OpenCV Video I/O 架構總覽

以下為 OpenCV Video IO 的架構總覽，以及可以使用的 backends

OpenCV: Video I/O with OpenCV Overview
https://docs.opencv.org/3.4.8/d0/da7/videoio_overview.html
裡面有一張架構圖，能夠比較了解 video io 整體的架構

https://docs.opencv.org/3.4.8/d4/d15/group__videoio__flags__base.html
這篇有列出VideoCaptureAPIs有哪些backends可以使用

cv::CAP_ANY = 0,
cv::CAP_VFW = 200,
cv::CAP_V4L = 200,
cv::CAP_V4L2 = CAP_V4L,
cv::CAP_FIREWIRE = 300,
cv::CAP_FIREWARE = CAP_FIREWIRE,
cv::CAP_IEEE1394 = CAP_FIREWIRE,
cv::CAP_DC1394 = CAP_FIREWIRE,
cv::CAP_CMU1394 = CAP_FIREWIRE,
cv::CAP_QT = 500,
cv::CAP_UNICAP = 600,
cv::CAP_DSHOW = 700,
cv::CAP_PVAPI = 800,
cv::CAP_OPENNI = 900,
cv::CAP_OPENNI_ASUS = 910,
cv::CAP_ANDROID = 1000,
cv::CAP_XIAPI = 1100,
cv::CAP_AVFOUNDATION = 1200,
cv::CAP_GIGANETIX = 1300,
cv::CAP_MSMF = 1400,
cv::CAP_WINRT = 1410,
cv::CAP_INTELPERC = 1500,
cv::CAP_OPENNI2 = 1600,
cv::CAP_OPENNI2_ASUS = 1610,
cv::CAP_GPHOTO2 = 1700,
cv::CAP_GSTREAMER = 1800,
cv::CAP_FFMPEG = 1900,
cv::CAP_IMAGES = 2000,
cv::CAP_ARAVIS = 2100,
cv::CAP_OPENCV_MJPEG = 2200,
cv::CAP_INTEL_MFX = 2300,
cv::CAP_XINE = 2400

CAP_VFW CAP_QT 在最新版已經不支持了，可以看看這筆的改動。

其他一些相關改動
videoio: drop obsolete backends  

https://github.com/opencv/opencv/pull/13060

videoio: remove cap_libv4l in favour of cap_v4l #13126

videoio: remove cap_libv4l in favour of cap_v4l