linux arm64 opencv 使用MJPG获取摄像头图片

先上代码

#include <opencv2/opencv.hpp>cv::VideoCapture capture(9, cv::CAP_V4L2);if (!capture.isOpened()){qDebug() << "打开摄像头失败";return  -1;}if(1){// 设置为 'MJPG' (Motion-JPEG, compressed)qDebug() << "MJPEG:" << cv::VideoWriter::fourcc('M','J','P','G');qDebug() << "get CAP_PROP_FOURCC:" << (int)capture.get(cv::CAP_PROP_FOURCC);qDebug() << "set CAP_PROP_FOURCC:" << capture.set(cv::CAP_PROP_FOURCC, cv::VideoWriter::fourcc('M','J','P','G'));qDebug() << "get CAP_PROP_FOURCC:" << (int)capture.get(cv::CAP_PROP_FOURCC);}if(0){// 设置为 'YUYV' (YUYV 4:2:2)qDebug() << "YUYV:" << cv::VideoWriter::fourcc('Y', 'U', 'Y', '2');qDebug() << "get CAP_PROP_FOURCC:" << (int)capture.get(cv::CAP_PROP_FOURCC);qDebug() << "set CAP_PROP_FOURCC:" << capture.set(cv::CAP_PROP_FOURCC, cv::VideoWriter::fourcc('Y', 'U', 'Y', '2'));qDebug() << "get CAP_PROP_FOURCC:" << (int)capture.get(cv::CAP_PROP_FOURCC);}// Set frame widthcapture.set(cv::CAP_PROP_FRAME_WIDTH, 1920);// Set frame heightcapture.set(cv::CAP_PROP_FRAME_HEIGHT, 1080);// Set FPSqDebug() << "set CAP_PROP_FPS:" << capture.set(cv::CAP_PROP_FPS, 25);cv::Mat imgFrame;capture >> imgFrame;//capture.read(imgFrame);//capture.grab(); capture.retrieve(imgFrame, 0); // retrieve需要调用grabqDebug() << "image save:" << cv::imwrite("/root/uvc.jpg", imgFrame);cv::imshow("img", imgFrame);//cv::waitKey(0);capture.release();

cv::VideoCapture capture(9, cv::CAP_V4L2)第二个参数apiPreference比较重要，默认值为cv::CAP_ANY，部分板子使用默认值是无法配置MJPG的，只能使用YUYV格式，默认值估计是cv::CAP_GSTREAMER

cv::CAP_GSTREAMER 调用capture.set都会返回false, 不能使用'MJPG' (Motion-JPEG, compressed)，只支持'YUYV' (YUYV 4:2:2), 帧率设置不对就会无法读取图像
cv::CAP_V4L2 调用capture.set都会返回true，帧率设置错误也能读取图像

cv::VideoWriter::fourcc('M','J','P','G')中参数值可以参考（CAP_PROP_CODEC_PIXEL_FORMAT后面注释写的）：https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/raw.c

这里列一下：

static const PixelFormatTag raw_pix_fmt_tags[] = {{ AV_PIX_FMT_YUV420P, MKTAG('I', '4', '2', '0') }, /* Planar formats */{ AV_PIX_FMT_YUV420P, MKTAG('I', 'Y', 'U', 'V') },{ AV_PIX_FMT_YUV420P, MKTAG('y', 'v', '1', '2') },{ AV_PIX_FMT_YUV420P, MKTAG('Y', 'V', '1', '2') },{ AV_PIX_FMT_YUV410P, MKTAG('Y', 'U', 'V', '9') },{ AV_PIX_FMT_YUV410P, MKTAG('Y', 'V', 'U', '9') },{ AV_PIX_FMT_YUV411P, MKTAG('Y', '4', '1', 'B') },{ AV_PIX_FMT_YUV422P, MKTAG('Y', '4', '2', 'B') },{ AV_PIX_FMT_YUV422P, MKTAG('P', '4', '2', '2') },{ AV_PIX_FMT_YUV422P, MKTAG('Y', 'V', '1', '6') },/* yuvjXXX formats are deprecated hacks specific to libav*,they are identical to yuvXXX  */{ AV_PIX_FMT_YUVJ420P, MKTAG('I', '4', '2', '0') }, /* Planar formats */{ AV_PIX_FMT_YUVJ420P, MKTAG('I', 'Y', 'U', 'V') },{ AV_PIX_FMT_YUVJ420P, MKTAG('Y', 'V', '1', '2') },{ AV_PIX_FMT_YUVJ422P, MKTAG('Y', '4', '2', 'B') },{ AV_PIX_FMT_YUVJ422P, MKTAG('P', '4', '2', '2') },{ AV_PIX_FMT_GRAY8,    MKTAG('Y', '8', '0', '0') },{ AV_PIX_FMT_GRAY8,    MKTAG('Y', '8', ' ', ' ') },{ AV_PIX_FMT_YUYV422, MKTAG('Y', 'U', 'Y', '2') }, /* Packed formats */{ AV_PIX_FMT_YUYV422, MKTAG('Y', '4', '2', '2') },{ AV_PIX_FMT_YUYV422, MKTAG('V', '4', '2', '2') },{ AV_PIX_FMT_YUYV422, MKTAG('V', 'Y', 'U', 'Y') },{ AV_PIX_FMT_YUYV422, MKTAG('Y', 'U', 'N', 'V') },{ AV_PIX_FMT_YUYV422, MKTAG('Y', 'U', 'Y', 'V') },{ AV_PIX_FMT_YVYU422, MKTAG('Y', 'V', 'Y', 'U') }, /* Philips */{ AV_PIX_FMT_UYVY422, MKTAG('U', 'Y', 'V', 'Y') },{ AV_PIX_FMT_UYVY422, MKTAG('H', 'D', 'Y', 'C') },{ AV_PIX_FMT_UYVY422, MKTAG('U', 'Y', 'N', 'V') },{ AV_PIX_FMT_UYVY422, MKTAG('U', 'Y', 'N', 'Y') },{ AV_PIX_FMT_UYVY422, MKTAG('u', 'y', 'v', '1') },{ AV_PIX_FMT_UYVY422, MKTAG('2', 'V', 'u', '1') },{ AV_PIX_FMT_UYVY422, MKTAG('A', 'V', 'R', 'n') }, /* Avid AVI Codec 1:1 */{ AV_PIX_FMT_UYVY422, MKTAG('A', 'V', '1', 'x') }, /* Avid 1:1x */{ AV_PIX_FMT_UYVY422, MKTAG('A', 'V', 'u', 'p') },{ AV_PIX_FMT_UYVY422, MKTAG('V', 'D', 'T', 'Z') }, /* SoftLab-NSK VideoTizer */{ AV_PIX_FMT_UYVY422, MKTAG('a', 'u', 'v', '2') },{ AV_PIX_FMT_UYVY422, MKTAG('c', 'y', 'u', 'v') }, /* CYUV is also Creative YUV */{ AV_PIX_FMT_UYYVYY411, MKTAG('Y', '4', '1', '1') },{ AV_PIX_FMT_GRAY8,   MKTAG('G', 'R', 'E', 'Y') },{ AV_PIX_FMT_NV12,    MKTAG('N', 'V', '1', '2') },{ AV_PIX_FMT_NV21,    MKTAG('N', 'V', '2', '1') },{ AV_PIX_FMT_VUYA,    MKTAG('A', 'Y', 'U', 'V') }, /* MS 4:4:4:4 *//* nut */{ AV_PIX_FMT_RGB555LE, MKTAG('R', 'G', 'B', 15) },{ AV_PIX_FMT_BGR555LE, MKTAG('B', 'G', 'R', 15) },{ AV_PIX_FMT_RGB565LE, MKTAG('R', 'G', 'B', 16) },{ AV_PIX_FMT_BGR565LE, MKTAG('B', 'G', 'R', 16) },{ AV_PIX_FMT_RGB555BE, MKTAG(15 , 'B', 'G', 'R') },{ AV_PIX_FMT_BGR555BE, MKTAG(15 , 'R', 'G', 'B') },{ AV_PIX_FMT_RGB565BE, MKTAG(16 , 'B', 'G', 'R') },{ AV_PIX_FMT_BGR565BE, MKTAG(16 , 'R', 'G', 'B') },{ AV_PIX_FMT_RGB444LE, MKTAG('R', 'G', 'B', 12) },{ AV_PIX_FMT_BGR444LE, MKTAG('B', 'G', 'R', 12) },{ AV_PIX_FMT_RGB444BE, MKTAG(12 , 'B', 'G', 'R') },{ AV_PIX_FMT_BGR444BE, MKTAG(12 , 'R', 'G', 'B') },{ AV_PIX_FMT_RGBA64LE, MKTAG('R', 'B', 'A', 64 ) },{ AV_PIX_FMT_BGRA64LE, MKTAG('B', 'R', 'A', 64 ) },{ AV_PIX_FMT_RGBA64BE, MKTAG(64 , 'R', 'B', 'A') },{ AV_PIX_FMT_BGRA64BE, MKTAG(64 , 'B', 'R', 'A') },{ AV_PIX_FMT_RGBA,     MKTAG('R', 'G', 'B', 'A') },{ AV_PIX_FMT_RGB0,     MKTAG('R', 'G', 'B',  0 ) },{ AV_PIX_FMT_BGRA,     MKTAG('B', 'G', 'R', 'A') },{ AV_PIX_FMT_BGR0,     MKTAG('B', 'G', 'R',  0 ) },{ AV_PIX_FMT_ABGR,     MKTAG('A', 'B', 'G', 'R') },{ AV_PIX_FMT_0BGR,     MKTAG( 0 , 'B', 'G', 'R') },{ AV_PIX_FMT_ARGB,     MKTAG('A', 'R', 'G', 'B') },{ AV_PIX_FMT_0RGB,     MKTAG( 0 , 'R', 'G', 'B') },{ AV_PIX_FMT_RGB24,    MKTAG('R', 'G', 'B', 24 ) },{ AV_PIX_FMT_BGR24,    MKTAG('B', 'G', 'R', 24 ) },{ AV_PIX_FMT_YUV411P,  MKTAG('4', '1', '1', 'P') },{ AV_PIX_FMT_YUV422P,  MKTAG('4', '2', '2', 'P') },{ AV_PIX_FMT_YUVJ422P, MKTAG('4', '2', '2', 'P') },{ AV_PIX_FMT_YUV440P,  MKTAG('4', '4', '0', 'P') },{ AV_PIX_FMT_YUVJ440P, MKTAG('4', '4', '0', 'P') },{ AV_PIX_FMT_YUV444P,  MKTAG('4', '4', '4', 'P') },{ AV_PIX_FMT_YUVJ444P, MKTAG('4', '4', '4', 'P') },{ AV_PIX_FMT_MONOWHITE,MKTAG('B', '1', 'W', '0') },{ AV_PIX_FMT_MONOBLACK,MKTAG('B', '0', 'W', '1') },{ AV_PIX_FMT_BGR8,     MKTAG('B', 'G', 'R',  8 ) },{ AV_PIX_FMT_RGB8,     MKTAG('R', 'G', 'B',  8 ) },{ AV_PIX_FMT_BGR4,     MKTAG('B', 'G', 'R',  4 ) },{ AV_PIX_FMT_RGB4,     MKTAG('R', 'G', 'B',  4 ) },{ AV_PIX_FMT_RGB4_BYTE,MKTAG('B', '4', 'B', 'Y') },{ AV_PIX_FMT_BGR4_BYTE,MKTAG('R', '4', 'B', 'Y') },{ AV_PIX_FMT_RGB48LE,  MKTAG('R', 'G', 'B', 48 ) },{ AV_PIX_FMT_RGB48BE,  MKTAG( 48, 'R', 'G', 'B') },{ AV_PIX_FMT_BGR48LE,  MKTAG('B', 'G', 'R', 48 ) },{ AV_PIX_FMT_BGR48BE,  MKTAG( 48, 'B', 'G', 'R') },{ AV_PIX_FMT_GRAY9LE,     MKTAG('Y', '1',  0 ,  9 ) },{ AV_PIX_FMT_GRAY9BE,     MKTAG( 9 ,  0 , '1', 'Y') },{ AV_PIX_FMT_GRAY10LE,    MKTAG('Y', '1',  0 , 10 ) },{ AV_PIX_FMT_GRAY10BE,    MKTAG(10 ,  0 , '1', 'Y') },{ AV_PIX_FMT_GRAY12LE,    MKTAG('Y', '1',  0 , 12 ) },{ AV_PIX_FMT_GRAY12BE,    MKTAG(12 ,  0 , '1', 'Y') },{ AV_PIX_FMT_GRAY14LE,    MKTAG('Y', '1',  0 , 14 ) },{ AV_PIX_FMT_GRAY14BE,    MKTAG(14 ,  0 , '1', 'Y') },{ AV_PIX_FMT_GRAY16LE,    MKTAG('Y', '1',  0 , 16 ) },{ AV_PIX_FMT_GRAY16BE,    MKTAG(16 ,  0 , '1', 'Y') },{ AV_PIX_FMT_YUV420P9LE,  MKTAG('Y', '3', 11 ,  9 ) },{ AV_PIX_FMT_YUV420P9BE,  MKTAG( 9 , 11 , '3', 'Y') },{ AV_PIX_FMT_YUV422P9LE,  MKTAG('Y', '3', 10 ,  9 ) },{ AV_PIX_FMT_YUV422P9BE,  MKTAG( 9 , 10 , '3', 'Y') },{ AV_PIX_FMT_YUV444P9LE,  MKTAG('Y', '3',  0 ,  9 ) },{ AV_PIX_FMT_YUV444P9BE,  MKTAG( 9 ,  0 , '3', 'Y') },{ AV_PIX_FMT_YUV420P10LE, MKTAG('Y', '3', 11 , 10 ) },{ AV_PIX_FMT_YUV420P10BE, MKTAG(10 , 11 , '3', 'Y') },{ AV_PIX_FMT_YUV422P10LE, MKTAG('Y', '3', 10 , 10 ) },{ AV_PIX_FMT_YUV422P10BE, MKTAG(10 , 10 , '3', 'Y') },{ AV_PIX_FMT_YUV444P10LE, MKTAG('Y', '3',  0 , 10 ) },{ AV_PIX_FMT_YUV444P10BE, MKTAG(10 ,  0 , '3', 'Y') },{ AV_PIX_FMT_YUV420P12LE, MKTAG('Y', '3', 11 , 12 ) },{ AV_PIX_FMT_YUV420P12BE, MKTAG(12 , 11 , '3', 'Y') },{ AV_PIX_FMT_YUV422P12LE, MKTAG('Y', '3', 10 , 12 ) },{ AV_PIX_FMT_YUV422P12BE, MKTAG(12 , 10 , '3', 'Y') },{ AV_PIX_FMT_YUV444P12LE, MKTAG('Y', '3',  0 , 12 ) },{ AV_PIX_FMT_YUV444P12BE, MKTAG(12 ,  0 , '3', 'Y') },{ AV_PIX_FMT_YUV420P14LE, MKTAG('Y', '3', 11 , 14 ) },{ AV_PIX_FMT_YUV420P14BE, MKTAG(14 , 11 , '3', 'Y') },{ AV_PIX_FMT_YUV422P14LE, MKTAG('Y', '3', 10 , 14 ) },{ AV_PIX_FMT_YUV422P14BE, MKTAG(14 , 10 , '3', 'Y') },{ AV_PIX_FMT_YUV444P14LE, MKTAG('Y', '3',  0 , 14 ) },{ AV_PIX_FMT_YUV444P14BE, MKTAG(14 ,  0 , '3', 'Y') },{ AV_PIX_FMT_YUV420P16LE, MKTAG('Y', '3', 11 , 16 ) },{ AV_PIX_FMT_YUV420P16BE, MKTAG(16 , 11 , '3', 'Y') },{ AV_PIX_FMT_YUV422P16LE, MKTAG('Y', '3', 10 , 16 ) },{ AV_PIX_FMT_YUV422P16BE, MKTAG(16 , 10 , '3', 'Y') },{ AV_PIX_FMT_YUV444P16LE, MKTAG('Y', '3',  0 , 16 ) },{ AV_PIX_FMT_YUV444P16BE, MKTAG(16 ,  0 , '3', 'Y') },{ AV_PIX_FMT_YUVA420P,    MKTAG('Y', '4', 11 ,  8 ) },{ AV_PIX_FMT_YUVA422P,    MKTAG('Y', '4', 10 ,  8 ) },{ AV_PIX_FMT_YUVA444P,    MKTAG('Y', '4',  0 ,  8 ) },{ AV_PIX_FMT_YA8,         MKTAG('Y', '2',  0 ,  8 ) },{ AV_PIX_FMT_PAL8,        MKTAG('P', 'A', 'L',  8 ) },{ AV_PIX_FMT_YUVA420P9LE,  MKTAG('Y', '4', 11 ,  9 ) },{ AV_PIX_FMT_YUVA420P9BE,  MKTAG( 9 , 11 , '4', 'Y') },{ AV_PIX_FMT_YUVA422P9LE,  MKTAG('Y', '4', 10 ,  9 ) },{ AV_PIX_FMT_YUVA422P9BE,  MKTAG( 9 , 10 , '4', 'Y') },{ AV_PIX_FMT_YUVA444P9LE,  MKTAG('Y', '4',  0 ,  9 ) },{ AV_PIX_FMT_YUVA444P9BE,  MKTAG( 9 ,  0 , '4', 'Y') },{ AV_PIX_FMT_YUVA420P10LE, MKTAG('Y', '4', 11 , 10 ) },{ AV_PIX_FMT_YUVA420P10BE, MKTAG(10 , 11 , '4', 'Y') },{ AV_PIX_FMT_YUVA422P10LE, MKTAG('Y', '4', 10 , 10 ) },{ AV_PIX_FMT_YUVA422P10BE, MKTAG(10 , 10 , '4', 'Y') },{ AV_PIX_FMT_YUVA444P10LE, MKTAG('Y', '4',  0 , 10 ) },{ AV_PIX_FMT_YUVA444P10BE, MKTAG(10 ,  0 , '4', 'Y') },{ AV_PIX_FMT_YUVA422P12LE, MKTAG('Y', '4', 10 , 12 ) },{ AV_PIX_FMT_YUVA422P12BE, MKTAG(12 , 10 , '4', 'Y') },{ AV_PIX_FMT_YUVA444P12LE, MKTAG('Y', '4',  0 , 12 ) },{ AV_PIX_FMT_YUVA444P12BE, MKTAG(12 ,  0 , '4', 'Y') },{ AV_PIX_FMT_YUVA420P16LE, MKTAG('Y', '4', 11 , 16 ) },{ AV_PIX_FMT_YUVA420P16BE, MKTAG(16 , 11 , '4', 'Y') },{ AV_PIX_FMT_YUVA422P16LE, MKTAG('Y', '4', 10 , 16 ) },{ AV_PIX_FMT_YUVA422P16BE, MKTAG(16 , 10 , '4', 'Y') },{ AV_PIX_FMT_YUVA444P16LE, MKTAG('Y', '4',  0 , 16 ) },{ AV_PIX_FMT_YUVA444P16BE, MKTAG(16 ,  0 , '4', 'Y') },{ AV_PIX_FMT_GBRP,         MKTAG('G', '3', 00 ,  8 ) },{ AV_PIX_FMT_GBRP9LE,      MKTAG('G', '3', 00 ,  9 ) },{ AV_PIX_FMT_GBRP9BE,      MKTAG( 9 , 00 , '3', 'G') },{ AV_PIX_FMT_GBRP10LE,     MKTAG('G', '3', 00 , 10 ) },{ AV_PIX_FMT_GBRP10BE,     MKTAG(10 , 00 , '3', 'G') },{ AV_PIX_FMT_GBRP12LE,     MKTAG('G', '3', 00 , 12 ) },{ AV_PIX_FMT_GBRP12BE,     MKTAG(12 , 00 , '3', 'G') },{ AV_PIX_FMT_GBRP14LE,     MKTAG('G', '3', 00 , 14 ) },{ AV_PIX_FMT_GBRP14BE,     MKTAG(14 , 00 , '3', 'G') },{ AV_PIX_FMT_GBRP16LE,     MKTAG('G', '3', 00 , 16 ) },{ AV_PIX_FMT_GBRP16BE,     MKTAG(16 , 00 , '3', 'G') },{ AV_PIX_FMT_GBRAP,        MKTAG('G', '4', 00 ,  8 ) },{ AV_PIX_FMT_GBRAP10LE,    MKTAG('G', '4', 00 , 10 ) },{ AV_PIX_FMT_GBRAP10BE,    MKTAG(10 , 00 , '4', 'G') },{ AV_PIX_FMT_GBRAP12LE,    MKTAG('G', '4', 00 , 12 ) },{ AV_PIX_FMT_GBRAP12BE,    MKTAG(12 , 00 , '4', 'G') },{ AV_PIX_FMT_GBRAP14LE,    MKTAG('G', '4', 00 , 14 ) },{ AV_PIX_FMT_GBRAP14BE,    MKTAG(14 , 00 , '4', 'G') },{ AV_PIX_FMT_GBRAP16LE,    MKTAG('G', '4', 00 , 16 ) },{ AV_PIX_FMT_GBRAP16BE,    MKTAG(16 , 00 , '4', 'G') },{ AV_PIX_FMT_XYZ12LE,      MKTAG('X', 'Y', 'Z' , 36 ) },{ AV_PIX_FMT_XYZ12BE,      MKTAG(36 , 'Z' , 'Y', 'X') },{ AV_PIX_FMT_BAYER_BGGR8,    MKTAG(0xBA, 'B', 'G', 8   ) },{ AV_PIX_FMT_BAYER_BGGR16LE, MKTAG(0xBA, 'B', 'G', 16  ) },{ AV_PIX_FMT_BAYER_BGGR16BE, MKTAG(16  , 'G', 'B', 0xBA) },{ AV_PIX_FMT_BAYER_RGGB8,    MKTAG(0xBA, 'R', 'G', 8   ) },{ AV_PIX_FMT_BAYER_RGGB16LE, MKTAG(0xBA, 'R', 'G', 16  ) },{ AV_PIX_FMT_BAYER_RGGB16BE, MKTAG(16  , 'G', 'R', 0xBA) },{ AV_PIX_FMT_BAYER_GBRG8,    MKTAG(0xBA, 'G', 'B', 8   ) },{ AV_PIX_FMT_BAYER_GBRG16LE, MKTAG(0xBA, 'G', 'B', 16  ) },{ AV_PIX_FMT_BAYER_GBRG16BE, MKTAG(16,   'B', 'G', 0xBA) },{ AV_PIX_FMT_BAYER_GRBG8,    MKTAG(0xBA, 'G', 'R', 8   ) },{ AV_PIX_FMT_BAYER_GRBG16LE, MKTAG(0xBA, 'G', 'R', 16  ) },{ AV_PIX_FMT_BAYER_GRBG16BE, MKTAG(16,   'R', 'G', 0xBA) },/* quicktime */{ AV_PIX_FMT_YUV420P, MKTAG('R', '4', '2', '0') }, /* Radius DV YUV PAL */{ AV_PIX_FMT_YUV411P, MKTAG('R', '4', '1', '1') }, /* Radius DV YUV NTSC */{ AV_PIX_FMT_UYVY422, MKTAG('2', 'v', 'u', 'y') },{ AV_PIX_FMT_UYVY422, MKTAG('2', 'V', 'u', 'y') },{ AV_PIX_FMT_UYVY422, MKTAG('A', 'V', 'U', 'I') }, /* FIXME merge both fields */{ AV_PIX_FMT_UYVY422, MKTAG('b', 'x', 'y', 'v') },{ AV_PIX_FMT_YUYV422, MKTAG('y', 'u', 'v', '2') },{ AV_PIX_FMT_YUYV422, MKTAG('y', 'u', 'v', 's') },{ AV_PIX_FMT_YUYV422, MKTAG('D', 'V', 'O', 'O') }, /* Digital Voodoo SD 8 Bit */{ AV_PIX_FMT_RGB555LE,MKTAG('L', '5', '5', '5') },{ AV_PIX_FMT_RGB565LE,MKTAG('L', '5', '6', '5') },{ AV_PIX_FMT_RGB565BE,MKTAG('B', '5', '6', '5') },{ AV_PIX_FMT_BGR24,   MKTAG('2', '4', 'B', 'G') },{ AV_PIX_FMT_BGR24,   MKTAG('b', 'x', 'b', 'g') },{ AV_PIX_FMT_BGRA,    MKTAG('B', 'G', 'R', 'A') },{ AV_PIX_FMT_RGBA,    MKTAG('R', 'G', 'B', 'A') },{ AV_PIX_FMT_RGB24,   MKTAG('b', 'x', 'r', 'g') },{ AV_PIX_FMT_ABGR,    MKTAG('A', 'B', 'G', 'R') },{ AV_PIX_FMT_GRAY16BE,MKTAG('b', '1', '6', 'g') },{ AV_PIX_FMT_RGB48BE, MKTAG('b', '4', '8', 'r') },{ AV_PIX_FMT_RGBA64BE,MKTAG('b', '6', '4', 'a') },{ AV_PIX_FMT_BAYER_RGGB16BE, MKTAG('B', 'G', 'G', 'R') },/* vlc */{ AV_PIX_FMT_YUV410P,     MKTAG('I', '4', '1', '0') },{ AV_PIX_FMT_YUV411P,     MKTAG('I', '4', '1', '1') },{ AV_PIX_FMT_YUV422P,     MKTAG('I', '4', '2', '2') },{ AV_PIX_FMT_YUV440P,     MKTAG('I', '4', '4', '0') },{ AV_PIX_FMT_YUV444P,     MKTAG('I', '4', '4', '4') },{ AV_PIX_FMT_YUVJ420P,    MKTAG('J', '4', '2', '0') },{ AV_PIX_FMT_YUVJ422P,    MKTAG('J', '4', '2', '2') },{ AV_PIX_FMT_YUVJ440P,    MKTAG('J', '4', '4', '0') },{ AV_PIX_FMT_YUVJ444P,    MKTAG('J', '4', '4', '4') },{ AV_PIX_FMT_YUVA444P,    MKTAG('Y', 'U', 'V', 'A') },{ AV_PIX_FMT_YUVA420P,    MKTAG('I', '4', '0', 'A') },{ AV_PIX_FMT_YUVA422P,    MKTAG('I', '4', '2', 'A') },{ AV_PIX_FMT_RGB8,        MKTAG('R', 'G', 'B', '2') },{ AV_PIX_FMT_RGB555LE,    MKTAG('R', 'V', '1', '5') },{ AV_PIX_FMT_RGB565LE,    MKTAG('R', 'V', '1', '6') },{ AV_PIX_FMT_BGR24,       MKTAG('R', 'V', '2', '4') },{ AV_PIX_FMT_BGR0,        MKTAG('R', 'V', '3', '2') },{ AV_PIX_FMT_RGBA,        MKTAG('A', 'V', '3', '2') },{ AV_PIX_FMT_YUV420P9LE,  MKTAG('I', '0', '9', 'L') },{ AV_PIX_FMT_YUV420P9BE,  MKTAG('I', '0', '9', 'B') },{ AV_PIX_FMT_YUV422P9LE,  MKTAG('I', '2', '9', 'L') },{ AV_PIX_FMT_YUV422P9BE,  MKTAG('I', '2', '9', 'B') },{ AV_PIX_FMT_YUV444P9LE,  MKTAG('I', '4', '9', 'L') },{ AV_PIX_FMT_YUV444P9BE,  MKTAG('I', '4', '9', 'B') },{ AV_PIX_FMT_YUV420P10LE, MKTAG('I', '0', 'A', 'L') },{ AV_PIX_FMT_YUV420P10BE, MKTAG('I', '0', 'A', 'B') },{ AV_PIX_FMT_YUV422P10LE, MKTAG('I', '2', 'A', 'L') },{ AV_PIX_FMT_YUV422P10BE, MKTAG('I', '2', 'A', 'B') },{ AV_PIX_FMT_YUV444P10LE, MKTAG('I', '4', 'A', 'L') },{ AV_PIX_FMT_YUV444P10BE, MKTAG('I', '4', 'A', 'B') },{ AV_PIX_FMT_YUV420P12LE, MKTAG('I', '0', 'C', 'L') },{ AV_PIX_FMT_YUV420P12BE, MKTAG('I', '0', 'C', 'B') },{ AV_PIX_FMT_YUV422P12LE, MKTAG('I', '2', 'C', 'L') },{ AV_PIX_FMT_YUV422P12BE, MKTAG('I', '2', 'C', 'B') },{ AV_PIX_FMT_YUV444P12LE, MKTAG('I', '4', 'C', 'L') },{ AV_PIX_FMT_YUV444P12BE, MKTAG('I', '4', 'C', 'B') },{ AV_PIX_FMT_YUV420P16LE, MKTAG('I', '0', 'F', 'L') },{ AV_PIX_FMT_YUV420P16BE, MKTAG('I', '0', 'F', 'B') },{ AV_PIX_FMT_YUV444P16LE, MKTAG('I', '4', 'F', 'L') },{ AV_PIX_FMT_YUV444P16BE, MKTAG('I', '4', 'F', 'B') },/* special */{ AV_PIX_FMT_RGB565LE,MKTAG( 3 ,  0 ,  0 ,  0 ) }, /* flipped RGB565LE */{ AV_PIX_FMT_YUV444P, MKTAG('Y', 'V', '2', '4') }, /* YUV444P, swapped UV */{ AV_PIX_FMT_NONE, 0 },
};

下面列一下可能用到的命令行测试指令：

# gstreamer 指令，注意分辨率和帧率要摄像头支持的，否则会失败# 打开摄像头并显示视频
gst-launch-1.0 v4l2src device=/dev/video9 ! video/x-raw,format=YUY2,width=640,height=480,framerate=30/1 ! videoconvert ! ximagesink# 打开摄像头并显示视频
gst-launch-1.0 -v v4l2src device=/dev/video9 ! "video/x-raw, format=(string)YUY2,width=(int)640, height=(int)480, framerate=(fraction)30/1" ! videoconvert ! kmssink

# 显示USB
lsusb
# 显示所有视频设备
ls /dev/video*
ll /dev/video*
# 显示所有摄像头
v4l2-ctl --list-devices
# 显示摄像头支持的格式和分辨率
v4l2-ctl --device=/dev/video9 --list-formats-ext
# 查看支持的可调参数
v4l2-ctl -d /dev/video9 --list-ctrls

部分指令效果记录

# lsusb
Bus 005 Device 001: ID 1d6b:0002
Bus 003 Device 001: ID 1d6b:0001
Bus 001 Device 001: ID 1d6b:0002
Bus 005 Device 018: ID 05e3:0610
Bus 005 Device 019: ID 2bc5:050b
Bus 008 Device 001: ID 1d6b:0003
Bus 006 Device 001: ID 1d6b:0003
Bus 004 Device 001: ID 1d6b:0001
Bus 002 Device 001: ID 1d6b:0002
Bus 005 Device 020: ID 2bc5:060b
Bus 007 Device 001: ID 1d6b:0002

# ll /dev/video*
crw-rw---- 1 root video 81,  0 Mar 20 14:09 /dev/video0
crw-rw---- 1 root video 81,  1 Mar 20 14:09 /dev/video1
crw-rw---- 1 root video 81, 10 Mar 20 14:50 /dev/video10
crw-rw---- 1 root video 81,  2 Mar 20 14:09 /dev/video2
crw-rw---- 1 root video 81,  3 Mar 20 14:09 /dev/video3
crw-rw---- 1 root video 81,  4 Mar 20 14:09 /dev/video4
crw-rw---- 1 root video 81,  5 Mar 20 14:09 /dev/video5
crw-rw---- 1 root video 81,  6 Mar 20 14:09 /dev/video6
crw-rw---- 1 root video 81,  7 Mar 20 14:09 /dev/video7
crw-rw---- 1 root video 81,  8 Mar 20 14:09 /dev/video8
crw-rw---- 1 root video 81,  9 Mar 20 14:50 /dev/video9
lrwxrwxrwx 1 root root       6 Mar 20 14:09 /dev/video-camera0 -> video0

# v4l2-ctl --list-devices
rkisp-statistics (platform: rkisp):/dev/video7/dev/video8rkisp_mainpath (platform:rkisp-vir0):/dev/video0/dev/video1/dev/video2/dev/video3/dev/video4/dev/video5/dev/video6/dev/media0USB 2.0 Camera: USB Camera (usb-xhci-hcd.0.auto-1.1):/dev/video9/dev/video10/dev/media1

# v4l2-ctl --device=/dev/video9 --list-formats-ext
ioctl: VIDIOC_ENUM_FMTType: Video Capture[0]: 'MJPG' (Motion-JPEG, compressed)Size: Discrete 2592x1944Interval: Discrete 0.040s (25.000 fps)Size: Discrete 2560x1440Interval: Discrete 0.040s (25.000 fps)Size: Discrete 1920x1080Interval: Discrete 0.017s (60.000 fps)Interval: Discrete 0.022s (45.000 fps)Interval: Discrete 0.033s (30.000 fps)Interval: Discrete 0.040s (25.000 fps)Interval: Discrete 0.050s (20.000 fps)Interval: Discrete 0.067s (15.000 fps)Interval: Discrete 0.100s (10.000 fps)Size: Discrete 1280x960Interval: Discrete 0.017s (60.000 fps)Interval: Discrete 0.022s (45.000 fps)Interval: Discrete 0.033s (30.000 fps)Interval: Discrete 0.040s (25.000 fps)Interval: Discrete 0.050s (20.000 fps)Interval: Discrete 0.067s (15.000 fps)Interval: Discrete 0.100s (10.000 fps)Size: Discrete 1280x720Interval: Discrete 0.017s (60.000 fps)Interval: Discrete 0.022s (45.000 fps)Interval: Discrete 0.033s (30.000 fps)Interval: Discrete 0.040s (25.000 fps)Interval: Discrete 0.050s (20.000 fps)Interval: Discrete 0.067s (15.000 fps)Interval: Discrete 0.100s (10.000 fps)Size: Discrete 640x480Interval: Discrete 0.017s (60.000 fps)Interval: Discrete 0.022s (45.000 fps)Interval: Discrete 0.033s (30.000 fps)Interval: Discrete 0.040s (25.000 fps)Interval: Discrete 0.050s (20.000 fps)Interval: Discrete 0.067s (15.000 fps)Interval: Discrete 0.100s (10.000 fps)Size: Discrete 320x240Interval: Discrete 0.017s (60.000 fps)Interval: Discrete 0.022s (45.000 fps)Interval: Discrete 0.033s (30.000 fps)Interval: Discrete 0.040s (25.000 fps)Interval: Discrete 0.050s (20.000 fps)Interval: Discrete 0.067s (15.000 fps)Interval: Discrete 0.100s (10.000 fps)[1]: 'YUYV' (YUYV 4:2:2)Size: Discrete 2592x1944Interval: Discrete 0.500s (2.000 fps)Size: Discrete 2560x1440Interval: Discrete 0.500s (2.000 fps)Size: Discrete 1920x1080Interval: Discrete 0.200s (5.000 fps)Size: Discrete 1280x960Interval: Discrete 0.200s (5.000 fps)Size: Discrete 1280x720Interval: Discrete 0.200s (5.000 fps)Size: Discrete 640x480Interval: Discrete 0.040s (25.000 fps)Size: Discrete 320x240Interval: Discrete 0.033s (30.000 fps)

# v4l2-ctl -d /dev/video9 --list-ctrlsbrightness 0x00980900 (int)    : min=-64 max=64 step=1 default=0 value=0contrast 0x00980901 (int)    : min=0 max=64 step=1 default=32 value=32saturation 0x00980902 (int)    : min=0 max=128 step=1 default=64 value=64hue 0x00980903 (int)    : min=-40 max=40 step=1 default=0 value=0white_balance_temperature_auto 0x0098090c (bool)   : default=1 value=1gamma 0x00980910 (int)    : min=72 max=500 step=1 default=100 value=100gain 0x00980913 (int)    : min=0 max=100 step=1 default=0 value=0power_line_frequency 0x00980918 (menu)   : min=0 max=2 default=1 value=1white_balance_temperature 0x0098091a (int)    : min=2800 max=6500 step=1 default=4600 value=4600 flags=inactivesharpness 0x0098091b (int)    : min=0 max=6 step=1 default=1 value=1backlight_compensation 0x0098091c (int)    : min=0 max=65535 step=1 default=0 value=0exposure_auto 0x009a0901 (menu)   : min=0 max=3 default=3 value=3exposure_absolute 0x009a0902 (int)    : min=1 max=5000 step=1 default=157 value=157 flags=inactiveexposure_auto_priority 0x009a0903 (bool)   : default=0 value=1