Flask如何在后端实时处理视频帧在前端展示
大气层煮月亮 2024-08-11 11:03:02 阅读 53
怎么样在前端->选择视频文件->点击上传视频后->后端实时分析上传的视频->在前端展示后端分析结果（视频，文本）
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咱们先看整看整体代码，有个大概的印象。
Flask后端代码
<code>'''
cljc车流检测Demo
'''
from pytz import timezone
from datetime import datetime
# 用于上传保存视频
@app.route('/upload', methods=['POST'])
def upload_video():
VIDEOS_FOLDER = 'static\Videos'
video = request.files['video']
video.save(os.path.join(VIDEOS_FOLDER, '视频1.mp4'))
return jsonify({'message': 'Video uploaded and saved successfully'}), 200
# 用于把后端处理的视频帧数据传输到前端展示
@app.route('/video_feed')
def video_feed():
return Response(generate_frames(),
mimetype='multipart/x-mixed-replace; boundary=frame')code>
# 处理函数
def generate_frames():
frame_Num = 1
max_cars = 0
video_path = './static/Videos/视频1.mp4' # 必须固定一个位置，用于存放上传的视频文件
cap = cv2.VideoCapture(video_path)
fps = cap.get(cv2.CAP_PROP_FPS)
carsCascade = cv2.CascadeClassifier("car_rear.xml")
while cap.isOpened():
success, frame = cap.read()
if not success:
break
cv2.putText(frame,"second:"+str(round(frame_Num/fps,2))+"s",
(0,100),cv2.FONT_HERSHEY_SIMPLEX,1,(255,0,255),1)
cars = carsCascade.detectMultiScale(frame[700:1280,0:720], 1.2,minSize=(10,10))
for (x, y, w, h) in cars: # 遍历所有汽车的区域
cv2.rectangle(frame[700:1280,0:720], (x, y), (x + w, y + h), (0, 0, 255), 2)
# ！！！！将每一帧转换为JPEG格式并以字节流方式返回，！！！！！
ret, buffer = cv2.imencode('.jpg', frame)
frame = buffer.tobytes()
frame_Num+=1
yield (b'--frame\r\n'b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n')
@app.route('/') ###主页面路由
def index():
return render_template('index.html')
HTML前端代码
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en">code>
<head>
<link rel="stylesheet" type="text/css" href="/static/css/cljc.css">code>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />code>
<meta name="viewport" content="width=device-width, initial-scale=1.0">code>
<meta http-equiv="X-UA-Compatible" content="IE=edge">code>
<title>车流监测</title>
<style type="text/css">code>
body {
margin:0;
padding:0;
font-size:12px;
}
</style>
</head>
<body>
<div class="header">code>
<div><style>* { box-sizing: border-box; } body {margin: 0;}
.c14101{padding:10px;
text-align:center;
font-weight:600;
color:#ffffff;
font-family:"Microsoft Yahei", sans-serif;
background-image:url(/static/img/bg3.jpg);
background-repeat:repeat;
background-position:left top;
background-attachment:scroll;
background-size:auto;}</style>
<div id="ib1w" class="c14101">车流监测</div></div>code>
</div>
<div class="colmask threecol">code>
<div class="colmid">code>
<div class="colleft">code>
<div class="col1">code>
<div>
<style>* {
box-sizing: border-box;
} body {margin: 0;}
.c14101{padding:10px;
text-align:center;
font-weight:600;
color:#ffffff;
font-family:"Microsoft Yahei", sans-serif;
background-image:url(/static/img/bg1.jpg);
background-repeat:repeat;
background-position:left top;background-attachment:scroll;
background-size:auto;}
.htmlpage-row{display:table;
padding-top:10px;
padding-right:10px;
padding-bottom:10px;
padding-left:10px;
width:100%;}
.htmlpage-cell{
width:8%;
display:table-cell;height:75px;}
.c4195{height:400px;width:950px;
text-align:center;
position:relative;}
@media (max-width: 768px){
.htmlpage-cell{width:100%;display:block;}}
.footer {
display: flex;
justify-content: center;
align-items: center;
height: 50; /* 设置合适的高度 */
}
#upload-form {
display: flex;
flex-direction: column;
/* align-items: center; */
}
</style>
<div class="htmlpage-row">code>
<!-- <div class="htmlpage-cell"></div> -->code>
<!-- <div class="htmlpage-cell">code>
<video allowfullscreen="allowfullscreen" class="c4195" src="/static/img/video2.webm" controls="controls"></video>code>
</div> -->
<img src="{ { url_for('video_feed') }}" width="600px" height=590px">code>
<!-- <div class="htmlpage-cell"></div> -->code>
</div>
</div>
</div>
<div class="col2"> code>
<div class="BoxConTop">当前帧数</div>code>
<input type="text" id="frameNumber" name="frameNumber" readonly style="margin-top: -100px;">code>
<div class="BoxConTop">当前车辆数</div>code>
<input type="text" id="vehicleNumber" name="vehicleNumber" readonly style="margin-top: -100px;">code>
<div class="BoxConTop">车流量峰值</div>code>
<input type="text" id="peakTraffic" name="peakTraffic" readonly style="margin-top: -100px;">code>
</div>
<div class="col3">code>
<p>北京时间</p>
<input type="text" id="timeShow" name="timeWarning" readonly>code>
<p>安全预警栏</p>
<input type="text" id="safetyWarning" name="safetyWarning" readonly>code>
</div>
</div>
</div>
</div>
</div>
<div class="footer">code>
<form id="upload-form">code>
<input type="file" id="video" name="video" accept="video/*">code>
<button type="submit">上传视频</button>code>
</form>
</div>
<script src="https://cdn.socket.io/4.0.1/socket.io.min.js"></script>code>
<script>
var socket = io();
socket.on('update_data', function(data) {
document.getElementById('frameNumber').value = data.frame_Num;
document.getElementById('vehicleNumber').value = data.car_number;
document.getElementById('peakTraffic').value = data.max_cars;
document.getElementById('timeShow').value = data.timeShow;
document.getElementById('safetyWarning').value = data.safetyWarning;
});
</script>
</body>
<script>
document.getElementById('upload-form').addEventListener('submit', async (e) => {
e.preventDefault();
const formData = new FormData(e.target);
const response = await fetch('/upload', { method: 'POST', body: formData });
const data = await response.json();
console.log(data.message);
});
document.getElementById('play-btn').addEventListener('click', () => {
const videoFrame = document.getElementById('video-frame');
const source = new EventSource('/play');
source.onmessage = (event) => {
videoFrame.src = event.data;
};
});
</script>
</html>
代码可以创建一个.py文件，在编译软件（vscode,pycharm）中打开，这样看起来比较清晰。
video_path = './static/Videos/视频1.mp4'
必须固定一个位置，这个位置是upload路由从前端传输过来视频数据，保存的地址，上面是处理函数generate_frames()里面读取的步骤。
下面是保存的步骤,在upload_video()路由：
video.save(os.path.join(VIDEOS_FOLDER, '视频1.mp4')) #固定保存视频的地方，
二、前后端代码结合讲解
实现上传视频并保存在指定路径的功能！
@app.route('/upload', methods=['POST'])
def upload_video():
VIDEOS_FOLDER = 'static\Videos'
video = request.files['video']
video.save(os.path.join(VIDEOS_FOLDER, '视频1.mp4')) #固定保存视频的地方，
return jsonify({'message': 'Video uploaded and saved successfully'}), 200
<div class="footer">code>
<form id="upload-form">code>
<input type="file" id="video" name="video" accept="video/*">code>
<button type="submit">上传视频</button>code>
</form>
</div>
↓
传输在后端处理好的视频帧数据到前端展示
@app.route('/video_feed')
def video_feed():
return Response(generate_frames(),
mimetype='multipart/x-mixed-replace; boundary=frame')code>
# 处理函数
def generate_frames():
frame_Num = 1
max_cars = 0
video_path = './static/Videos/视频1.mp4' # 必须固定一个位置，用于存放上传的视频文件
cap = cv2.VideoCapture(video_path)
fps = cap.get(cv2.CAP_PROP_FPS)
carsCascade = cv2.CascadeClassifier("car_rear.xml")
while cap.isOpened():
success, frame = cap.read()
if not success:
break
cv2.putText(frame,"second:"+str(round(frame_Num/fps,2))+"s",
(0,100),cv2.FONT_HERSHEY_SIMPLEX,1,(255,0,255),1)
cars = carsCascade.detectMultiScale(frame[700:1280,0:720], 1.2,minSize=(10,10))
for (x, y, w, h) in cars: # 遍历所有汽车的区域
cv2.rectangle(frame[700:1280,0:720], (x, y), (x + w, y + h), (0, 0, 255), 2)
# ！！！！将每一帧转换为JPEG格式并以字节流方式返回，！！！！！
ret, buffer = cv2.imencode('.jpg', frame)
frame = buffer.tobytes()
frame_Num+=1
yield (b'--frame\r\n'b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n')
这是最关键的，其余都是处理函数。最后这一步将每一帧数据转换为了JPEG的格式并以字节流的方式返回。
# ！！！！将每一帧转换为JPEG格式并以字节流方式返回，！！！！！
# 1.转换为JPEG格式
ret, buffer = cv2.imencode('.jpg', frame)
# 2.转换为字节流
frame = buffer.tobytes()
# 3.通过路由函数发送给前端
yield (b'--frame\r\n'b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n')
yield (b'--frame\r\n'b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n')
通过上面这个方法yield（），把转换好的图像以字节流的方式传送给前端，那么前端如何接收到呢？这很简单，
<div class="htmlpage-row">code>
<img src="{ { url_for('video_feed') }}" width="600px" height=590px">code>
</div>
前端HTML：“接收来自后端路由video_feed（）函数传过来的参数。”后端FLASK：“yield（）通过video_feed（）函数发送数据给前端。”
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