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• Matplotlib animation quality loss

  28 juin 2017, par Doe a

  I’m currently trying to use matplotlib to animate a grid using imshow. However, I am finding a fairly significant quality loss in the animation.

  Below is a simple animation that illustrates my issue fairly well. If you look at any particular frame of imagelist, you will see that there is no aliasing or gradient between colours. But if I then look at one frame of my animation, that is no longer the case. There is now a 4-5 pixel gradient between my blocks of colour. Does anyone know how I can get around this compression ? The file size of the animation doesn’t matter too much, as long as I can get a good quality animation.

  #Create list of images
  
  image=np.array([[[0,0,0],(0.7,0,0),(0,0,0),(0,0,0.8)]])
  
  imagelist=[]
  
  for i in range(0,100):
  
      image[0][1][0]=i/100
  
      imagelist.append(np.copy(image))
  
  
  
  #Create figure    
  
  fig = plt.figure()
  
  plt.axis('off')
  
  im = plt.imshow(imagelist[0], vmin=0, vmax=255,interpolation='none');
  
  
  
  #Animation
  
  def updatefig(j):
  
      im.set_array(imagelist[j])
  
      return [im]
  
  ani = animation.FuncAnimation(fig, updatefig, frames=range(len(imagelist)), interval=20, blit=False)
  
  
  
  #Save animation
  
  FFMpegWriter = animation.writers['ffmpeg']
  
  mywriter = FFMpegWriter(fps=30, bitrate=5000)
  
  ani.save("test.mp4", writer=mywriter,codec="libx264")

• Live video from raw tcp packets

  7 juin 2017, par benuuts

  we are trying to make a small python app that display a live video from sniffed packets using scapy and ffplay. This is part of our master degree research project. The goal is to make a proof of concept app that spies on video transimitted over tcp.
  We have a working script that writes into a .dat file and then we read it using ffplay. It works ok but have a lot of latency and we think we could do better : directly stream it into ffplay without the need to write raw data in a file.

  Here’s our script :

  from scapy.all import * 
  
  import os
  
  
  
  export_dat = open("data.dat", "a")
  
  
  
  def write_packet_raw(packet):
  
      export_dat.write(str(packet.getlayer(Raw)))
  
  
  
  def realtime_packet():
  
      p = sniff(iface="wlan0", filter="tcp and (port 5555)", count=5000, prn=write_packet_raw)
  
  
  
  realtime_packet()
  
  export_dat.close()

  And then we launch : ffplay -window_title Videostream -framedrop -infbuf -f h264 -i data.dat

  Any idea on how we can achieve that ? thanks.

• MPEG-DASH Livestreaming using ffmpeg, avconv, MP4Box and Dashjs

  28 avril 2017, par Sushant Mongia

  I’m working on delivering Live Streaming with DASH capabilities. Long story short, it’s a very crude testbed setup so I might be off the mark in some respects. I’m also posting this as a simple setup for the community and people out there struggling to look up a Live Streaming with DASH Tutorial.

  Setup :
  OS : Ubuntu 16.04
  Encoding Tools :
  ffmpeg : To record a livestream using a desktop webcam in mpeg2 format
  avconv : To convert mpeg2 to mpeg4 file format
  MP4Box : To DASH it, i.e. produce the .mpd, some conf files, seg_init and the segments
  Dashjs : Reference Client 2.4.1
  Server : Apache

  Process :
  I’ve written 3 bash scripts, with basically an infinite while loop in them, with ffmpeg , avconv and the MP4Box commands, one in each of them. I first run the ffmpeg script that records a video using the desktop webcam and then I run the avconv script that kills the ffmpeg command and converts the file from mpeg2 format to mpeg 4 format. Now since the ffmpeg command is in an infinite while loop, it restarts. Then I run the MP4Box command that DASH-es the avconv commands’ output. Then everything is sent to the DASHjs client and pretty much the whole setup gets repeated every 5 seconds.

  Commands :

  ---

  ffmpeg -f v4l2 -framerate 25 -video_size 640x480 -i /dev/video0 -f mpegts -codec:v mpeg1video -s 640x480 -b:v 1000k -bf 0 livestream  

  ---

  avconv -i livestream out.mp4  

  ---

  MP4Box command in a loop, MP4Box -dash-live 4000 -fps 24 -frag 6000 -profile dashavc264:live -dynamic -mpd-refresh 5000 -dash-ctx dashtest.txt -time-shift -1 -inter 0 -segment-name output-seg -bs-switching no out.mp4  

  Problem :
  The ffmpeg sends a chunk of 5 seconds (that’s due to the sleep command in my avconv bash script) and the MP4Box reads that 5 second chunk and loops that chunk. So when the next chunk comes in, newer segments are produced, but the player is still playing the older segments, typically just the very first few segments in a loop.

  Questions :
  1) Am I missing out on some core concept here ? Are the commands and their respective attributes with the right parameters and the right values ?
  2) I believe there should be a way to pipeline these processes in a better manner, should I be looking into writing a python script maybe ?

  Happy to provide more info ! Cheers