Tags: Python, Vision, Wireless communication

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In this tutorial, we’ll look at how to send a video stream from one machine to another using FFMPEG. Sending data between two devices, whatever it may be, is one of the major issues in connected objects (IoT). If yor’d like to create a connected camera that sends video to a remote machine, this article should interest you.

Installing ffmpeg

On a Linux machine

sudo apt-get install ffmpeg

On a Windows machine, please follow this procedure.

N.B.: if needed on a linux machine sudo apt-get install v4l-utils

Get the information yor need to stream Video

To create a video stream from one machine to another, the machines must be connected to the same network (Wifi or Ethernet).

First, yor need to obtain the IP address of the client machine (which receives the stream)

Enter a command terminal

ifconfig #pour une machine linux
ip addr # si ifconfig n'est pas disponible 

or

ipconfig #pour une machine windows

You should obtain an address of the form 192.168.X.X (in our case 192.168.1.67)

Then retrieve the video output. To list all the video inputs on a Linux machine

ls -l /dev/video*

lsusb #list usb devices

v4l2-ctl --list-devices #list video devices

These commands should help you identify the video output. In our case, /dev/video5

To list video outputs on a Windows machine, you can use ffmpeg

ffmpeg -list_devices true -f dshow -i dummy

In our case, video=”USB2.0 HD UVC WebCam “

Retrieve options and check formats and resolutions accepted by the camera

on Linux

v4l2-ctl -d /dev/video0 --list-formats

on Windows

ffmpeg -f dshow -list_options true -i video="USB2.0 HD UVC WebCam"

Once this data has been recorded, we can configure the streaming.

Creating a video stream with ffmpeg

To create a video stream, you need a sender (server) and a receiver (client) that will be connected to two terminals running on two different computers.

• linux server side

ffmpeg -re -f v4l2 -i /dev/video5 -r 10 -f mpegts udp://192.168.1.67:8554?pkt_size=1316

• Windows server side

ffmpeg -f dshow -i video="USB2.0 HD UVC WebCam" -r 10 -f mpegts udp://192.168.1.67:8554?pkt_size=1316

• customer side

ffplay udp://127.0.0.1:8554

N.B.: You can test streaming on a single machine using the IP address of the machine on which you are working and using two terminals, one for the server and one for the client.

To retrieve video statistics you can use the ffprobe command

ffprobe udp://127.0.0.1:8554

or, for more details,

ffprobe -show_format -show_streams udp://127.0.0.1:8554

Reduce video stream reception time between two machines

There is a delay of around 15 seconds between video transmission and reception. It may be useful to reduce this delay depending on the application.

On the server side, the parameters that affect transmission speed are:

• image size (e.g. -s 800×600)
• codec format conversion (e.g. -c:v libx264)
• number of frames per second or framerate (eg: -r 10)

Try to play with these parameters to reduce the delay while maintaining sufficient quality.

ffmpeg -re -thread_queue_size 64 -s800x600 -i

On the client side, there are various options that you can test from the documentation included in this discussion.

ffplay -fflags nobuffer -probesize 32 -sync ext -vf setpts=0 udp:

By modifying the options of the ffmpeg and ffplay commands, you can reduce the video stream delay from 15 to around 2 seconds.

Creating an HTTP stream with ffmpeg

It is possible to create an HTTP video server using VLC. The advantage of this method is that the video stream can be transmitted to any device.

• linux server side

ffmpeg -input_format h264 -video_size 1280x720 -framerate 30 -i /dev/video0 -vcodec copy -f mpegts -|vlc -I dummy - --sort='#std{access=http,mux=ts,dst=:8554}'

• customer side, you need to specify the IP address of the server

ffplay http://192.168.1.9:8554

Creating an RTSP stream with ffmpeg

It is possible to create an HTTP video server using VLC. The advantage of this method is that the video stream can be transmitted to any device.

• linux server side

ffmpeg -input_format h264 -video_size 1280x720 -framerate 30 -i /dev/video0 -vcodec copy -f mpegts -|vlc -I dummy - --sort='#rtp{sdp=rtsp://:8554/} --sort-all --sort-keep'

• customer side, you need to specify the IP address of the server

ffplay rtsp://192.168.1.9:8554/

Python script to start streaming

Here is a Python script that will allow you to test the different streaming methods as well as the ffmpeg parameters.

import subprocess

#UDP
#input client ip address here 192.168.1.9
stream_video="ffmpeg -input_format h264 -video_size 1280x720 -framerate 30 -i /dev/video0 -vcodec copy -f mpegts udp://192.168.1.9:8554?pkt_size=1316"
#on client side ffplay udp://127.0.0.1:8554

#HTTP
stream_video="ffmpeg -input_format h264 -video_size 1280x720 -framerate 30 -i /dev/video0 -vcodec copy -f mpegts -|vlc -I dummy - --sort='#std{access=http,mux=ts,dst=:8554}'"
#on client side ffplay http://192.168.1.73:8554

#RSTP
stream_video="ffmpeg -input_format h264 -video_size 1280x720 -framerate 30 -i /dev/video0 -vcodec copy -f mpegts -|vlc -I dummy - --sort='#rtp{sdp=rtsp://:8554/} --sort-all --sort-keep'"
#on client side ffplay rtsp://192.168.1.73:8554/ # don't forget / at the end

try:
	subprocess.call(stream_video,shell=True)
except:
	pass
print("Done")

Bonus: View FFMPEG’s video stream with OpenCV

Once the video stream has been established between the two machines, OpenCV can be used to read and display images from the UDP stream.

import cv2

def main(args):

	#cap = cv2.VideoCapture(0) #default camera
	cap = cv2.VideoCapture('udp://127.0.0.1:8554')
	#cap = cv2.VideoCapture('http://192.168.1.9:8554')
	#cap = cv2.VideoCapture('rtsp://192.168.1.9:8554/')

	while(True):
		ret, frame = cap.read()
		if ret: #necessary if packet is lost
			frame=cv2.resize(frame, (800, 600)) 
			cv2.imshow('Capturing',frame)
			
		if cv2.waitKey(1) & 0xFF == ord('q'): #click q to stop capturing
			break

	cap.release()
	cv2.destroyAllWindows()
	return 0

if __name__ == '__main__':
    import sys
    sys.exit(main(sys.argv))

Bonus2: Show time on video

To display the time on the video, we’re going to use ffmpeg’s drawtext filter, which uses certain text parameters

• fontfile: font used
• fontsize: text size
• fontcolor: corleur du texte

"drawtext=fontfile=/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans-Bold.ttf: text='%{localtime\:%T}': fontsize=24: fontcolor=white@0.8: x=7: y=460"

The filter is applied with the -vf tag. Here is the complete command

ffmpeg -input_format h264 -video_size 1280x720 -framerate 30 -i /dev/video0 -vf "drawtext=fontfile=/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans-Bold.ttf: text='%{localtime\:%T}': fontsize=24: fontcolor=white@0.8: x=7: y=460" -vcodec copy -f mpegts udp://192.168.1.9:8554?pkt_size=1316

In Python

stream_cmd="""ffmpeg -input_format h264 -video_size 1280x720 -framerate 30 -i /dev/video0 -vf "drawtext=fontfile=/usr/share/fonts/truetype/ttf-dejavu/DejaVuSans-Bold.ttf: text='%{localtime\:%T}': fontsize=24: fontcolor=white@0.8: x=7: y=460" -vcodec copy -f mpegts udp://192.168.1.9:8554?pkt_size=1316"""

Handy for imitating a CCTV camera or for comparing times from different cameras

Applications

• Acquisition of two synchronized video streams

Sources

• Install FFMPEG on Windows
• FFMPEG builds
• FFMPEG documentation
• Discussion FFMPEG delay
• Raspberry Pi as camera server