我想从V4L2设备(从树莓派相机)录制一个C的视频。录制本身工作,我可以将视频保存到一个文件。
但是,我需要更改视频的比特率。从v4l2-ctl --set-ctrl video_bitrate=10000000命令的strace输出中,我知道可以使用v4l2的扩展控件API来实现这一点。
下面是我的代码,到目前为止还不起作用:
#include <iostream>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <sys/mman.h> //mmap
#include <fcntl.h>
#include <unistd.h>
#include <linux/videodev2.h>
using namespace std;
#define numbuffers 3
struct picturebuffer
{
void *startadress;
size_t length;
};
//array in which the buffer pointer are being stored
picturebuffer pb[numbuffers];
int main()
{
//open camera
int fd;
fd = open("/dev/video0", O_RDWR);
if(fd < 0)
{
cout << "error during opening the camera device!";
cout.flush();
}
cout << "camera opened";
//read capabilities
struct v4l2_capability caps;
if(ioctl(fd, VIDIOC_QUERYCAP, &caps) < 0)
{
cout << "error while reading the capabilities!";
cout.flush();
}
cout << "Capabilities " << caps.capabilities << endl;
//ToDo: check for required capabilities
//set image data
struct v4l2_format format;
format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
format.fmt.pix.pixelformat = V4L2_PIX_FMT_H264;
format.fmt.pix.width = 1920;
format.fmt.pix.height = 1080;
if(ioctl(fd, VIDIOC_S_FMT, &format) < 0)
{
cout << "error in the image format";
}
cout << "Image properties set" << endl;
//Todo: check if width and height fit together (VIDIOC_ENUM_FRAMESIZES)
//set extended Controls
struct v4l2_ext_controls ecs;
struct v4l2_ext_control ec;
memset(&ecs, 0, sizeof(ecs));
memset(&ec, 0, sizeof(ec));
ec.id = V4L2_CID_MPEG_VIDEO_BITRATE;
ec.value = 10000000;
ec.size = 0;
ecs.controls = &ec;
ecs.count = 1;
ecs.ctrl_class = V4L2_CTRL_CLASS_MPEG;
if(ioctl(fd, VIDIOC_S_EXT_CTRLS, &ecs) < 0)
{
cout << "error in extended controls bitrate";
cout.flush();
}
//allocate buffer in the kernel
struct v4l2_requestbuffers req;
req.count = numbuffers;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if(ioctl(fd, VIDIOC_REQBUFS, &req) < 0)
{
cout << "errro while allocating buffer";
cout.flush();
}
cout << "number of buffers: " << req.count << endl;
cout.flush();
//map buffers into userspace
for(int i=0; i<numbuffers; i++)
{
struct v4l2_buffer bufferinfo;
memset(&bufferinfo, 0, sizeof(bufferinfo));
bufferinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
bufferinfo.memory = V4L2_MEMORY_MMAP;
bufferinfo.index = i;
if(ioctl(fd, VIDIOC_QUERYBUF, &bufferinfo) < 0)
{
cout << "error while querying bufferinfo";
cout.flush();
}
pb[i].startadress = mmap(NULL, bufferinfo.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, bufferinfo.m.offset);
pb[i].length = bufferinfo.length;
if(pb[i].startadress == MAP_FAILED)
{
cout << "error during mmap" << endl;
}
memset(pb[i].startadress, 0, bufferinfo.length);
cout << "size of buffer: " << bufferinfo.length << endl;
}
cout << "buffers mapped into userspace" << endl;
cout.flush();
//queue in the buffers
for(int i=0; i<numbuffers; i++)
{
struct v4l2_buffer bufferinfo;
memset(&bufferinfo, 0, sizeof(bufferinfo));
bufferinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
bufferinfo.memory = V4L2_MEMORY_MMAP;
bufferinfo.index = i;
if(ioctl(fd, VIDIOC_QBUF, &bufferinfo) < 0)
{
cout << "error while queueing the buffers in" << endl;
}
}
//since that point the driver starts capturing the pics
int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if(ioctl(fd, VIDIOC_STREAMON, &type) < 0)
{
cout << "error while starting the stream" << endl;
}
int file;
if((file = open("/home/pi/image.h264", O_WRONLY | O_CREAT, 0660)) < 0)
{
cout << "error while writing the file";
}
//loop for managing the pics
for(int i=0; i<100; i++)
{
struct v4l2_buffer bufferinfo;
memset(&bufferinfo, 0, sizeof(bufferinfo));
bufferinfo.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
bufferinfo.memory = V4L2_MEMORY_MMAP;
if(ioctl(fd, VIDIOC_DQBUF, &bufferinfo) < 0)
{
cout << "error while getting the buffer!" << endl;
}
//do anything with the pic
char buf[pb[bufferinfo.index].length];
memcpy(&buf, pb[bufferinfo.index].startadress, pb[bufferinfo.index].length);
cout << bufferinfo.index << endl;
cout.flush();
//write picture into the file
write(file, pb[bufferinfo.index].startadress, pb[bufferinfo.index].length);
if(ioctl(fd, VIDIOC_QBUF, &bufferinfo) < 0)
{
cout << "error while enqueuing the buffer" << endl;
}
}
close(file);
if(ioctl(fd, VIDIOC_STREAMOFF, &type) < 0)
{
cout << "error while stopping the stream" << endl;
}
//clean up
for(int i=0; i<numbuffers; i++)
{
if(munmap(pb[i].startadress, pb[i].length) < 0)
{
cout << "error during unmap";
}
}
//close camera file
close(fd);
cout << "!World!" << endl;
cout.flush();
return 0;
}
ioctl调用似乎成功了,但是我的输出文件的大小始终与199,2MB相同。有人知道代码出了什么问题吗?
发布于 2017-03-03 13:16:23
您需要检查摄像头驱动程序是否支持该IOCTL命令。如果驱动程序由于不实现而不支持IOCTL命令,您仍然可以执行该命令,并且该命令将被路由到v4l2默认实现,摄像机设置不会应用任何实际更改
https://stackoverflow.com/questions/38007305
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