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• How to fetch both live video frame and timestamp from ffmpeg to python on Windows

  6 mars 2017, par vijiboy

  Searching for an alternative as OpenCV would not provide timestamps for live camera stream (on Windows), which are required in my computer vision algorithm, I found ffmpeg and this excellent article https://zulko.github.io/blog/2013/09/27/read-and-write-video-frames-in-python-using-ffmpeg/
  The solution uses ffmpeg, accessing its standard output (stdout) stream. I extended it to read the standard error (stderr) stream as well.

  Working up the python code on windows, while I received the video frames from ffmpeg stdout, but the stderr freezes after delivering the showinfo videofilter details (timestamp) for first frame.

  I recollected seeing on ffmpeg forum somewhere that the video filters like showinfo are bypassed when redirected. Is this why the following code does not work as expected ?

  Expected : It should write video frames to disk as well as print timestamp details.
  Actual : It writes video files but does not get the timestamp (showinfo) details.

  Here’s the code I tried :

  import subprocess as sp
  
  import numpy
  
  import cv2
  
  
  
  command = [ 'ffmpeg', 
  
              '-i', 'e:\sample.wmv',
  
              '-pix_fmt', 'rgb24',
  
              '-vcodec', 'rawvideo',
  
              '-vf', 'showinfo', # video filter - showinfo will provide frame timestamps
  
              '-an','-sn', #-an, -sn disables audio and sub-title processing respectively
  
              '-f', 'image2pipe', '-'] # we need to output to a pipe
  
  
  
  pipe = sp.Popen(command, stdout = sp.PIPE, stderr = sp.PIPE) # TODO someone on ffmpeg forum said video filters (e.g. showinfo) are bypassed when stdout is redirected to pipes??? 
  
  
  
  for i in range(10):
  
      raw_image = pipe.stdout.read(1280*720*3)
  
      img_info = pipe.stderr.read(244) # 244 characters is the current output of showinfo video filter
  
      print "showinfo output", img_info
  
      image1 =  numpy.fromstring(raw_image, dtype='uint8')
  
      image2 = image1.reshape((720,1280,3))  
  
  
  
      # write video frame to file just to verify
  
      videoFrameName = 'Video_Frame{0}.png'.format(i)
  
      cv2.imwrite(videoFrameName,image2)
  
  
  
      # throw away the data in the pipe's buffer.
  
      pipe.stdout.flush()
  
      pipe.stderr.flush()

  So how to still get the frame timestamps from ffmpeg into python code so that it can be used in my computer vision algorithm...

• How to fetch both live video frame and its timestamp from ffmpeg on Windows

  22 février 2017, par vijiboy

  Searching for an alternative as OpenCV would not provide timestamps for live camera stream (on Windows), which are required in my computer vision algorithm, I found ffmpeg and this excellent article https://zulko.github.io/blog/2013/09/27/read-and-write-video-frames-in-python-using-ffmpeg/
  The solution uses ffmpeg, accessing its standard output (stdout) stream. I extended it to read the standard error (stderr) stream as well.

  Working up the python code on windows, while I received the video frames from ffmpeg stdout, but the stderr freezes after delivering the showinfo videofilter details (timestamp) for first frame.

  I recollected seeing on ffmpeg forum somewhere that the video filters like showinfo are bypassed when redirected. Is this why the following code does not work as expected ?

  Expected : It should write video frames to disk as well as print timestamp details.
  Actual : It writes video files but does not get the timestamp (showinfo) details.

  Here’s the code I tried :

  import subprocess as sp
  
  import numpy
  
  import cv2
  
  
  
  command = [ 'ffmpeg', 
  
              '-i', 'e:\sample.wmv',
  
              '-pix_fmt', 'rgb24',
  
              '-vcodec', 'rawvideo',
  
              '-vf', 'showinfo', # video filter - showinfo will provide frame timestamps
  
              '-an','-sn', #-an, -sn disables audio and sub-title processing respectively
  
              '-f', 'image2pipe', '-'] # we need to output to a pipe
  
  
  
  pipe = sp.Popen(command, stdout = sp.PIPE, stderr = sp.PIPE) # TODO someone on ffmpeg forum said video filters (e.g. showinfo) are bypassed when stdout is redirected to pipes??? 
  
  
  
  for i in range(10):
  
      raw_image = pipe.stdout.read(1280*720*3)
  
      img_info = pipe.stderr.read(244) # 244 characters is the current output of showinfo video filter
  
      print "showinfo output", img_info
  
      image1 =  numpy.fromstring(raw_image, dtype='uint8')
  
      image2 = image1.reshape((720,1280,3))  
  
  
  
      # write video frame to file just to verify
  
      videoFrameName = 'Video_Frame{0}.png'.format(i)
  
      cv2.imwrite(videoFrameName,image2)
  
  
  
      # throw away the data in the pipe's buffer.
  
      pipe.stdout.flush()
  
      pipe.stderr.flush()

  So how to still get the frame timestamps from ffmpeg into python code so that it can be used in my computer vision algorithm...

• Raw Audio from NAudio

  20 février 2017, par Ken

  I want to record raw audio from WASAPI loopback by NAudio and pipe to FFmpeg for streaming via memory stream. As from this document, FFmpeg can get input as Raw However, I got result speed at 8 10x !
  Here is my code :

  waveInput = new WasapiLoopbackCapture();
  
  waveInput.DataAvailable += new EventHandler<waveineventargs>((object sender, WaveInEventArgs e) => 
  
  {
  
      lock (e.Buffer)
  
      {
  
          if (waveInput == null)
  
              return;
  
          try
  
          {
  
              using (System.IO.MemoryStream memoryStream = new System.IO.MemoryStream())
  
              {
  
                  memoryStream.Write(e.Buffer, 0, e.Buffer.Length);
  
                  memoryStream.WriteTo(ffmpeg.StandardInput.BaseStream);
  
              }
  
          }
  
          catch (Exception)
  
          {
  
              throw;
  
          }
  
      }
  
  });
  
  waveInput.StartRecording();
  
  </waveineventargs>

  FFmpeg Arguments :

  ffmpegProcess.StartInfo.Arguments = String.Format("-f s16le -i pipe:0 -y output.wav");

  1. Can someone please explain this situation and give me a solution ?
  2. Should I add Wav header to the Memory Stream then pipe to FFmpeg as Wav format ?

  The Working Solution

  waveInput = new WasapiLoopbackCapture();
  
  waveInput.DataAvailable += new EventHandler<waveineventargs>((object sender, WaveInEventArgs e) => 
  
  {
  
      lock (e.Buffer)
  
      {
  
          if (waveInput == null)
  
              return;
  
          try
  
          {
  
              using (System.IO.MemoryStream memoryStream = new System.IO.MemoryStream())
  
              {
  
                  memoryStream.Write(e.Buffer, 0, e.BytesRecorded);
  
                  memoryStream.WriteTo(ffmpeg.StandardInput.BaseStream);
  
              }
  
          }
  
          catch (Exception)
  
          {
  
              throw;
  
          }
  
      }
  
  });
  
  waveInput.StartRecording();
  
  </waveineventargs>

  FFMpeg Arguments :

  ffmpegProcess.StartInfo.Arguments = string.Format("-f f32le -ac 2 -ar 44.1k -i pipe:0 -c:a copy -y output.wav");