Python3 并行处理 opencv 视频帧

Question

我有一个视频文件，我需要逐帧处理，然后需要在帧中显示结果。目前，我正在按顺序进行处理并逐个显示帧。

现在我想并行处理帧，而不是按顺序处理。一旦处理了X个帧，那么cv2.imshow必须出现，并且必须以正确的顺序显示处理后的帧。

目前我的顺序代码如下所示

import cv2
import requests

def process_frame(bgr_image, jpg_as_text):
try:
# Post to api for processing and get the results
# result = requests.post("example.com", data={"jpg": jpg_as_text})
# Add results to bgr_image
# cv2.putText()
except Exception as e:
print(e)
pass
# Show the frame
cv2.imshow("frame", bgr_image)

video = cv2.VideoCapture("video.mp4")
i = 0

while video.isOpened():
ret, bgr_image = video.read()
if ret == True:
img_height, img_width, _ = bgr_image.shape
jpg_as_text = cv2.imencode(".jpg", bgr_image)[1].tostring()
process_frame(bgr_image, jpg_as_text)
print(i)
i += 1
else:
break
if cv2.waitKey(1) & 0xFF == ord("q"):
break
video.release()
cv2.destroyAllWindows()

现在我应该重构什么来进行并行处理，并在处理 X 个帧后预览帧。

Answer 1

OpenCV在其github存储库中有一个多线程视频处理的示例。

https://github.com/opencv/opencv/blob/master/samples/python/video_threaded.py

从multiprocessing.pool导入ThreadPool，并为每个CPU内核启动一个新线程。OpenCV有一个名为getNumberOfCPUs((的函数

例：

from __future__ import print_function
import numpy as np
import cv2 as cv
from multiprocessing.pool import ThreadPool
from collections import deque
from common import clock, draw_str, StatValue
import video

class DummyTask:
def __init__(self, data):
self.data = data
def ready(self):
return True
def get(self):
return self.data
if __name__ == '__main__':
import sys
print(__doc__)
try:
fn = sys.argv[1]
except:
fn = 0
cap = video.create_capture(fn)

def process_frame(frame, t0):
# some intensive computation...
frame = cv.medianBlur(frame, 19)
frame = cv.medianBlur(frame, 19)
return frame, t0
threadn = cv.getNumberOfCPUs()
pool = ThreadPool(processes = threadn)
pending = deque()
threaded_mode = True
latency = StatValue()
frame_interval = StatValue()
last_frame_time = clock()
while True:
while len(pending) > 0 and pending[0].ready():
res, t0 = pending.popleft().get()
latency.update(clock() - t0)
draw_str(res, (20, 20), "threaded      :  " +             str(threaded_mode))
draw_str(res, (20, 40), "latency        :  %.1f ms" %     (latency.value*1000))
draw_str(res, (20, 60), "frame interval :  %.1f ms" % (frame_interval.value*1000))
cv.imshow('threaded video', res)
if len(pending) < threadn:
ret, frame = cap.read()
t = clock()
frame_interval.update(t - last_frame_time)
last_frame_time = t
if threaded_mode:
task = pool.apply_async(process_frame, (frame.copy(), t))
else:
task = DummyTask(process_frame(frame, t))
pending.append(task)
ch = cv.waitKey(1)
if ch == ord(' '):
threaded_mode = not threaded_mode
if ch == 27:
break
cv.destroyAllWindows()

您应该能够使用该示例代码并将图像处理放在 process_frame 函数中。

在循环中添加一个计数器，并在计数 == X 时调用 cv2.imshow