我正在尝试从 Python 包装器为 OSX 下的 OpenCV 创建一个视频。我正在使用 python 2.7.1、opencv 2.3.1a 和来自 willowgarage 的 python 包装器，这些包装器随该版本的 opencv 一起提供。我有：
import cv,cv2
w = cv2.VideoWriter('foo.avi', cv.FOURCC('M','J','P','G'), 25, (100,100))
for i in range(100):
w.write(np.ones((100,100,3), np.uint8))
OpenCV 说
WARNING: Could not create empty movie file container.
Didn't successfully update movie file.
... [ 100 repetitions]
我不确定下一步该尝试什么
【问题讨论】：
关于这个主题有很多过时和不正确的在线指南——我想我几乎每一个都试过了。在查看了 Mac OSX 上基于 QTKit 的 VideoWriter 源代码实现后，我终于能够使用以下代码让 VideoWriter 输出有效的视频文件：
fps = 15
capSize = (1028,720) # this is the size of my source video
fourcc = cv2.cv.CV_FOURCC('m', 'p', '4', 'v') # note the lower case
self.vout = cv2.VideoWriter()
success = self.vout.open('output.mov',fourcc,fps,capSize,True)
要写一个图像帧（注意imgFrame的大小必须和上面的capSize一样，否则更新会失败）：
self.vout.write(imgFrame)
完成后请务必：
vout.release()
self.vout = None
这适用于 Mac OS X 10.8.5 (Mountain Lion)：不保证其他平台。我希望这个 sn-p 可以节省其他人的实验时间！
【讨论】：
'm', 'p', '4', 'v'。很多其他示例显示fourcc 使用的大写字母，我不知道它是否区分大小写。
我使用的是 macOS High Sierra 10.13.4、Python 3.6.5、OpenCV 3.4.1。
以下代码（来源：https://www.learnopencv.com/read-write-and-display-a-video-using-opencv-cpp-python/）打开摄像头，按“q”成功关闭窗口，并将视频保存为.avi格式。
请注意，您需要将其作为 .py 文件运行。如果在 Jupyter Notebook 中运行，窗口在关闭时会挂起，需要强制退出 Python 才能关闭窗口。
import cv2
import numpy as np
# Create a VideoCapture object
cap = cv2.VideoCapture(0)
# Check if camera opened successfully
if not cap.isOpened():
print("Unable to read camera feed")
# Default resolutions of the frame are obtained.The default resolutions are system dependent.
# We convert the resolutions from float to integer.
frame_width = int(cap.get(3))
frame_height = int(cap.get(4))
# Define the codec and create VideoWriter object.The output is stored in 'outpy.avi' file.
out = cv2.VideoWriter('outpy.avi',cv2.VideoWriter_fourcc('M','J','P','G'), 10, (frame_width,frame_height))
while True:
ret, frame = cap.read()
if ret:
# Write the frame into the file 'output.avi'
out.write(frame)
# Display the resulting frame
cv2.imshow('frame',frame)
# Press Q on keyboard to stop recording
if cv2.waitKey(1) & 0xFF == ord('q'):
break
# Break the loop
else:
break
# When everything done, release the video capture and video write objects
cap.release()
out.release()
# Closes all the frames
cv2.destroyAllWindows()
【讨论】：
在尝试了各种选项后，我发现我使用的 frame.size 不适合 VideoWriter 中指定的大小：因此将其设置为 iMac 1280x720 的默认值就可以了！
import numpy as np
import cv2
cap = cv2.VideoCapture(0)
# Define the codec and create VideoWriter object
fourcc = cv2.VideoWriter_fourcc('m', 'p', '4', 'v')
out = cv2.VideoWriter()
succes = out.open('output.mp4v',fourcc, 15.0, (1280,720),True)
while(cap.isOpened()):
ret, frame = cap.read()
if ret==True:
frame = cv2.flip(frame,0)
# write the flipped frame
out.write(frame)
cv2.imshow('frame',frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
else:
break
# Release everything if job is finished
cap.release()
out.release()
cv2.destroyAllWindows()
【讨论】：
这是“大小”问题。
import cv2
import time
filename = time.strftime("%m-%d-%H-%M-%S") + '.avi'
fps = 16
cap = cv2.VideoCapture(0)
#in this way it always works, because your get the right "size"
size = (int(cap.get(cv2.cv.CV_CAP_PROP_FRAME_WIDTH)),
int(cap.get(cv2.cv.CV_CAP_PROP_FRAME_HEIGHT)))
fourcc = cv2.cv.FOURCC('8', 'B', 'P', 'S') #works, large
out = cv2.VideoWriter(filename, fourcc, fps, size, True)
#in this way, you must set the "size" to your size,
#because you don't know the default "size" is right or not
#cap.set(3, 640)
#cap.set(4, 480)
#out = cv2.VideoWriter(filename, fourcc, fps, (640, 480), True)
while(cap.isOpened()):
ret, frame = cap.read()
if ret == True:
out.write(frame)
cv2.imshow('frame', frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break;
else:
print 'Error...'
break;
cap.release()
out.release()
cv2.destroyAllWindows()
【讨论】：
这是一个适用的版本：
使用brew install opencv 安装。
#!/usr/bin/env python3
import cv2
def main():
vc = cv2.VideoCapture()
if not vc.open('input.mp4'):
print('failed to open video capture')
return
fourcc = cv2.VideoWriter_fourcc(*'mp4v')
# Match source video features.
fps = vc.get(cv2.CAP_PROP_FPS)
size = (
int(vc.get(cv2.CAP_PROP_FRAME_WIDTH)),
int(vc.get(cv2.CAP_PROP_FRAME_HEIGHT)),
)
vw = cv2.VideoWriter()
if not vw.open('output.mp4', fourcc, fps, size):
print('failed to open video writer')
return
while True:
ok, frame = vc.read()
if not ok:
break
# Flip upside down.
frame = cv2.flip(frame, 0)
# Write processed frame.
vw.write(frame)
cv2.imshow('frame', frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
vc.release()
vw.release()
cv2.destroyAllWindows()
if __name__ == "__main__":
main()
【讨论】：
您的 ffmpeg 版本可能已过期。我在使用 ffmpeg 0.8 时遇到了类似的问题，升级到 ffmpeg 0.11 后它运行良好。
【讨论】：
以下是对我有用的@ToddStellanova 答案的变体：
def write_video(image_dir):
'''
Writes a video from a set of images in `image_dir`
'''
target = join('data/labelled-videos',
basename(image_dir) + '.mp4v')
codec = cv2.cv.CV_FOURCC('m', 'p', '4', 'v')
size = (256, 256)
v = cv2.VideoWriter(target, codec, 16, size)
for image_name in listdir(image_dir):
image_filename = join(image_dir, image_name)
arr = np.asarray(Image.open(image_filename))
assert arr.shape[:2] == size
v.write(arr)
【讨论】：
我的问题在于 frame_width 和 frame_height。请尝试以下操作：
import cv2
cap = cv2.VideoCapture(0)
# Define the codec and create VideoWriter object
fourcc = cv2.VideoWriter_fourcc(*'MJPG')
frame_width = int(cap.get(3))
frame_height = int(cap.get(4))
size = (frame_width, frame_height)
fps = 10
out = cv2.VideoWriter("output.avi", fourcc, fps, size)
while(cap.isOpened()):
ret, frame = cap.read()
if ret:
out.write(frame) # write the frame
cv2.imshow('frame', frame)
else:
break
if cv2.waitKey(1) == 27: # Esc
break
# Release everything if job is finished
cap.release()
out.release()
cv2.destroyAllWindows()
【讨论】：
这不是个好主意
你必须创建一个VideoWriter结构并使用方法WriteFrame：
import cv
cv.NamedWindow('cap', 1)
w = cv.CreateVideoWriter('test.avi',cv.CV_FOURCC('X','V','I','D'),25,(640,480))
cap = cv.CaptureFromCAM(0)
while(1):
img = cv.QueryFrame(cap)
cv.ShowImage('cap', img)
cv.WriteFrame(w, img)
if cv.WaitKey(1) == 27:
break
cv.DestroyWindow('cap')
【讨论】：
感谢@TeddStellanova
这里是 XCode C++ 版本：
int fWidth = capture.get(CV_CAP_PROP_FRAME_WIDTH);
int fHeight = capture.get(CV_CAP_PROP_FRAME_HEIGHT);
string vid_path = path + "frames.mov";
VideoWriter vid(vid_path,CV_FOURCC('m','p','4','v'),30,Size(fWidth,fHeight),true);
【讨论】：