第一次使用v4l2

主要參考鏈接:http://jwhsmith.net/2014/12/capturing-a-webcam-stream-using-v4l2/
這篇文章把v4l2編程的九個步驟說的很詳細 最後用SDL 把圖像顯示出來
其實你需要的都在這:http://linuxtv.org/downloads/v4l-dvb-apis/
然而卻沒心看~~~~~
那只好github了
1https://github.com/twam/v4l2grab 這個是最完整的攝像頭拍照源碼 支持read mmap userptr三種方式
需要libv4l2庫 libjpeg庫 交叉編譯的時候還需要-lrt -lm -lpthread
libv4l2:https://github.com/philips/libv4l
這個是之前版本v0.1 單文件的http://www.twam.info/software/v4l2grab-grabbing-jpegs-from-v4l2-devices
我的攝像頭是logitech C270 HD720P的 用v0.1只能抓176*144的圖片 用v0.3的話能抓1280*960 具體為什麼沒對比
2https://github.com/joeshang/joycar/tree/master/module/v4l2_camera 這個帥小伙做的智能車 上面有視頻采集模塊
采集出來的圖片是以 ffd8開頭 ffd9結尾的 但是卻用圖片工具卻打不開 linux下的看圖提示huffman table 未定義
加入了huffman table後 圖片可以打開了
下面是代碼

const static unsigned char dht_data[] = {
    0xff, 0xc4, 0x01, 0xa2, 0x00, 0x00, 0x01, 0x05, 0x01, 0x01, 0x01, 0x01,
    0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x02,
    0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x01, 0x00, 0x03,
    0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09,
    0x0a, 0x0b, 0x10, 0x00, 0x02, 0x01, 0x03, 0x03, 0x02, 0x04, 0x03, 0x05,
    0x05, 0x04, 0x04, 0x00, 0x00, 0x01, 0x7d, 0x01, 0x02, 0x03, 0x00, 0x04,
    0x11, 0x05, 0x12, 0x21, 0x31, 0x41, 0x06, 0x13, 0x51, 0x61, 0x07, 0x22,
    0x71, 0x14, 0x32, 0x81, 0x91, 0xa1, 0x08, 0x23, 0x42, 0xb1, 0xc1, 0x15,
    0x52, 0xd1, 0xf0, 0x24, 0x33, 0x62, 0x72, 0x82, 0x09, 0x0a, 0x16, 0x17,
    0x18, 0x19, 0x1a, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x34, 0x35, 0x36,
    0x37, 0x38, 0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a,
    0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x63, 0x64, 0x65, 0x66,
    0x67, 0x68, 0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a,
    0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x92, 0x93, 0x94, 0x95,
    0x96, 0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, 0xa8,
    0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba, 0xc2,
    0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4, 0xd5,
    0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe1, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
    0xe8, 0xe9, 0xea, 0xf1, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9,
    0xfa, 0x11, 0x00, 0x02, 0x01, 0x02, 0x04, 0x04, 0x03, 0x04, 0x07, 0x05,
    0x04, 0x04, 0x00, 0x01, 0x02, 0x77, 0x00, 0x01, 0x02, 0x03, 0x11, 0x04,
    0x05, 0x21, 0x31, 0x06, 0x12, 0x41, 0x51, 0x07, 0x61, 0x71, 0x13, 0x22,
    0x32, 0x81, 0x08, 0x14, 0x42, 0x91, 0xa1, 0xb1, 0xc1, 0x09, 0x23, 0x33,
    0x52, 0xf0, 0x15, 0x62, 0x72, 0xd1, 0x0a, 0x16, 0x24, 0x34, 0xe1, 0x25,
    0xf1, 0x17, 0x18, 0x19, 0x1a, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x35, 0x36,
    0x37, 0x38, 0x39, 0x3a, 0x43, 0x44, 0x45, 0x46, 0x47, 0x48, 0x49, 0x4a,
    0x53, 0x54, 0x55, 0x56, 0x57, 0x58, 0x59, 0x5a, 0x63, 0x64, 0x65, 0x66,
    0x67, 0x68, 0x69, 0x6a, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7a,
    0x82, 0x83, 0x84, 0x85, 0x86, 0x87, 0x88, 0x89, 0x8a, 0x92, 0x93, 0x94,
    0x95, 0x96, 0x97, 0x98, 0x99, 0x9a, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7,
    0xa8, 0xa9, 0xaa, 0xb2, 0xb3, 0xb4, 0xb5, 0xb6, 0xb7, 0xb8, 0xb9, 0xba,
    0xc2, 0xc3, 0xc4, 0xc5, 0xc6, 0xc7, 0xc8, 0xc9, 0xca, 0xd2, 0xd3, 0xd4,
    0xd5, 0xd6, 0xd7, 0xd8, 0xd9, 0xda, 0xe2, 0xe3, 0xe4, 0xe5, 0xe6, 0xe7,
    0xe8, 0xe9, 0xea, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6, 0xf7, 0xf8, 0xf9, 0xfa
};

int is_huffman(unsigned char *buf)
{
    unsigned char *ptbuf;
    int i = 0;
    ptbuf = buf;
    while(((ptbuf[0] << 8) | ptbuf[1]) != 0xffda) {
        if(i++ > 2048)
            return 0;
        if(((ptbuf[0] << 8) | ptbuf[1]) == 0xffc4)
            return 1;
        ptbuf++;
    }
    return 0;
}
int memcpy_picture(unsigned char *out, unsigned char *buf, int size)
{
    unsigned char *ptdeb, *ptlimit, *ptcur = buf;
    int sizein, pos = 0;

    if(!is_huffman(buf)) {
        ptdeb = ptcur = buf;
        ptlimit = buf + size;
        while((((ptcur[0] << 8) | ptcur[1]) != 0xffc0) && (ptcur < ptlimit))
            ptcur++;
        if(ptcur >= ptlimit)
            return pos;
        sizein = ptcur - ptdeb;

        memcpy(out + pos, buf, sizein); pos += sizein;
        memcpy(out + pos, dht_data, sizeof(dht_data)); pos += sizeof(dht_data);
        memcpy(out + pos, ptcur, size - sizein); pos += size - sizein;
    } else {
        memcpy(out + pos, ptcur, size); pos += size;
    }
    return pos;
}

代碼是在別處復制粘貼的
看過mjpeg-streamer源碼的同志會不會很眼熟
還有一點問題 1280*920的圖片 只能拍一半,,,,,呵呵 不管了 用不到那麼大的
不過希望有人能告訴我