关于CV_CAP_PROP_FRAME_WIDTH

关于CV_CAP_PROP_FRAME_WIDTH

宏定义

CV_CAP_PROP_FRAME_WIDTH是OpenCV库中的一个宏定义，用于获取视频帧的宽度属性。在OpenCV中，它被用作cv：：VideoCapture类的成员函数get（）的参数，用于获取视频帧的宽度。

具体来说，CV_CAP_PROP_FRAME_WIDTH表示视频帧的宽度属性，可以通过调用cv：：VideoCapture类的get（）函数来获取。例如，可以使用以下代码获取视频帧的宽度：

cv::VideoCapture cap("video.mp4"); // 打开视频文件
int frameWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); // 获取视频帧的宽度

在上述代码中，cap.get（CV_CAP_PROP_FRAME_WIDTH）将返回视频帧的宽度值。

enum VideoCaptureProperties {
       CAP_PROP_POS_MSEC       =0, //!< Current position of the video file in milliseconds.
       CAP_PROP_POS_FRAMES     =1, //!< 0-based index of the frame to be decoded/captured next.
       CAP_PROP_POS_AVI_RATIO  =2, //!< Relative position of the video file: 0=start of the film, 1=end of the film.
       CAP_PROP_FRAME_WIDTH    =3, //!< Width of the frames in the video stream.
       CAP_PROP_FRAME_HEIGHT   =4, //!< Height of the frames in the video stream.
       CAP_PROP_FPS            =5, //!< Frame rate.
       CAP_PROP_FOURCC         =6, //!< 4-character code of codec. see VideoWriter::fourcc .
       CAP_PROP_FRAME_COUNT    =7, //!< Number of frames in the video file.
       CAP_PROP_FORMAT         =8, //!< Format of the %Mat objects (see Mat::type()) returned by VideoCapture::retrieve().
                                   //!< Set value -1 to fetch undecoded RAW video streams (as Mat 8UC1).
       CAP_PROP_MODE           =9, //!< Backend-specific value indicating the current capture mode.
       CAP_PROP_BRIGHTNESS    =10, //!< Brightness of the image (only for those cameras that support).
       CAP_PROP_CONTRAST      =11, //!< Contrast of the image (only for cameras).
       CAP_PROP_SATURATION    =12, //!< Saturation of the image (only for cameras).
       CAP_PROP_HUE           =13, //!< Hue of the image (only for cameras).
       CAP_PROP_GAIN          =14, //!< Gain of the image (only for those cameras that support).
       CAP_PROP_EXPOSURE      =15, //!< Exposure (only for those cameras that support).
       CAP_PROP_CONVERT_RGB   =16, //!< Boolean flags indicating whether images should be converted to RGB. <br/>
                                   //!< *GStreamer note*: The flag is ignored in case if custom pipeline is used. It's user responsibility to interpret pipeline output.
       CAP_PROP_WHITE_BALANCE_BLUE_U =17, //!< Currently unsupported.
       CAP_PROP_RECTIFICATION =18, //!< Rectification flag for stereo cameras (note: only supported by DC1394 v 2.x backend currently).
       CAP_PROP_MONOCHROME    =19,
       CAP_PROP_SHARPNESS     =20,
       CAP_PROP_AUTO_EXPOSURE =21, //!< DC1394: exposure control done by camera, user can adjust reference level using this feature.
       CAP_PROP_GAMMA         =22,
       CAP_PROP_TEMPERATURE   =23,
       CAP_PROP_TRIGGER       =24,
       CAP_PROP_TRIGGER_DELAY =25,
       CAP_PROP_WHITE_BALANCE_RED_V =26,
       CAP_PROP_ZOOM          =27,
       CAP_PROP_FOCUS         =28,
       CAP_PROP_GUID          =29,
       CAP_PROP_ISO_SPEED     =30,
       CAP_PROP_BACKLIGHT     =32,
       CAP_PROP_PAN           =33,
       CAP_PROP_TILT          =34,
       CAP_PROP_ROLL          =35,
       CAP_PROP_IRIS          =36,
       CAP_PROP_SETTINGS      =37, //!< Pop up video/camera filter dialog (note: only supported by DSHOW backend currently. The property value is ignored)
       CAP_PROP_BUFFERSIZE    =38,
       CAP_PROP_AUTOFOCUS     =39,
       CAP_PROP_SAR_NUM       =40, //!< Sample aspect ratio: num/den (num)
       CAP_PROP_SAR_DEN       =41, //!< Sample aspect ratio: num/den (den)
       CAP_PROP_BACKEND       =42, //!< Current backend (enum VideoCaptureAPIs). Read-only property
       CAP_PROP_CHANNEL       =43, //!< Video input or Channel Number (only for those cameras that support)
       CAP_PROP_AUTO_WB       =44, //!< enable/ disable auto white-balance
       CAP_PROP_WB_TEMPERATURE=45, //!< white-balance color temperature
       CAP_PROP_CODEC_PIXEL_FORMAT =46,    //!< (read-only) codec's pixel format. 4-character code - see VideoWriter::fourcc . Subset of [AV_PIX_FMT_*](https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/raw.c) or -1 if unknown
       CAP_PROP_BITRATE       =47, //!< (read-only) Video bitrate in kbits/s
       CAP_PROP_ORIENTATION_META=48, //!< (read-only) Frame rotation defined by stream meta (applicable for FFmpeg back-end only)
       CAP_PROP_ORIENTATION_AUTO=49, //!< if true - rotates output frames of CvCapture considering video file's metadata  (applicable for FFmpeg back-end only) (https://github.com/opencv/opencv/issues/15499)
       CAP_PROP_HW_ACCELERATION=50, //!< (**open-only**) Hardware acceleration type (see #VideoAccelerationType). Setting supported only via `params` parameter in cv::VideoCapture constructor / .open() method. Default value is backend-specific.
       CAP_PROP_HW_DEVICE      =51, //!< (**open-only**) Hardware device index (select GPU if multiple available). Device enumeration is acceleration type specific.
       CAP_PROP_HW_ACCELERATION_USE_OPENCL=52, //!< (**open-only**) If non-zero, create new OpenCL context and bind it to current thread. The OpenCL context created with Video Acceleration context attached it (if not attached yet) for optimized GPU data copy between HW accelerated decoder and cv::UMat.
       CAP_PROP_OPEN_TIMEOUT_MSEC=53, //!< (**open-only**) timeout in milliseconds for opening a video capture (applicable for FFmpeg back-end only)
       CAP_PROP_READ_TIMEOUT_MSEC=54, //!< (**open-only**) timeout in milliseconds for reading from a video capture (applicable for FFmpeg back-end only)
       CAP_PROP_STREAM_OPEN_TIME_USEC =55, //<! (read-only) time in microseconds since Jan 1 1970 when stream was opened. Applicable for FFmpeg backend only. Useful for RTSP and other live streams
       CAP_PROP_VIDEO_TOTAL_CHANNELS = 56, //!< (read-only) Number of video channels
       CAP_PROP_VIDEO_STREAM = 57, //!< (**open-only**) Specify video stream, 0-based index. Use -1 to disable video stream from file or IP cameras. Default value is 0.
       CAP_PROP_AUDIO_STREAM = 58, //!< (**open-only**) Specify stream in multi-language media files, -1 - disable audio processing or microphone. Default value is -1.
       CAP_PROP_AUDIO_POS = 59, //!< (read-only) Audio position is measured in samples. Accurate audio sample timestamp of previous grabbed fragment. See CAP_PROP_AUDIO_SAMPLES_PER_SECOND and CAP_PROP_AUDIO_SHIFT_NSEC.
       CAP_PROP_AUDIO_SHIFT_NSEC = 60, //!< (read only) Contains the time difference between the start of the audio stream and the video stream in nanoseconds. Positive value means that audio is started after the first video frame. Negative value means that audio is started before the first video frame.
       CAP_PROP_AUDIO_DATA_DEPTH = 61, //!< (open, read) Alternative definition to bits-per-sample, but with clear handling of 32F / 32S
       CAP_PROP_AUDIO_SAMPLES_PER_SECOND = 62, //!< (open, read) determined from file/codec input. If not specified, then selected audio sample rate is 44100
       CAP_PROP_AUDIO_BASE_INDEX = 63, //!< (read-only) Index of the first audio channel for .retrieve() calls. That audio channel number continues enumeration after video channels.
       CAP_PROP_AUDIO_TOTAL_CHANNELS = 64, //!< (read-only) Number of audio channels in the selected audio stream (mono, stereo, etc)
       CAP_PROP_AUDIO_TOTAL_STREAMS = 65, //!< (read-only) Number of audio streams.
       CAP_PROP_AUDIO_SYNCHRONIZE = 66, //!< (open, read) Enables audio synchronization.
       CAP_PROP_LRF_HAS_KEY_FRAME = 67, //!< FFmpeg back-end only - Indicates whether the Last Raw Frame (LRF), output from VideoCapture::read() when VideoCapture is initialized with VideoCapture::open(CAP_FFMPEG, {CAP_PROP_FORMAT, -1}) or VideoCapture::set(CAP_PROP_FORMAT,-1) is called before the first call to VideoCapture::read(), contains encoded data for a key frame.
       CAP_PROP_CODEC_EXTRADATA_INDEX = 68, //!< Positive index indicates that returning extra data is supported by the video back end.  This can be retrieved as cap.retrieve(data, <returned index>).  E.g. When reading from a h264 encoded RTSP stream, the FFmpeg backend could return the SPS and/or PPS if available (if sent in reply to a DESCRIBE request), from calls to cap.retrieve(data, <returned index>).
#ifndef CV_DOXYGEN
       CV__CAP_PROP_LATEST
#endif
     };

//! Flags for cv::namedWindow
enum WindowFlags {
       WINDOW_NORMAL     = 0x00000000, //!< the user can resize the window (no constraint) / also use to switch a fullscreen window to a normal size.
       WINDOW_AUTOSIZE   = 0x00000001, //!< the user cannot resize the window, the size is constrainted by the image displayed.
       WINDOW_OPENGL     = 0x00001000, //!< window with opengl support.

       WINDOW_FULLSCREEN = 1,          //!< change the window to fullscreen.
       WINDOW_FREERATIO  = 0x00000100, //!< the image expends as much as it can (no ratio constraint).
       WINDOW_KEEPRATIO  = 0x00000000, //!< the ratio of the image is respected.
       WINDOW_GUI_EXPANDED=0x00000000, //!< status bar and tool bar
       WINDOW_GUI_NORMAL = 0x00000010, //!< old fashious way
    };

关于CV_CAP_PROP_FRAME_WIDTH问题的解决

此问题是OpenCV升级至4.x版本，对之前的写法不兼容的问题。
解决方法一：
将CV删掉，即：
CV_CAP_PROP_FRAME_WIDTH
改为
CAP_PROP_FRAME_WIDTH
同样的，第二个报错的
CV_CAP_PROP_FRAME_HEIGHT
改为
CAP_PROP_FRAME_HEIGHT
按这个方式改正后，问题就得到了解决

解决方法二：
CAP_PROP_FRAME_WIDTH =3,
CAP_PROP_FRAME_HEIGHT =4,
CAP_PROP_FPS =5,
WINDOW_AUTOSIZE = 0x00000001
CAP_PROP_FRAME_WIDTH、CAP_PROP_FRAME_HEIGHT、CAP_PROP_FPS、WINDOW_AUTOSIZE分别用3、4、5、0x00000001代替
按这个方式改正后，问题也得到了解决

解决方法三：
看代码的时候，有些前面有cv::的前缀，突然就想加个前缀cv::试试看
改为
cv::CAP_PROP_FRAME_WIDTH
按这个方式改正后，问题也得到了解决

当去掉CV_ 无效时，可以使用这个