video4linux

这次是在linux下开发摄像头的程序,主要用的是video4linux来做的,界面用qt来实现,开始准备用frame buffer来直接写屏但是效果不怎么好,后来就用qt来做了,这样用起来效果还蛮好的,帧率也可以,可以上到30fps;运用v4l来编程主要掌握其 api,要提高帧率最重要的是用到内存映射,其实用qt和frame buffer的时候都要用到内存映射来做,只有这样才可以达到较高的帧率,不过要注意资源的利用问题.mmap后一定要munmap.对于frame buffer是很有意思的一个东西,特别是驱动的设计.
代码如下:
1.open device:
      video_dev = open("\dev\video0",O_RDWR));
2.get the information of the video device
    struct video_capability video_cap;
    memset(&video_cap,0,sizeof(video_cap));
    if(ioctl(video_dev,VIDIOCGCAP,&video_cap) == -1)
    {
        perror("Cann't get the information of the video device");
        close(video_dev);
        exit(1);
    }
3.get the information of the channels
    struct video_channel video_chan;
    memset(&video_chan,0,sizeof(video_chan));
    for(channel = 0;channel < video_cap.channels;channel++)
    {
        video_chan.channel = channel;
        if(ioctl(video_dev,VIDIOCGCHAN,&video_chan) == -1)
        {
            perror("Cann't get the information of the channels");
            close(video_dev);
            exit(3);
        }
        if(video_chan.type == VIDEO_TYPE_TV)
        {
                  #ifdef DEBUG
            printf("NO.%d channel is %s,type is tv!\n",channel,video_chan.name);
                  #endif
        }
        if(video_chan.type == VIDEO_TYPE_CAMERA)
        {
            if(ioctl(video_dev,VIDIOCSCHAN,&video_chan) == -1)
            {
                perror("Cann't set the camera channel!");
                close(video_dev);
                exit(4);
            }
        }
    }
4.get the capture attributes
    struct video_picture video_pic;
    memset(&video_pic,0,sizeof(video_pic));
    if(ioctl(video_dev,VIDIOCGPICT,&video_pic) == -1)
    {
        perror("Cann't get the picture attributes of the device!");
        close(video_dev);
        exit(5);
    }
5.set capture attributes
      video_pic.palette = VIDEO_PALETTE_*****;//different camera has different palette
      video_pic.brightness = 65535;
    video_pic.colour = 0;
    if(ioctl(video_dev,VIDIOCSPICT,&video_pic) == -1)
    {
        perror("Cann't set the picture attributs!");
        close(video_dev);
        exit(6);
    }
6.mmap the device
    struct video_mbuf mbuf;
    unsigned char *frames;
    memset(&mbuf,0,sizeof(mbuf));
    if(ioctl(video_dev,VIDIOCGMBUF,&mbuf) == -1)   
    {
        perror("Cann't get the buffer information of the video device!");
        close(video_dev);
        exit(7);
    }
    frames = (unsigned char *)::mmap(0,mbuf.size,PROT_READ|PROT_WRITE,MAP_SHARED,video_dev,0);
    if(!frames || frames == (unsigned char *)(long)(-1))
    {
        perror("The device cann't be memory mapped!");
        close(video_dev);
        exit(8);
    }
7.capture
            if(ioctl(video_dev,VIDIOCMCAPTURE,&mmap) == -1)
        {
            perror("Capture failed!");
            close(video_dev);
            exit(9);
        }
   
        else
        {
                  //display or save the picture file
            }