1.打开设备文件。
intfd=open(”/dev/video0″,O_RDWR);
2.取得设备的capability，看看设备具有什么功能，比如是否具有视频输入,或者音频输入输出等。VIDIOC_QUERYCAP,structv4l2_capability
v4l2_std_idstd;
do{
ret=ioctl(fd,VIDIOC_QUERYSTD,&std);
}while(ret==-1&&errno==EAGAIN);
switch(std){
caseV4L2_STD_NTSC:
//……
caseV4L2_STD_PAL:
//……
}
3.选择视频输入，一个视频设备可以有多个视频输入。VIDIOC_S_INPUT,structv4l2_input(可不要)
4.设置视频的制式和帧格式，制式包括PAL，NTSC，帧的格式个包括宽度和高度等。
VIDIOC_S_STD,VIDIOC_S_FMT,structv4l2_std_id,structv4l2_format
structv4l2_formatfmt;
memset(&fmt,0,sizeof(fmt));
fmt.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width=320;
fmt.fmt.pix.height=240;
fmt.fmt.pix.pixelformat=V4L2_PIX_FMT_JPEG;
if(ioctl(fd,VIDIOC_S_FMT,&fmt)<0）
{
printf("setformatfailed\n");
//return0;
}
5.向驱动申请帧缓冲，一般不超过5个。structv4l2_requestbuffers
structv4l2_requestbuffersreq;
memset(&req,0,sizeof(req));
req.count=4;
req.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory=V4L2_MEMORY_MMAP;
if(ioctl(fd,VIDIOC_REQBUFS,&req)==-1)
{
perror("VIDIOC_REQBUFSerror\n");
//return-1;
}
6.申请物理内存
将申请到的帧缓冲映射到用户空间，这样就可以直接操作采集到的帧了，而不必去复制。将申请到的帧缓冲全部入队列，以便存放采集到的数据.VIDIOC_QBUF,structv4l2_buffer
VideoBuffer*buffers=calloc(req.count,sizeof(VideoBuffer));
printf("sizeof(VideoBuffer)is%d\n",sizeof(VideoBuffer));
structv4l2_bufferbuf;
for(numBufs=0;numBufs
memset(&buf,0,sizeof(buf));
buf.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory=V4L2_MEMORY_MMAP;
buf.index=numBufs;
if(ioctl(fd,VIDIOC_QUERYBUF,&buf)<0)
{
printf("VIDIOC_QUERYBUFerror\n");
//return-1;
}
printf("buflenis%d\n",sizeof(buf));
//内存映射
buffers[numBufs].length=buf.length;
buffers[numBufs].offset=(size_t)buf.m.offset;
buffers[numBufs].start=mmap(NULL,buf.length,PROT_READ|PROT_WRITE,MAP_SHARED,fd,buf.m.offset);
printf("buffers.length=%d,buffers.offset=%d,buffers.start[0]=%d\n",buffers[numBufs].length,buffers[numBufs].offset,buffers[numBufs].start[0]);
printf("buf2lenis%d\n",sizeof(buffers[numBufs].start));
if(buffers[numBufs].start==MAP_FAILED)
{
perror("bufferserror\n");
//return-1;
}
if(ioctl(fd,VIDIOC_QBUF,&buf)<0)
{
printf("VIDIOC_QBUFerror\n");
//return-1;
}
}
7.开始视频的采集。
enumv4l2_buf_typetype;
type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
if(ioctl(fd,VIDIOC_STREAMON,&type)<0)
{
printf("VIDIOC_STREAMONerror\n");
//return-1;
}
8.出队列以取得已采集数据的帧缓冲，取得原始采集数据。VIDIOC_DQBUF,将缓冲重新入队列尾,这样可以循环采集。VIDIOC_QBUF
if(ioctl(fd,VIDIOC_DQBUF,&buf)<0)
{
perror("VIDIOC_DQBUFfailed.\n");
//return-1;
}
buf.type=V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory=V4L2_MEMORY_MMAP;
unsignedchar*ptcur=buffers[numBufs].start;
DEBUG("buf.bytesused=%d\n",buf.bytesused);
inti1;
for(i1=0;i1
if((buffers[numBufs].start[i1]==0x000000FF)&&(buffers[numBufs].start[i1+1]==0x000000C4))
{
DEBUG("huffmantablefinded!\nbuf.bytesused=%d\nFFC4=%d\n",buf.bytesused,i1);
break;
}
}
if(i1==buf.bytesused)printf("huffmantabledon'texist!\n");
inti;
for(i=0;i
if((buffers[numBufs].start[i]==0x000000FF)&&(buffers[numBufs].start[i+1]==0x000000D8))break;
ptcur++;
}
DEBUG("i=%d,FF=%02x,D8=%02x\n",i,buffers[numBufs].start[i],buffers[numBufs].start[i+1]);
intimagesize=buf.bytesused-i;
DEBUG("buf.bytesused=%d\n",buf.bytesused);
DEBUG("imagesize=%d\n",imagesize);
9.停止视频的采集。VIDIOC_STREAMOFF
10.关闭视频设备。close(fd);
