树莓派3B下OpenCV+GStreamer RTSP推流至VLC失败问题排查

在树莓派3B上尝试使用OpenCV和GStreamer实现视频推流，参考网上代码编写后遇到问题：代码中out.isOpened()始终返回False，但本地通过imshow可以正常显示视频，推流端无任何连接请求。

使用的Python代码 #

import cv2

cap = cv2.VideoCapture('sample-mp4-file.mp4')

# Get video dimensions
frame_width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
frame_height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
fps = int(cap.get(cv2.CAP_PROP_FPS))

pipeline = 'appsrc ! videoconvert ! videoscale ! video/x-raw,width=640,height=480 ! x264enc speed-preset=veryfast tune=zerolatency bitrate=800 ! rtspclientsink location=rtsp://localhost:8554/mystream '
out = cv2.VideoWriter(pipeline, cv2.CAP_GSTREAMER, 0, fps, (frame_width, frame_height))

print(out.isOpened())
print()

while cap.isOpened():
    ret, frame = cap.read()
    if ret:
        # Display the frame
        cv2.imshow('Video Stream', frame)
        out.write(frame)
        print(out.isOpened())

        if cv2.waitKey(int(1000/fps)) & 0xFF == ord('q'):
            break
    else:
        break

# Release everything if job is finished
cap.release()
out.release()

可正常运行的GStreamer命令 #

直接在命令行执行以下命令可实现正常推流：

gst-launch-1.0 filesrc location=sample-mp4-file.mp4 ! decodebin ! videoconvert ! videoscale ! video/x-raw,width=640,height=480 ! x264enc speed-preset=veryfast tune=zerolatency bitrate=800 ! rtspclientsink location=rtsp://localhost:8554/mystream

测试环境说明 #

测试所用MP4文件和RTSP流服务（mediamtx）均正常，正常推流时可通过PC端VLC观看视频。

排查结果 #

执行以下代码检查OpenCV编译配置：

import cv2
print(cv2.getBuildInformation())

输出显示OpenCV未启用GStreamer支持：

Video I/O:
    DC1394:                      NO
    FFMPEG:                      YES
      avcodec:                   YES (59.37.100)
      avformat:                  YES (59.27.100)
      avutil:                    YES (57.28.100)
      swscale:                   YES (6.7.100)
      avresample:                NO
    GStreamer:                   NO
    v4l/v4l2:                    YES (linux/videodev2.h)

当前进展 #

目前正在重新编译OpenCV以添加GStreamer支持，完成后将更新进展。

内容的提问来源于stack exchange，提问作者Christo Labuschagne