如何使用openCV和Logitech C920使python记录每秒30帧或60帧

Question

我试图录制720p，60 FPS或1080p，30 FPS的视频，但是当在python上使用C920网络摄像头和OpenCV时，我只能在720p上获得大约10 fps，在1080p上只能获得5fps。

我为openCV尝试了很多不同的设置，但没有改变输出的FPS。

import cv2
import time
FPS = 0

cap = cv2.VideoCapture(0)
fourcc = cv2.VideoWriter_fourcc(*'MJPG')

if(not cap.isOpened()):
    exit()

cap.set(cv2.CAP_PROP_FOURCC, fourcc);
cap.open(cv2.CAP_ANY);
cap.set(cv2.CAP_PROP_CONVERT_RGB, 0);
cap.set(cv2.CAP_PROP_FRAME_WIDTH, 1280)
cap.set(cv2.CAP_PROP_FRAME_HEIGHT, 720)
cap.set(cv2.CAP_PROP_FPS, 60)

last = time.time()

for i in range(0,100):
    before = time.time()
    rval, frame = cap.read()
    now = time.time()
    print("cap.read() took: " + str(now - before))
    if(now - last >= 1):
        print(FPS)
        last = now
        FPS = 0
    else:
        FPS += 1
cap.release()

我希望它输出60fps，但它只能提供9或10 fps

Answer 1

你可以使用cv2.VideoWriter()。这是函数头

cv2.VideoWriter([filename, fourcc, fps, frameSize[, isColor]])

例如，将FPS设置为30

cv2.VideoWriter('output.avi', self.codec, 30, (frame_width, frame_height))

这是一个用于从网络摄像头流式传输和记录帧的小部件。

from threading import Thread
import cv2

class WebcamRecordWidget(object):
    def __init__(self, src=0):
        # Create a VideoCapture object
        self.capture = cv2.VideoCapture(src)

        # Default resolutions of the frame are obtained (system dependent)
        self.frame_width = int(self.capture.get(3))
        self.frame_height = int(self.capture.get(4))

        # Set up codec and output video settings
        self.codec = cv2.VideoWriter_fourcc('M','J','P','G')
        self.output_video = cv2.VideoWriter('output.avi', self.codec, 30, (self.frame_width, self.frame_height))

        # Start the thread to read frames from the video stream
        self.thread = Thread(target=self.update, args=())
        self.thread.daemon = True
        self.thread.start()

    def update(self):
        # Read the next frame from the stream in a different thread
        while True:
            if self.capture.isOpened():
                (self.status, self.frame) = self.capture.read()

    def show_frame(self):
        # Display frames in main program
        if self.status:
            cv2.imshow('frame', self.frame)

        # Press Q on keyboard to stop recording
        key = cv2.waitKey(1)
        if key == ord('q'):
            self.capture.release()
            self.output_video.release()
            cv2.destroyAllWindows()
            exit(1)

    def save_frame(self):
        # Save obtained frame into video output file
        self.output_video.write(self.frame)

if __name__ == '__main__':
    webcam_record_widget = WebcamRecordWidget()
    while True:
        try:
            webcam_record_widget.show_frame()
            webcam_record_widget.save_frame()
        except AttributeError:
            pass

Answer 2

OpenCV自动选择第一个可用的捕获后端(see here)。可能是它没有自动使用V4L2。

如果从源头构建，还要设置-D WITH_V4L=ON和-D WITH_LIBV4L=ON。

可能，OpenCV选择的像素格式不支持您想要的分辨率。在Linux上，您可以使用v4l2-ctl --list-formats-ext和v4l2-ctl --all查看设置。

要设置要使用的像素格式，请设置捕获的CAP_PROP_FOURCC属性：

capture = cv2.VideoCapture(cam_id, cv2.CAP_V4L2)
capture.set(cv2.CAP_PROP_FOURCC, cv2.VideoWriter_fourcc('M', 'J', 'P', 'G'))