **argv)
{
struct v4l2_format fmt;
struct v4l2_buffer buf;
struct v4l2_requestbuffers req;
enum v4l2_buf_type type;
fd_set fds;
struct timeval tv;
int r, fd = -1;
unsigned int i, n_buffers;
char *dev_name = "/dev/video0";
char out_name[256];
FILE *fout;
struct buffer *buffers;
fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
if (fd < 0) {
perror("Cannot open device");
exit(EXIT_FAILURE);
}
CLEAR(fmt);
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = 640;
fmt.fmt.pix.height = 480;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
xioctl(fd, VIDIOC_S_FMT, &fmt);
if (fmt.fmt.pix.pixelformat != V4L2_PIX_FMT_RGB24) {
printf("Libv4l didn't accept RGB24 format. Can't proceed.\\n");
exit(EXIT_FAILURE);
}
if ((fmt.fmt.pix.width != 640) || (fmt.fmt.pix.height != 480))
printf("Warning: driver is sending image at %dx%d\\n",
fmt.fmt.pix.width, fmt.fmt.pix.height);
CLEAR(req);
req.count = 2;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
xioctl(fd, VIDIOC_REQBUFS, &req);
buffers = calloc(req.count, sizeof(*buffers));
for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = n_buffers;
xioctl(fd, VIDIOC_QUERYBUF, &buf);
buffers[n_buffers].length = buf.length;
buffers[n_buffers].start = v4l2_mmap(NULL, buf.length,
PROT_READ | PROT_WRITE, MAP_SHARED,
fd, buf.m.offset);
if (MAP_FAILED == buffers[n_buffers].start) {
perror("mmap");
exit(EXIT_FAILURE);
}
}
for (i = 0; i < n_buffers; ++i) {
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
xioctl(fd, VIDIOC_QBUF, &buf);
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
xioctl(fd, VIDIOC_STREAMON, &type);
for (i = 0; i < 20; i++) {
do {
FD_ZERO(&fds);
FD_SET(fd, &fds);
/* Timeout. */
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select(fd + 1, &fds, NULL, NULL, &tv);
} while ((r == -1 && (errno = EINTR)));
if (r == -1) {
perror("select");
return errno;
}
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
xioctl(fd, VIDIOC_DQBUF, &buf);
sprintf(out_name, "out%03d.ppm", i);
fout = fopen(out_name, "w");
if (!fout) {
perror("Cannot open image");
exit(EXIT_FAILURE);
}
fprintf(fout, "P6\n%d %d 255\n",
fmt.fmt.pix.width, fmt.fmt.pix.height);
fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
fclose(fout);
xioctl(fd, VIDIOC_QBUF, &buf);
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
xioctl(fd, VIDIOC_STREAMOFF, &type);
for (i = 0; i < n_buffers; ++i)
v4l2_munmap(buffers[i].start, buffers[i].length);
v4l2_close(fd);
return 0;
}
仅限标头面向对象的版本以供重用
从文档中的示例中提取，但其形式使其易于重用。
common_v4l2.h：
#ifndef COMMON_V4L2_H
#define COMMON_V4L2_H
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/time.h>
#include <sys/types.h>
#include <libv4l2.h>
#include <linux/videodev2.h>
#define COMMON_V4L2_CLEAR(x) memset(&(x), 0, sizeof(x))
typedef struct {
void *start;
size_t length;
} CommonV4l2_Buffer;
typedef struct {
int fd;
CommonV4l2_Buffer *buffers;
struct v4l2_buffer buf;
unsigned int n_buffers;
} CommonV4l2;
void CommonV4l2_xioctl(int fh, unsigned long int request, void *arg)
{
int r;
do {
r = v4l2_ioctl(fh, request, arg);
} while (r == -1 && ((errno == EINTR) || (errno == EAGAIN)));
if (r == -1) {
fprintf(stderr, "error %d, %s\n", errno, strerror(errno));
exit(EXIT_FAILURE);
}
}
void CommonV4l2_init(CommonV4l2 *this, char *dev_name, unsigned int x_res, unsigned int y_res) {
enum v4l2_buf_type type;
struct v4l2_format fmt;
struct v4l2_requestbuffers req;
unsigned int i;
this->fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
if (this->fd < 0) {
perror("Cannot open device");
exit(EXIT_FAILURE);
}
COMMON_V4L2_CLEAR(fmt);
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = x_res;
fmt.fmt.pix.height = y_res;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_RGB24;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
CommonV4l2_xioctl(this->fd, VIDIOC_S_FMT, &fmt);
if ((fmt.fmt.pix.width != x_res) || (fmt.fmt.pix.height != y_res))
printf("Warning: driver is sending image at %dx%d\n",
fmt.fmt.pix.width, fmt.fmt.pix.height);
COMMON_V4L2_CLEAR(req);
req.count = 2;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
CommonV4l2_xioctl(this->fd, VIDIOC_REQBUFS, &req);
this->buffers = calloc(req.count, sizeof(*this->buffers));
for (this->n_buffers = 0; this->n_buffers < req.count; ++this->n_buffers) {
COMMON_V4L2_CLEAR(this->buf);
this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
this->buf.memory = V4L2_MEMORY_MMAP;
this->buf.index = this->n_buffers;
CommonV4l2_xioctl(this->fd, VIDIOC_QUERYBUF, &this->buf);
this->buffers[this->n_buffers].length = this->buf.length;
this->buffers[this->n_buffers].start = v4l2_mmap(NULL, this->buf.length,
PROT_READ | PROT_WRITE, MAP_SHARED, this->fd, this->buf.m.offset);
if (MAP_FAILED == this->buffers[this->n_buffers].start) {
perror("mmap");
exit(EXIT_FAILURE);
}
}
for (i = 0; i < this->n_buffers; ++i) {
COMMON_V4L2_CLEAR(this->buf);
this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
this->buf.memory = V4L2_MEMORY_MMAP;
this->buf.index = i;
CommonV4l2_xioctl(this->fd, VIDIOC_QBUF, &this->buf);
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
CommonV4l2_xioctl(this->fd, VIDIOC_STREAMON, &type);
}
void CommonV4l2_update_image(CommonV4l2 *this) {
fd_set fds;
int r;
struct timeval tv;
do {
FD_ZERO(&fds);
FD_SET(this->fd, &fds);
/* Timeout. */
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select(this->fd + 1, &fds, NULL, NULL, &tv);
} while ((r == -1 && (errno == EINTR)));
if (r == -1) {
perror("select");
exit(EXIT_FAILURE);
}
COMMON_V4L2_CLEAR(this->buf);
this->buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
this->buf.memory = V4L2_MEMORY_MMAP;
CommonV4l2_xioctl(this->fd, VIDIOC_DQBUF, &this->buf);
CommonV4l2_xioctl(this->fd, VIDIOC_QBUF, &this->buf);
}
char * CommonV4l2_get_image(CommonV4l2 *this) {
return ((char *)this->buffers[this->buf.index].start);
}
size_t CommonV4l2_get_image_size(CommonV4l2 *this) {
return this->buffers[this->buf.index].length;
}
void CommonV4l2_deinit(CommonV4l2 *this) {
unsigned int i;
enum v4l2_buf_type type;
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
CommonV4l2_xioctl(this->fd, VIDIOC_STREAMOFF, &type);
for (i = 0; i < this->n_buffers; ++i)
v4l2_munmap(this->buffers[i].start, this->buffers[i].length);
v4l2_close(this->fd);
free(this->buffers);
}
#endif
main.c：
#include <stdio.h>
#include <stdlib.h>
#include "common_v4l2.h"
static void save_ppm(
unsigned int i,
unsigned int x_res,
unsigned int y_res,
size_t data_lenght,
char *data
) {
FILE *fout;
char out_name[256];
sprintf(out_name, "out%03d.ppm", i);
fout = fopen(out_name, "w");
if (!fout) {
perror("error: fopen");
exit(EXIT_FAILURE);
}
fprintf(fout, "P6\n%d %d 255\n", x_res, y_res);
fwrite(data, data_lenght, 1, fout);
fclose(fout);
}
int main(void) {
CommonV4l2 common_v4l2;
char *dev_name = "/dev/video0";
struct buffer *buffers;
unsigned int
i,
x_res = 640,
y_res = 480
;
CommonV4l2_init(&common_v4l2, dev_name, x_res, y_res);
for (i = 0; i < 20; i++) {
CommonV4l2_update_image(&common_v4l2);
save_ppm(
i,
x_res,
y_res,
CommonV4l2_get_image_size(&common_v4l2),
CommonV4l2_get_image(&common_v4l2)
);
}
CommonV4l2_deinit(&common_v4l2);
return EXIT_SUCCESS;
}
<强> SDL
视频捕获在他们的路线图中：https://wiki.libsdl.org/Roadmap我打赌它将在Linux上包装v4l。
当我们获得可移植性层时，它会很好，比OpenCV更少膨胀。
答案 2 :(得分：6)
你最好的选择可能是：video4linux (V4L)
它易于使用且功能强大。