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python处理内存中字节流形式的视频
在使用python的streamlit库处理上传的文件时碰到一个问题，文件上传后是以字节数组的形式存在内存中，我在后续需要使用cv2库逐帧操作上传的视频，这里就产生一个问题，cv2怎么读取到内存中字节形式的视频？ 经过多次查找，发现可以使用ffmpeg从内存中将字节流解码，然后再由cv2处理。
代码如下：
import streamlit as st
# streamlit中上传文件的函数
@st.cache(allow_output_mutation=True,show_spinner=False)
def load_local_video(uploaded_video):
bytes_data = uploaded_video.getvalue()
print(uploaded_video.name)
return bytes_data
uploaded_video = st.sidebar.file_uploader(" ")
video = load_local_video(uploaded_video)
处理逻辑就是使用ffprobe获取字节流中内存相关信息，然后使用ffmpeg解码。随后从字节流中逐帧获取视频。
import numpy as np
import cv2
import io
import subprocess as sp
import threading
import json
from functools import partial
import shlex
# Write to stdin in chunks of 1024 bytes.
def writer(stream,process):
for chunk in iter(partial(stream.read, 1024),b''):
process.stdin.write(chunk)
try:
process.stdin.close()
except (BrokenPipeError):
pass # For unknown reason there is a Broken Pipe Error when executing FFprobe.
def do(video):
bytes_stream = io.BytesIO(video)
#执行子进程并定到输入输出的接口，这里使用ffprobe检测视频的信息
# 注意，这里的路径是我本地的路径，运行代码的时候需要更改路径，并且确保你的电脑装上了ffmpeg
process = sp.Popen(shlex.split('E:/ffmpeg-4.3.1-2020-11-19-essentials_build/bin/ffprobe -v error -i pipe: -select_streams v -print_format json -show_streams'), stdin=sp.PIPE, stdout=sp.PIPE, bufsize=10**8)
pthread = threading.Thread(target=writer,args=(bytes_stream,process))
pthread.start()
pthread.join()
#从标准输入输出流中获取视频信息
in_bytes = process.stdout.read()
process.wait()
p = json.loads(in_bytes)
#得到视频的分辨率
width = (p['streams'][0])['width']
height = (p['streams'][0])['height']
bytes_stream.seek(0)
process = sp.Popen(shlex.split('E:/ffmpeg-4.3.1-2020-11-19-essentials_build/bin/ffmpeg -i pipe: -f rawvideo -pix_fmt bgr24 -an -sn pipe:'), stdin=sp.PIPE, stdout=sp.PIPE, bufsize=10**8)
thread = threading.Thread(target=writer,args=(bytes_stream,process))
thread.start()
#将视频解码完毕
all_bytes = process.stdout.read()#将视频字节从内存中读取出来
counter = len(all_bytes)/(width * height * 3)
#print(str(counter)+' 帧')
l = 0
my_bar = st.progress(0)
with st.spinner(text="视频检测中"):
while l |