I need to serve real-time graphs and I would like to deliver a mjpeg stream over http (so that it is easy to include the graphs in a web-page by using a plain tag).
Is it possible to create an mjpeg stream from multiple jpeg images, in realtime ?
My strategy is:
Output the correct http headers:
Cache-Control:no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0
Connection:close
Content-Type:multipart/x-mixed-replace;boundary=boundarydonotcross
Expires:Mon, 3 Jan 2000 12:34:56 GMT
Pragma:no-cache
Server:MJPG-Streamer/0.2
(got it from a curl -I {on a mjpeg-streamer instance}
, but this seems strange)
Simply yield the successive jpeg images binaries, taking care to:
prepend the correct headers at the beginning of the stream (as mjpeg-streamer does):
Content-Type: image/jpeg
Content-Length: 5427
X-Timestamp: 3927662.086099
append the boundary string at the end of each jpeg streams.
--boudary--
Questions:
Have you done that,
do you know a python module that does that,
do you think it would work,
have you got any advice ?
The main difference between H. 264 and MJPEG is that MJPEG only compresses individual frames of video, while H. 264 compresses across frames. MJPEG is the compilation of separately compressed JPEGs in a sequence, which leads to high quality outcome in terms of resolution.
VLC can play MJPEG files.
MJPEG is short for Motion-JPEG which is a means of storing video footage from IP cameras and digital camcorders. An MJPEG Movie consists of many JPEG images, one after another. Since JPEG is a compressed format, so too is MJPEG, providing a low file size when compared to image dimensions.
I got it working as a proof-of-concept: https://github.com/damiencorpataux/pymjpeg
For memory:
import os, time
from glob import glob
import sys
from BaseHTTPServer import HTTPServer, BaseHTTPRequestHandler
boundary = '--boundarydonotcross'
def request_headers():
return {
'Cache-Control': 'no-store, no-cache, must-revalidate, pre-check=0, post-check=0, max-age=0',
'Connection': 'close',
'Content-Type': 'multipart/x-mixed-replace;boundary=%s' % boundary,
'Expires': 'Mon, 3 Jan 2000 12:34:56 GMT',
'Pragma': 'no-cache',
}
def image_headers(filename):
return {
'X-Timestamp': time.time(),
'Content-Length': os.path.getsize(filename),
#FIXME: mime-type must be set according file content
'Content-Type': 'image/jpeg',
}
# FIXME: should take a binary stream
def image(filename):
with open(filename, "rb") as f:
# for byte in f.read(1) while/if byte ?
byte = f.read(1)
while byte:
yield byte
# Next byte
byte = f.read(1)
# Basic HTTP server
class MyHandler(BaseHTTPRequestHandler):
def do_GET(self):
self.send_response(200)
# Response headers (multipart)
for k, v in pymjpeg.request_headers().items():
self.send_header(k, v)
# Multipart content
for filename in glob('img/*'):
# Part boundary string
self.end_headers()
self.wfile.write(pymjpeg.boundary)
self.end_headers()
# Part headers
for k, v in pymjpeg.image_headers(filename).items():
self.send_header(k, v)
self.end_headers()
# Part binary
for chunk in pymjpeg.image(filename):
self.wfile.write(chunk)
def log_message(self, format, *args):
return
httpd = HTTPServer(('', 8001), MyHandler)
httpd.serve_forever()
You may use Flask framework to do this.
It is not only for mjpeg.
I adapted some code from here: https://blog.miguelgrinberg.com/post/video-streaming-with-flask
APP.py
#!/usr/bin/env python
from importlib import import_module
import os
from flask import Flask, render_template, Response
# import camera driver
if os.environ.get('CAMERA'):
Camera = import_module('camera_' + os.environ['CAMERA']).Camera
else:
from camera import Camera
# Raspberry Pi camera module (requires picamera package)
# from camera_pi import Camera
app = Flask(__name__)
@app.route('/')
def index():
"""Video streaming home page."""
return render_template('index.html')
def gen(camera):
"""Video streaming generator function."""
while True:
frame = camera.get_frame()
yield (b'--frame\r\n'
b'Content-Type: image/jpeg\r\n\r\n' + frame + b'\r\n')
@app.route('/video_feed')
def video_feed():
"""Video streaming route. Put this in the src attribute of an img tag."""
return Response(gen(Camera()),
mimetype='multipart/x-mixed-replace; boundary=frame')
if __name__ == '__main__':
app.run(host='0.0.0.0', threaded=True)
base_camera.py
import time
import threading
try:
from greenlet import getcurrent as get_ident
except ImportError:
try:
from thread import get_ident
except ImportError:
from _thread import get_ident
class CameraEvent(object):
"""An Event-like class that signals all active clients when a new frame is
available.
"""
def __init__(self):
self.events = {}
def wait(self):
"""Invoked from each client's thread to wait for the next frame."""
ident = get_ident()
if ident not in self.events:
# this is a new client
# add an entry for it in the self.events dict
# each entry has two elements, a threading.Event() and a timestamp
self.events[ident] = [threading.Event(), time.time()]
return self.events[ident][0].wait()
def set(self):
"""Invoked by the camera thread when a new frame is available."""
now = time.time()
remove = None
for ident, event in self.events.items():
if not event[0].isSet():
# if this client's event is not set, then set it
# also update the last set timestamp to now
event[0].set()
event[1] = now
else:
# if the client's event is already set, it means the client
# did not process a previous frame
# if the event stays set for more than 5 seconds, then assume
# the client is gone and remove it
if now - event[1] > 5:
remove = ident
if remove:
del self.events[remove]
def clear(self):
"""Invoked from each client's thread after a frame was processed."""
self.events[get_ident()][0].clear()
class BaseCamera(object):
thread = None # background thread that reads frames from camera
frame = None # current frame is stored here by background thread
last_access = 0 # time of last client access to the camera
event = CameraEvent()
def __init__(self):
"""Start the background camera thread if it isn't running yet."""
if BaseCamera.thread is None:
BaseCamera.last_access = time.time()
# start background frame thread
BaseCamera.thread = threading.Thread(target=self._thread)
BaseCamera.thread.start()
# wait until frames are available
while self.get_frame() is None:
time.sleep(0)
def get_frame(self):
"""Return the current camera frame."""
BaseCamera.last_access = time.time()
# wait for a signal from the camera thread
BaseCamera.event.wait()
BaseCamera.event.clear()
return BaseCamera.frame
@staticmethod
def frames():
""""Generator that returns frames from the camera."""
raise RuntimeError('Must be implemented by subclasses.')
@classmethod
def _thread(cls):
"""Camera background thread."""
print('Starting camera thread.')
frames_iterator = cls.frames()
for frame in frames_iterator:
BaseCamera.frame = frame
BaseCamera.event.set() # send signal to clients
time.sleep(0)
# if there hasn't been any clients asking for frames in
# the last 10 seconds then stop the thread
if time.time() - BaseCamera.last_access > 10:
frames_iterator.close()
print('Stopping camera thread due to inactivity.')
break
BaseCamera.thread = None
camera.py
#D:\gstreamer\1.0\x86\bin>gst-launch-1.0.exe multifilesrc loop=true start-index=0 stop-index=0 location=d:/python/temp.png ! decodebin ! identity sleep-time=1000000 ! videoconvert ! autovideosink
import shutil
import time
import os,sys
from PIL import Image, ImageFont, ImageDraw, ImageFile
from io import BytesIO
from base_camera import BaseCamera
im = Image.new("RGB", (300, 30), (220, 180, 180))
#im.format'JPEG'
dr = ImageDraw.Draw(im)
font = ImageFont.truetype(os.path.join("fonts", "msyh.ttf"), 16)
text =time.strftime("%m/%d %H:%M:%S") +u"这是一段测试文本。"
dr.text((10, 5), text, font=font, fill="#000000")
im.save("d://python/temp.jpg")
dr.rectangle((0,0,300,500),fill="#FFFFFF")
text =time.strftime("%m/%d %H:%M:%S") +u"这是一段测试文本。"
dr.text((10, 5),text, font=font, fill="#000000")
f = BytesIO()
f.name="sdf.jpg"
im.save(f,"JPEG")
f.seek(0)
f.close()
class Camera(BaseCamera):
"""An emulated camera implementation that streams a repeated sequence of
files 1.jpg, 2.jpg and 3.jpg at a rate of one frame penr second."""
imgs = [open(f + '.jpg', 'rb').read() for f in ['1', '2', '3']]
@staticmethod
def frames():
while True:
text =time.strftime("%m/%d %H:%M:%S") +u"这是一段测试文本。"
dr.rectangle((0,0,300,500),fill="#FFFFFF")
dr.text((10, 5), text, font=font, fill="#000000")
f = BytesIO()
im.save(f,'JPEG')
try :
im.save("d:/python/temp.jpg")
except :
print("Unexpected error:", sys.exc_info()[0])
pass
# shutil.copy("d:/python/temp2.png","d:/python/temp.png")
f.seek(0)
time.sleep(1)
yield f.read() #Camera.imgs[int(time.time()) % 3]
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