我正在使用opencv-python（版本4.4.0.46）的Python版本3.8.5来捕获我的IP摄像头流，但是我无法读取视频帧。这是我的代码：
import cv2
# cap = cv2.VideoCapture("rtsp://wowzaec2demo.streamlock.net/vod/mp4:BigBuckBunny_115k.mov")
cap = cv2.VideoCapture("rtsp://admin:xxx@xxx/Streaming/Channels/1")
print(cap.isOpened())
ret,frame = cap.read()
print(ret)
while ret:
ret,frame = cap.read()
print(ret)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
在我的代码中，当我使用IPC流时，"print(cap.isOpened())"返回True，而"cap.read()"返回False。但是，当它切换到"BigBuckBunny_115k"流时，一切正常，我可以获取帧图片。
有人可能会说你的IPC可能已损坏。但是，我尝试使用ffmpeg来捕获视频，可以轻松获取帧图片。我的代码：
ffmpeg -i "rtsp://admin:xxx@xxx/Streaming/Channels/1" -y -f image2 -r 1/1 img%03d.jpg
使用Python捕获视频时，我得到了像上面的“False”结果，但没有任何错误日志打印出来，这让我很难解决问题。所以我改用Java，并使用opencv-4.4.0.so作为库，我的代码如下：
VideoCapture videoCapture = new VideoCapture();
// set the exception mode true so that it can print stack trace when error
videoCapture.setExceptionMode(true);
boolean openStatus = videoCapture.open("rtsp://admin:xxx@xxx/Streaming/Channels/1");
log.info("open rtsp status: {}", openStatus);
int i = 0;
status = true;
while (openStatus && status) {
Mat mat = new Mat();
videoCapture.read(mat);
Imgcodecs.imwrite("../" + i + ".png", mat);
i++;
}
通过运行这段代码，我得到了一个异常：org.opencv.core.CvException: cv::Exception: OpenCV(4.4.0) /xxx/opencv-4.4.0/modules/videoio/src/cap.cpp:177: error: (-2:未指定错误) 无法打开 'rtsp://admin:xxx@xxx/Streaming/Channels/1' in function 'open'。 上面的异常日志并没有帮助解决问题，"-2:未指定错误"是什么意思？
忘了提一下，我的运行环境是CentOS 7.5（内核版本3.10.0-862.el7.x86_64）。然后我换了另一台具有相同opencv-python版本和CentOS版本的服务器。奇怪的是，在这台新服务器上，使用相同的opencv代码，我现在可以获取视频帧了。
第一个问题是，是否有相关信息可以参考？ 第二个问题是，如何排除这个问题。 第三个问题是，为什么在不同的服务器上表现不同，我的第一台服务器是否存在系统配置错误，比如网络配置？
更新于2021.01.07
感谢Antoine提供关于OpenCV后端的信息。我尝试使用以下代码打印python-opencv的构建信息。
import cv2
print(cv2.getBuildInformation())
在我拥有的两个服务器上（其中一个可以读取视频流，另一个不行），我得到了完全相同的控制台输出。这是输出内容：
General configuration for OpenCV 4.4.0 =====================================
Version control: 4.4.0-dirty
Platform:
Timestamp: 2020-11-03T00:52:03Z
Host: Linux 4.15.0-1077-gcp x86_64
CMake: 3.18.2
CMake generator: Unix Makefiles
CMake build tool: /bin/gmake
Configuration: Release
CPU/HW features:
Baseline: SSE SSE2 SSE3
requested: SSE3
Dispatched code generation: SSE4_1 SSE4_2 FP16 AVX AVX2 AVX512_SKX
requested: SSE4_1 SSE4_2 AVX FP16 AVX2 AVX512_SKX
SSE4_1 (15 files): + SSSE3 SSE4_1
SSE4_2 (1 files): + SSSE3 SSE4_1 POPCNT SSE4_2
FP16 (0 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 AVX
AVX (4 files): + SSSE3 SSE4_1 POPCNT SSE4_2 AVX
AVX2 (29 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2
AVX512_SKX (4 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2 AVX_512F AVX512_COMMON AVX512_SKX
C/C++:
Built as dynamic libs?: NO
C++ standard: 11
C++ Compiler: /usr/lib/ccache/compilers/c++ (ver 9.3.1)
C++ flags (Release): -Wl,-strip-all -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C++ flags (Debug): -Wl,-strip-all -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
C Compiler: /usr/lib/ccache/compilers/cc
C flags (Release): -Wl,-strip-all -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-comment -Wno-strict-overflow -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -O3 -DNDEBUG -DNDEBUG
C flags (Debug): -Wl,-strip-all -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-comment -Wno-strict-overflow -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -g -O0 -DDEBUG -D_DEBUG
Linker flags (Release): -Wl,--exclude-libs,libippicv.a -Wl,--exclude-libs,libippiw.a -L/root/ffmpeg_build/lib -Wl,--gc-sections -Wl,--as-needed
Linker flags (Debug): -Wl,--exclude-libs,libippicv.a -Wl,--exclude-libs,libippiw.a -L/root/ffmpeg_build/lib -Wl,--gc-sections -Wl,--as-needed
ccache: YES
Precompiled headers: NO
Extra dependencies: ade Qt5::Core Qt5::Gui Qt5::Widgets Qt5::Test Qt5::Concurrent /lib64/libpng.so /lib64/libz.so dl m pthread rt
3rdparty dependencies: ittnotify libprotobuf libjpeg-turbo libwebp libtiff libjasper IlmImf quirc ippiw ippicv
OpenCV modules:
To be built: calib3d core dnn features2d flann gapi highgui imgcodecs imgproc ml objdetect photo python3 stitching video videoio
Disabled: world
Disabled by dependency: -
Unavailable: java js python2 ts
Applications: -
Documentation: NO
Non-free algorithms: NO
GUI:
QT: YES (ver 5.15.0)
QT OpenGL support: NO
GTK+: NO
VTK support: NO
Media I/O:
ZLib: /lib64/libz.so (ver 1.2.7)
JPEG: libjpeg-turbo (ver 2.0.5-62)
WEBP: build (ver encoder: 0x020f)
PNG: /lib64/libpng.so (ver 1.5.13)
TIFF: build (ver 42 - 4.0.10)
JPEG 2000: build Jasper (ver 1.900.1)
OpenEXR: build (ver 2.3.0)
HDR: YES
SUNRASTER: YES
PXM: YES
PFM: YES
Video I/O:
DC1394: NO
FFMPEG: YES
avcodec: YES (58.109.100)
avformat: YES (58.61.100)
avutil: YES (56.60.100)
swscale: YES (5.8.100)
avresample: NO
GStreamer: NO
v4l/v4l2: YES (linux/videodev2.h)
Parallel framework: pthreads
Trace: YES (with Intel ITT)
Other third-party libraries:
Intel IPP: 2020.0.0 Gold [2020.0.0]
at: /tmp/pip-req-build-99ib2vsi/_skbuild/linux-x86_64-3.8/cmake-build/3rdparty/ippicv/ippicv_lnx/icv
Intel IPP IW: sources (2020.0.0)
at: /tmp/pip-req-build-99ib2vsi/_skbuild/linux-x86_64-3.8/cmake-build/3rdparty/ippicv/ippicv_lnx/iw
Lapack: NO
Eigen: NO
Custom HAL: NO
Protobuf: build (3.5.1)
OpenCL: YES (no extra features)
Include path: /tmp/pip-req-build-99ib2vsi/opencv/3rdparty/include/opencl/1.2
Link libraries: Dynamic load
Python 3:
Interpreter: /opt/python/cp38-cp38/bin/python (ver 3.8.6)
Libraries: libpython3.8.a (ver 3.8.6)
numpy: /tmp/pip-build-env-qru8fff1/overlay/lib/python3.8/site-packages/numpy/core/include (ver 1.17.3)
install path: python
Python (for build): /bin/python2.7
Java:
ant: NO
JNI: NO
Java wrappers: NO
Java tests: NO
Install to: /tmp/pip-req-build-99ib2vsi/_skbuild/linux-x86_64-3.8/cmake-install
-----------------------------------------------------------------
在打印件中，我找到了以下信息：
Video I/O:
DC1394: NO
FFMPEG: YES
avcodec: YES (58.109.100)
avformat: YES (58.61.100)
avutil: YES (56.60.100)
swscale: YES (5.8.100)
avresample: NO
GStreamer: NO
v4l/v4l2: YES (linux/videodev2.h)
看起来我的两台服务器都安装了FFMPEG，但没有安装GStreamer。所以，还有其他可能导致差异的原因吗？
顺便说一下，我已经尝试将API首选项传递给构造函数，如下所示：
cap = cv2.VideoCapture("rtsp://admin:xxx@xxx/Streaming/Channels/1", cv2.CAP_FFMPEG)
然而，传递参数并没有解决问题，我仍然无法读取视频帧。
cv2.getBuildInformation（）显示的版本是用于构建OpenCV的版本，可能与运行时使用的版本不同。如果您在一台服务器上自己构建它而在另一台服务器上没有构建，则可能会发生这种情况。 - antoine