如何在Python中使用OpenCV存储网络摄像头视频

Question

我有一个Python脚本,可以读出我的网络摄像头并在窗口中显示.我现在想存储结果,所以按照本教程我编写了以下代码:

import cv2
import imutils
camera = cv2.VideoCapture(0)

# Define the codec and create VideoWriter object to save the video
fourcc = cv2.VideoWriter_fourcc(*'XVID')
video_writer = cv2.VideoWriter('output.avi', fourcc, 20.0, (640, 480))

while True:
    try:
        (grabbed, frame) = camera.read()  # grab the current frame
        frame = imutils.resize(frame, width=640, height=480)
        cv2.imshow("Frame", frame)  # show the frame to our screen
        key = cv2.waitKey(1) & 0xFF  # I don't really have an idea what this does, but it works..
        video_writer.write(frame)  # Write the video to the file system
    except KeyboardInterrupt:
        break

# cleanup the camera and close any open windows
camera.release()
video_writer.release()
cv2.destroyAllWindows()
print "\n\nBye bye\n"

这在一个新窗口中完美地显示了我的网络摄像头的实时视频片段.但是编写视频文件似乎失败了.它确实创建了一个名为的文件output.avi,但该文件为空(零字节),在命令行中我看到以下错误:

OpenCV: Frame size does not match video size.
OpenCV: Frame size does not match video size.
OpenCV: Frame size does not match video size.
etc.

我清楚地将帧大小调整到我要保存视频的大小(640x480),所以我不确定为什么它不匹配.

当我再次运行脚本时(所以在这种情况下空白output.avi已存在),它会显示以下错误:

2017-04-17 10:57:14.147 Python[86358:5848730] AVF: AVAssetWriter status: Cannot Save
2017-04-17 10:57:14.332 Python[86358:5848730] mMovieWriter.status: 3. Error: Cannot Save
2017-04-17 10:57:14.366 Python[86358:5848730] mMovieWriter.status: 3. Error: Cannot Save
2017-04-17 10:57:14.394 Python[86358:5848730] mMovieWriter.status: 3. Error: Cannot Save
etc.

在教程中,它说四位数的FourCC代码用于指定视频编解码器,它取决于平台,可用代码列表可以在fourcc.org中找到.我在OSX上,所以我尝试了一堆不同的编解码器代码:DIVX,XVID,MJPG,X264,WMV1,WMV2.但不幸的是,它们都不适合我.他们都给出了相同的错误,除了MJPG,这给了我以下错误:

OpenCV Error: Assertion failed (img.cols == width && img.rows == height && channels == 3) in write, file /tmp/opencv3-20170216-77040-y1hrk1/opencv-3.2.0/modules/videoio/src/cap_mjpeg_encoder.cpp, line 829
Traceback (most recent call last):
  File "store_video.py", line 15, in <module>
    video_writer.write(frame)  # Write the video to the file system
cv2.error: /tmp/opencv3-20170216-77040-y1hrk1/opencv-3.2.0/modules/videoio/src/cap_mjpeg_encoder.cpp:829: error: (-215) img.cols == width && img.rows == height && channels == 3 in function write

有人知道这里有什么问题吗？欢迎所有提示!

Answer 1

这可能是因为您使用AVFoundation构建了OpenCV,并且它不支持XVID或其他编解码器.你可以尝试mp4v和m4v扩展.

import cv2
camera = cv2.VideoCapture(0)

# Define the codec and create VideoWriter object to save the video
fourcc = cv2.VideoWriter_fourcc('m','p','4','v')
video_writer = cv2.VideoWriter('output.m4v', fourcc, 30.0, (640, 480))

while True:
        (grabbed, frame) = camera.read()  # grab the current frame
        frame = cv2.resize(frame, (640,480))
        cv2.imshow("Frame", frame)  # show the frame to our screen
        key = cv2.waitKey(33) & 0xFF  # I don't really have an idea what this does, but it works..
        video_writer.write(frame)  # Write the video to the file system
        if key==27:
            break;

# cleanup the camera and close any open windows
camera.release()
video_writer.release()
cv2.destroyAllWindows()
print("\n\nBye bye\n")

另一方面,错误

OpenCV Error: Assertion failed (img.cols == width && img.rows == height && channels == 3) in write, file /tmp/opencv3-20170216-77040-y1hrk1/opencv-3.2.0/modules/videoio/src/cap_mjpeg_encoder.cpp, line 829

意味着你搞砸了维度

frame = imutils.resize(frame, width=640, height=480)

您可以尝试cv2.resize我在我的代码中使用.cv2已经可以执行此操作时无需使用其他库.