如何使用 c++ 使用 v4l2 API 连续捕获 h264 视频？
How to capture h264 video continuously using v4l2 API using c++?
在修改后的代码下方，(original code saves a frame into the image)，捕获一个帧并以 mp4 文件的形式保存到磁盘中。我正在尝试更改代码以从网络摄像头（Logitech c920）捕获 h264 视频帧。网络摄像头支持 h264 视频流。
如何修改代码以实时捕获和存储流式视频，直到用户退出程序？
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <linux/ioctl.h>
#include <linux/types.h>
#include <linux/v4l2-common.h>
#include <linux/v4l2-controls.h>
#include <linux/videodev2.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <string.h>
#include <fstream>
#include <string>
#include <iostream>
#include <vector>
#include <cstring>
#include <cassert>
using namespace std;
// Sepecfic to WEB Cam
short unsigned int CAM_WIDTH=1920;
short unsigned int CAM_HEIGHT=1080;
int process() {
// 1. Open the device
int fd; // A file descriptor to the video device
fd = open("/dev/video0",O_RDWR);
if(fd < 0){
perror("Failed to open device, OPEN");
return 1;
}
// 2. Ask the device if it can capture frames
v4l2_capability capability;
if(ioctl(fd, VIDIOC_QUERYCAP, &capability) < 0){
// something went wrong... exit
perror("Failed to get device capabilities, VIDIOC_QUERYCAP");
return 1;
}
// 3. Set Image format
v4l2_format imageFormat;
imageFormat.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
imageFormat.fmt.pix.width = CAM_WIDTH;
imageFormat.fmt.pix.height = CAM_HEIGHT;
imageFormat.fmt.pix.pixelformat = V4L2_PIX_FMT_H264; // V4L2_PIX_FMT_MJPEG;
imageFormat.fmt.pix.field = V4L2_FIELD_NONE;
// tell the device you are using this format
if(ioctl(fd, VIDIOC_S_FMT, &imageFormat) < 0){
perror("Device could not set format, VIDIOC_S_FMT");
return 1;
}
// 4. Request Buffers from the device
v4l2_requestbuffers requestBuffer = {0};
requestBuffer.count = 10; // one request buffer
requestBuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; // request a buffer wich we an use for capturing frames
requestBuffer.memory = V4L2_MEMORY_MMAP;
if(ioctl(fd, VIDIOC_REQBUFS, &requestBuffer) < 0){
perror("Could not request buffer from device, VIDIOC_REQBUFS");
return 1;
}
// 5. Quety the buffer to get raw data ie. ask for the you requested buffer
// and allocate memory for it
v4l2_buffer queryBuffer = {0};
queryBuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
queryBuffer.memory = V4L2_MEMORY_MMAP;
queryBuffer.index = 5;
if(ioctl(fd, VIDIOC_QUERYBUF, &queryBuffer) < 0){
perror("Device did not return the buffer information, VIDIOC_QUERYBUF");
return 1;
}
// use a pointer to point to the newly created buffer
// mmap() will map the memory address of the device to
// an address in memory
char* buffer = (char*)mmap(NULL, queryBuffer.length, PROT_READ | PROT_WRITE, MAP_SHARED,
fd, queryBuffer.m.offset);
memset(buffer, 0, queryBuffer.length);
// 6. Get a frame
// Create a new buffer type so the device knows whichbuffer we are talking about
v4l2_buffer bufferinfo;
memset(&bufferinfo, 0, sizeof(bufferinfo));
bufferinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
bufferinfo.memory = V4L2_MEMORY_MMAP;
bufferinfo.index = 0;
// Activate streaming
int type = bufferinfo.type;
if(ioctl(fd, VIDIOC_STREAMON, &type) < 0){
perror("Could not start streaming, VIDIOC_STREAMON");
return 1;
}
/***************************** Begin looping here *********************/
// Queue the buffer
if(ioctl(fd, VIDIOC_QBUF, &bufferinfo) < 0){
perror("Could not queue buffer, VIDIOC_QBUF");
return 1;
}
// Dequeue the buffer
if(ioctl(fd, VIDIOC_DQBUF, &bufferinfo) < 0){
perror("Could not dequeue the buffer, VIDIOC_DQBUF");
return 1;
}
// Frames get written after dequeuing the buffer
cout << "Buffer has: " << (double)bufferinfo.bytesused / 1024
<< " KBytes of data" << endl;
// Write the data out to file
ofstream outFile;
// outFile.open("webcam_output.jpeg", ios::binary| ios::app);
outFile.open("webcam_output.mp4", ios::binary| ios::app);
int bufPos = 0, outFileMemBlockSize = 0; // the position in the buffer and the amoun to copy from
// the buffer
int remainingBufferSize = bufferinfo.bytesused; // the remaining buffer size, is decremented by
// memBlockSize amount on each loop so we do not overwrite the buffer
uint8_t* outFileMemBlock = NULL; // a pointer to a new memory block
int itr = 0; // counts thenumber of iterations
while(remainingBufferSize > 0) {
bufPos += outFileMemBlockSize; // increment the buffer pointer on each loop
// initialise bufPos before outFileMemBlockSize so we can start
// at the begining of the buffer
outFileMemBlockSize = 1024; // set the output block size to a preferable size. 1024 :)
outFileMemBlock = new uint8_t[sizeof(uint8_t) * outFileMemBlockSize];
// copy 1024 bytes of data starting from buffer+bufPos
memcpy(outFileMemBlock, buffer+bufPos, outFileMemBlockSize);
outFile.write(outFileMemBlock,outFileMemBlockSize);
// calculate the amount of memory left to read
// if the memory block size is greater than the remaining
// amount of data we have to copy
if(outFileMemBlockSize > remainingBufferSize)
outFileMemBlockSize = remainingBufferSize;
// subtract the amount of data we have to copy
// from the remaining buffer size
remainingBufferSize -= outFileMemBlockSize;
// display the remaining buffer size
cout << itr++ << " Remaining bytes: "<< remainingBufferSize << endl;
}
// Close the file
outFile.close();
/******************************** end looping here **********************/
// end streaming
if(ioctl(fd, VIDIOC_STREAMOFF, &type) < 0){
perror("Could not end streaming, VIDIOC_STREAMOFF");
return 1;
}
close(fd);
return 0;
}
int main() {
process();
}
更新
我经历了 this example from v4l docs，但我无法 运行 这个？
#include "../libv4l/include/libv4l2.h"
由于缺少上述头文件，我无法找出如何包含这些头文件。
编写捕获网络摄像头的低级代码看起来非常复杂。但是我们可以使用 OpenCV，它更强大并且可以做与问题所问相同的事情。如果您不使用 opencv 网络摄像头功能，那么您可以看看 OpenCV 视频捕获是如何实现的。
试试这个代码 -
#include "opencv2/opencv.hpp"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat edges;
namedWindow("frame",1);
for(;;)
{
Mat frame;
cap >> frame;
imshow("frame", frame);
if(waitKey(30) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
有关如何操作的更多信息，请参见 opencv docs
在修改后的代码下方，(original code saves a frame into the image)，捕获一个帧并以 mp4 文件的形式保存到磁盘中。我正在尝试更改代码以从网络摄像头（Logitech c920）捕获 h264 视频帧。网络摄像头支持 h264 视频流。
如何修改代码以实时捕获和存储流式视频，直到用户退出程序？
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
#include <linux/ioctl.h>
#include <linux/types.h>
#include <linux/v4l2-common.h>
#include <linux/v4l2-controls.h>
#include <linux/videodev2.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <string.h>
#include <fstream>
#include <string>
#include <iostream>
#include <vector>
#include <cstring>
#include <cassert>
using namespace std;
// Sepecfic to WEB Cam
short unsigned int CAM_WIDTH=1920;
short unsigned int CAM_HEIGHT=1080;
int process() {
// 1. Open the device
int fd; // A file descriptor to the video device
fd = open("/dev/video0",O_RDWR);
if(fd < 0){
perror("Failed to open device, OPEN");
return 1;
}
// 2. Ask the device if it can capture frames
v4l2_capability capability;
if(ioctl(fd, VIDIOC_QUERYCAP, &capability) < 0){
// something went wrong... exit
perror("Failed to get device capabilities, VIDIOC_QUERYCAP");
return 1;
}
// 3. Set Image format
v4l2_format imageFormat;
imageFormat.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
imageFormat.fmt.pix.width = CAM_WIDTH;
imageFormat.fmt.pix.height = CAM_HEIGHT;
imageFormat.fmt.pix.pixelformat = V4L2_PIX_FMT_H264; // V4L2_PIX_FMT_MJPEG;
imageFormat.fmt.pix.field = V4L2_FIELD_NONE;
// tell the device you are using this format
if(ioctl(fd, VIDIOC_S_FMT, &imageFormat) < 0){
perror("Device could not set format, VIDIOC_S_FMT");
return 1;
}
// 4. Request Buffers from the device
v4l2_requestbuffers requestBuffer = {0};
requestBuffer.count = 10; // one request buffer
requestBuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; // request a buffer wich we an use for capturing frames
requestBuffer.memory = V4L2_MEMORY_MMAP;
if(ioctl(fd, VIDIOC_REQBUFS, &requestBuffer) < 0){
perror("Could not request buffer from device, VIDIOC_REQBUFS");
return 1;
}
// 5. Quety the buffer to get raw data ie. ask for the you requested buffer
// and allocate memory for it
v4l2_buffer queryBuffer = {0};
queryBuffer.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
queryBuffer.memory = V4L2_MEMORY_MMAP;
queryBuffer.index = 5;
if(ioctl(fd, VIDIOC_QUERYBUF, &queryBuffer) < 0){
perror("Device did not return the buffer information, VIDIOC_QUERYBUF");
return 1;
}
// use a pointer to point to the newly created buffer
// mmap() will map the memory address of the device to
// an address in memory
char* buffer = (char*)mmap(NULL, queryBuffer.length, PROT_READ | PROT_WRITE, MAP_SHARED,
fd, queryBuffer.m.offset);
memset(buffer, 0, queryBuffer.length);
// 6. Get a frame
// Create a new buffer type so the device knows whichbuffer we are talking about
v4l2_buffer bufferinfo;
memset(&bufferinfo, 0, sizeof(bufferinfo));
bufferinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
bufferinfo.memory = V4L2_MEMORY_MMAP;
bufferinfo.index = 0;
// Activate streaming
int type = bufferinfo.type;
if(ioctl(fd, VIDIOC_STREAMON, &type) < 0){
perror("Could not start streaming, VIDIOC_STREAMON");
return 1;
}
/***************************** Begin looping here *********************/
// Queue the buffer
if(ioctl(fd, VIDIOC_QBUF, &bufferinfo) < 0){
perror("Could not queue buffer, VIDIOC_QBUF");
return 1;
}
// Dequeue the buffer
if(ioctl(fd, VIDIOC_DQBUF, &bufferinfo) < 0){
perror("Could not dequeue the buffer, VIDIOC_DQBUF");
return 1;
}
// Frames get written after dequeuing the buffer
cout << "Buffer has: " << (double)bufferinfo.bytesused / 1024
<< " KBytes of data" << endl;
// Write the data out to file
ofstream outFile;
// outFile.open("webcam_output.jpeg", ios::binary| ios::app);
outFile.open("webcam_output.mp4", ios::binary| ios::app);
int bufPos = 0, outFileMemBlockSize = 0; // the position in the buffer and the amoun to copy from
// the buffer
int remainingBufferSize = bufferinfo.bytesused; // the remaining buffer size, is decremented by
// memBlockSize amount on each loop so we do not overwrite the buffer
uint8_t* outFileMemBlock = NULL; // a pointer to a new memory block
int itr = 0; // counts thenumber of iterations
while(remainingBufferSize > 0) {
bufPos += outFileMemBlockSize; // increment the buffer pointer on each loop
// initialise bufPos before outFileMemBlockSize so we can start
// at the begining of the buffer
outFileMemBlockSize = 1024; // set the output block size to a preferable size. 1024 :)
outFileMemBlock = new uint8_t[sizeof(uint8_t) * outFileMemBlockSize];
// copy 1024 bytes of data starting from buffer+bufPos
memcpy(outFileMemBlock, buffer+bufPos, outFileMemBlockSize);
outFile.write(outFileMemBlock,outFileMemBlockSize);
// calculate the amount of memory left to read
// if the memory block size is greater than the remaining
// amount of data we have to copy
if(outFileMemBlockSize > remainingBufferSize)
outFileMemBlockSize = remainingBufferSize;
// subtract the amount of data we have to copy
// from the remaining buffer size
remainingBufferSize -= outFileMemBlockSize;
// display the remaining buffer size
cout << itr++ << " Remaining bytes: "<< remainingBufferSize << endl;
}
// Close the file
outFile.close();
/******************************** end looping here **********************/
// end streaming
if(ioctl(fd, VIDIOC_STREAMOFF, &type) < 0){
perror("Could not end streaming, VIDIOC_STREAMOFF");
return 1;
}
close(fd);
return 0;
}
int main() {
process();
}
更新 我经历了 this example from v4l docs，但我无法 运行 这个？
#include "../libv4l/include/libv4l2.h"
由于缺少上述头文件，我无法找出如何包含这些头文件。
编写捕获网络摄像头的低级代码看起来非常复杂。但是我们可以使用 OpenCV，它更强大并且可以做与问题所问相同的事情。如果您不使用 opencv 网络摄像头功能，那么您可以看看 OpenCV 视频捕获是如何实现的。
试试这个代码 -
#include "opencv2/opencv.hpp"
using namespace cv;
int main(int, char**)
{
VideoCapture cap(0); // open the default camera
if(!cap.isOpened()) // check if we succeeded
return -1;
Mat edges;
namedWindow("frame",1);
for(;;)
{
Mat frame;
cap >> frame;
imshow("frame", frame);
if(waitKey(30) >= 0) break;
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
有关如何操作的更多信息，请参见 opencv docs