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• OpenCV Python, reading video from named-pipe

  29 février 2020, par BlueNut

  I am trying to achieve results as shown on the video (Method 3 using netcat) https://www.youtube.com/watch?v=sYGdge3T30o
  It is to stream video from raspberry pi to PC and process it using openCV and python.

  I use command

  raspivid -vf -n -w 640 -h 480 -o - -t 0 -b 2000000 | nc 192.168.1.137 8000

  to stream the video to my PC and then on the PC I created name pipe ’fifo’ and redirected the output

  nc -l -p 8000 -v > fifo

  then i am trying to read the pipe and display the result in the python script

  import cv2
  
  import subprocess as sp
  
  import numpy
  
  
  
  FFMPEG_BIN = "ffmpeg.exe"
  
  command = [ FFMPEG_BIN,
  
          '-i', 'fifo',             # fifo is the named pipe
  
          '-pix_fmt', 'bgr24',      # opencv requires bgr24 pixel format.
  
          '-vcodec', 'rawvideo',
  
          '-an','-sn',              # we want to disable audio processing (there is no audio)
  
          '-f', 'image2pipe', '-']    
  
  pipe = sp.Popen(command, stdout = sp.PIPE, bufsize=10**8)
  
  
  
  while True:
  
      # Capture frame-by-frame
  
      raw_image = pipe.stdout.read(640*480*3)
  
      # transform the byte read into a numpy array
  
      image =  numpy.frombuffer(raw_image, dtype='uint8')
  
      image = image.reshape((480,640,3))          # Notice how height is specified first and then width
  
      if image is not None:
  
          cv2.imshow('Video', image)
  
  
  
      if cv2.waitKey(1) & 0xFF == ord('q'):
  
          break
  
      pipe.stdout.flush()
  
  
  
  cv2.destroyAllWindows()

  But I got this error :

  Traceback (most recent call last):
  
    File "C:\Users\Nick\Desktop\python video stream\stream.py", line 19, in <module>
  
      image = image.reshape((480,640,3))          # Notice how height is specified first and then width
  
  ValueError: cannot reshape array of size 0 into shape (480,640,3)
  
  </module>

  It seems that the numpy array is empty, so any ideas to fix this ?

• FFmpeg with Pipe - how can I periodically grab real-time frames out of live streams in C# ?

  2 mars 2020, par BBy

  I am new to FFmpeg and C# and I want grab frames to do image processing with IP Camera.

  I have made the following C# class and I could get a single frame from IP Camera.

  class FFmpegHandler
  
      {
  
          public Process ffmpeg = new Process();
  
          public Image image;
  
  
  
          public Image init()
  
          {
  
              ffmpeg = new Process()
  
              {
  
                  StartInfo =
  
                  {
  
                      FileName = @"./ffmpeg/ffmpeg.exe",
  
                      //Arguments = "-i http://admin:@192.168.10.1/videostream.asf -an -f image2pipe -preset ultrafast -tune zerolatency -s 320x240 pipe:1", // Hangs
  
                      Arguments = "-i http://admin:@192.168.10.1/videostream.asf -vframes 1 -an -f image2pipe -preset ultrafast -tune zerolatency -s 320x240 pipe:1",
  
                      UseShellExecute = false,
  
                      RedirectStandardOutput = true,
  
                      RedirectStandardError = true,
  
                      CreateNoWindow = true,
  
                      WorkingDirectory = "./ffmpeg/"
  
                  }
  
              };
  
  
  
              ffmpeg.EnableRaisingEvents = true;
  
              ffmpeg.Start();
  
  
  
              var stream = ffmpeg.StandardOutput.BaseStream;
  
              var img = Image.FromStream(stream);
  
              //ffmpeg.WaitForExit();
  
  
  
              return img;
  
          }
  
      }   

  The problem is that I want to grab real-time (latest) images when I request.

  If I run FFmpegHandler.init(), it will take 2 seconds to give me delayed image output.

  I have tried removing argument -vframes 1, then it will hang after image = Image.FromStream(stream) ;.

  When I check the ffmpeg output directly, it looks like ffmpeg is keep building the stream

  frame=    6 fps=0.0 q=2.2 size=      25kB time=00:00:00.24 bitrate= 861.9kbits/s dup=4 drop=0 speed=0.435x    
  
  frame=   65 fps= 60 q=24.8 size=     140kB time=00:00:02.60 bitrate= 440.9kbits/s dup=4 drop=0 speed=2.41x    
  
  frame=   77 fps= 49 q=24.8 size=     161kB time=00:00:03.08 bitrate= 428.0kbits/s dup=4 drop=0 speed=1.95x    
  
  frame=   89 fps= 43 q=24.8 size=     182kB time=00:00:03.56 bitrate= 418.6kbits/s dup=4 drop=0 speed= 1.7x    
  
  frame=  102 fps= 39 q=24.8 size=     205kB time=00:00:04.08 bitrate= 410.7kbits/s dup=4 drop=0 speed=1.57x    
  
  frame=  116 fps= 37 q=24.8 size=     229kB time=00:00:04.64 bitrate= 404.2kbits/s dup=4 drop=0 speed=1.49x    
  
  frame=  128 fps= 35 q=24.8 size=     250kB time=00:00:05.12 bitrate= 399.8kbits/s dup=4 drop=0 speed=1.41x    
  
  frame=  142 fps= 34 q=24.8 size=     274kB time=00:00:05.68 bitrate= 395.7kbits/s dup=4 drop=0 speed=1.36x    
  
  frame=  156 fps= 33 q=24.8 size=     299kB time=00:00:06.24 bitrate= 392.3kbits/s dup=4 drop=0 speed=1.32x    
  
  frame=  169 fps= 32 q=24.8 size=     322kB time=00:00:06.76 bitrate= 389.7kbits/s dup=4 drop=0 speed=1.29x    
  
  frame=  182 fps= 32 q=24.8 size=     344kB time=00:00:07.28 bitrate= 387.4kbits/s dup=4 drop=0 speed=1.26x    
  
  frame=  195 fps= 31 q=24.8 size=     367kB time=00:00:07.80 bitrate= 385.5kbits/s dup=4 drop=0 speed=1.24x    
  
  frame=  208 fps= 31 q=24.8 size=     390kB time=00:00:08.32 bitrate= 383.8kbits/s dup=4 drop=0 speed=1.22x    
  
  frame=  221 fps= 30 q=24.8 size=     413kB time=00:00:08.84 bitrate= 382.3kbits/s dup=4 drop=0 speed=1.21x   

  How can I grab the latest frames out of this live-stream image ? (OR is there a thread-safe way to clean the stream and only get the latest frame when I request ?)

• Python gets stuck at pipe.stdin.write(image.tostring())

  10 mars 2020, par Vandana Rajan

  I am reading each frame of video and adding time stamp to it as given below.

  command = ['ffmpeg',
  
              '-y', # (optional) overwrite output file if it exists
  
              '-f', 'rawvideo', #Input is raw video
  
              '-pix_fmt', 'bgr24', #Raw video format
  
              '-s', str(int(width)) + 'x' + str(int(height)), # size of one frame
  
              '-i', '-', # The input comes from a pipe
  
              '-an', # Tells FFMPEG not to expect any audio
  
              '-vcodec', 'mpeg4',
  
              '-b:v', '10M', #Sets a maximum bit rate
  
              Output_name]
  
      #Open the pipe
  
      pipe = sp.Popen(command, stdin=sp.PIPE, stderr=sp.PIPE)
  
  
  
      print('Processing....')
  
      print(' ')
  
      #Reads through each frame, calculates the timestamp, places it on the frame and exports the frame to the output video.
  
      #import pdb
  
      #pdb.set_trace()
  
      while current_frame < total_frames:
  
          success, image = video.read()
  
          if success:
  
              elapsed_time = video.get(cv2.CAP_PROP_POS_MSEC)
  
              current_frame = video.get(cv2.CAP_PROP_POS_FRAMES)
  
              timestamp = initial + dt.timedelta(microseconds = elapsed_time*1000)
  
              cv2.putText(image, 'Date: ' + str(timestamp)[0:10], (50,int(height-150)), cv2.FONT_HERSHEY_COMPLEX_SMALL, 2, (255, 255, 255), 3)
  
              cv2.putText(image, 'Time: ' + str(timestamp)[11:-4], (50,int(height-100)), cv2.FONT_HERSHEY_COMPLEX_SMALL, 2, (255, 255, 255), 3)
  
              pipe.stdin.write(image.tostring())
  
              print('frame number',current_frame)
  
          else:
  
              print('video reader fail')    
  
      video.release()
  
      pipe.stdin.close()
  
      pipe.stderr.close()

  However, after around 18k frames, Python gets stuck at ’pipe.stdin.write(image.tostring())’. It does not produce any error, but simply hangs. How to resolve this issue ?

  Thanks in advance.