python - 如何将视频流从一个 Python 传递到另一个？

问题描述

在我之前的帖子中，我们找到了一种将图像文件从一个 Python 传递到另一个 Python 的方法：将视频数据从一个 Python 脚本传递到另一个

我现在正在尝试传递视频（连续图像）：

写.py

import sys
import numpy as np
import cv2
from PIL import Image
import io
import time

while True:
    img = cv2.imread('cat.jpg')
    bimg = cv2.imencode('.jpg',img)[1]
    sys.stdout.buffer.write(bimg)
    sys.stdout.flush()
    time.sleep(1)

读取.py：

import sys
from PIL import Image
import io
import cv2
import numpy as np
from io import BytesIO
    
while True:
    data = sys.stdin.buffer.read()
    img_np = cv2.imdecode(np.frombuffer(BytesIO(data).read(), np.uint8), cv2.IMREAD_UNCHANGED)
    cv2.imshow('image', img_np)
    cv2.waitKey(0)

如果我将 write.py 数据输出到终端，它会打印出来。如果我手动将数据交给 read.py 读取。但是将它们放在一起（python3 write.py | python3 read.py），它就会挂起。write.py 只写一次，而 read.py 似乎永远不会得到它。

我的猜测是，读取代码正在等待写入代码“结束”，然后才打包数据包并将其称为图像。虽然如果是这样的话，我会认为做一个冲洗会解决它。

标签： pythonimagestreamstdoutcv2

我想我想通了。In read.py,sys.stdin.buffer.read()读取并等待stdin管道关闭，但由于循环而write.py从未真正关闭它。这个概念证明简化示例有效：stdoutwhile True

write.py

import sys
import time

sys.stdout.buffer.write(b"Hello world")
sys.stdout.buffer.flush()

# Note if we comment out the code bellow it works again
while True:
    # Keep this alive but don't have `while True:pass`
    # because my computer might crash :D
    time.sleep(10)

和read.py

import sys

with open("output.txt", "w") as file:
    file.write(sys.stdin.read())

这也将挂起，并且永远不会真正向"output.txt". 如果我们while True从代码中删除循环write.py将不再挂起"Hello World"并将被写入，"output.py"因为当write.py完成写入时它将关闭其进程并关闭管道。要解决此问题，我建议更改read.py为以下内容：

import sys

while True:
    with open("output.txt", "a") as file:
        file.write(sys.stdin.read(1))

解决方案：

write.py

import sys
import time

MAX_FILE_SIZE = 16 # bytes

msg = b"Hello world"

# Tell `reader.py` that it needs to read x number of bytes.
length = len(msg)
# We also need to tell `read.py` how many bytes it needs to read.
# This means that we have reached the same problem as before.
# To fix that issue we are always going to send the number of bytes but
# We are going to pad it with `0`s at the start.
# https://stackoverflow.com/a/339013/11106801
length = str(length).zfill(MAX_FILE_SIZE)
sys.stdout.buffer.write(length.encode())

sys.stdout.buffer.write(msg)
sys.stdout.buffer.flush()

# We also need to tell `read.py` that it was the last file that we send
# Sending `1` means that the file has ended
sys.stdout.buffer.write(b"1")
sys.stdout.buffer.flush()

# Note if we comment out the code bellow it works again
while True:
    # Keep this alive but don't have `while True:pass`
    # because my computer might crash :D
    time.sleep(10)

和read.py

import sys
import time

MAX_FILE_SIZE = 16 # bytes

while True:
    time.sleep(1) # Make sure `write.py` has sent the data
    # Read `MAX_FILE_SIZE` number of bytes and convert it to an int
    # So that we know the size of the file comming in
    length = int(sys.stdin.buffer.read(MAX_FILE_SIZE))
    time.sleep(1) # Make sure `write.py` has sent the data

    # Here you can switch to a different file every time `writer.py`
    # Sends a new file
    with open("output.txt", "wb") as file:
        file.write(sys.stdin.buffer.read(length))

    file_ended = sys.stdin.buffer.read(1)
    if file_ended == b"1":
        # File has ended
        break
    else:
        # We are going to start reading again for the next file:
        pass

编辑： 解决方案的工作原理如下：

发送文件大小
发送实际的文件数据
发送一个字节，告诉read.py它是否应该期待另一个文件

对于第 1 部分，我们只是将文件的长度编码为一个在前面用 0 填充的字符串。注意：确保MAX_FILE_SIZE大于最大文件的大小（大数字会稍微降低性能）。对于第 3 部分，如果我们发送一个"1"，则意味着没有更多文件要发送。否则reader.py将等待并接受下一个文件。所以write.py会变成：

from math import log
import time
import sys
import cv2


MAX_FILE_SIZE = 62914560 # bytes
MAX_FILE_SIZE = int(log(MAX_FILE_SIZE, 2)+1)


def write_file(buffer, data, last_file=False):
   # Tell `reader.py` that it needs to read x number of bytes.
   length = len(data)
   # We also need to tell `read.py` how many bytes it needs to read.
   # This means that we have reached the same problem as before.
   # To fix that issue we are always going to send the number of bytes but
   # We are going to pad it with `0`s at the start.
   # https://stackoverflow.com/a/339013/11106801
   length = str(length).zfill(MAX_FILE_SIZE)
   with open("output.txt", "w") as file:
      file.write(length)
   buffer.write(length.encode())

   # Write the actual data
   buffer.write(data)

   # We also need to tell `read.py` that it was the last file that we send
   # Sending `1` means that the file has ended
   buffer.write(str(int(last_file)).encode())
   buffer.flush()


while True:
    img = cv2.imread("img.jpg")
    bimg = cv2.imencode(".jpg", img)[1]
    # Call write_data
    write_file(sys.stdout.buffer, bimg, last_file=False)
    # time.sleep(1) # Don't need this

并将read.py成为：

from io import BytesIO
from math import log
import numpy as np
import time
import cv2
import sys


MAX_FILE_SIZE = 62914560 # bytes
MAX_FILE_SIZE = int(log(MAX_FILE_SIZE, 2)+1)


def read(buffer, number_of_bytes):
    output = b""
    while len(output) < number_of_bytes:
        output += buffer.read(number_of_bytes - len(output))
    assert len(output) == number_of_bytes, "An error occured."
    return output


def read_file(buffer):
    # Read `MAX_FILE_SIZE` number of bytes and convert it to an int
    # So that we know the size of the file comming in
    length = int(read(buffer, MAX_FILE_SIZE))

    # Here you can switch to a different file every time `writer.py`
    # Sends a new file
    data = read(buffer, length)

    # Read a byte so that we know if it is the last file
    file_ended = read(buffer, 1)

    return data, (file_ended == b"1")


while True:
    print("Reading file")
    data, last_file = read_file(sys.stdin.buffer)
    img_np = cv2.imdecode(np.frombuffer(BytesIO(data).read(), np.uint8),
                          cv2.IMREAD_UNCHANGED)
    cv2.imshow("image", img_np)
    cv2.waitKey(0)

    if last_file:
        break;

python - 如何将视频流从一个 Python 传递到另一个？

问题描述

解决方案

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