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• Saving H264 RTP Packets In Useful Form

  14 novembre 2014, par Nick Lima

  I know that it is possible to save RTP h264 streams using Wireshark and VLC. But in order to learn more about video streaming I am trying to do it myself. There are several related questions that make for good reading on this topic :

  How to process raw UDP packets so that they can be decoded by a decoder filter in a directshow source filter

  Problem to Decode H264 video over RTP with ffmpeg (libavcodec)

  How to convert H.264 UDP packets to playable media stream or file (defragmentation)

  With those as background, this is where I am currently :

  • I can receive RTP packets over UTP.
  • I parse packets as discussed in the questions above.
  • I write the packets to a file, separated by \x000001 and add the NAL byte again according to the above guides.
  • At the beginning of the file I put the SPS and PPS which I got from my code’s RTSP conversation with the server (again seperated by the correct bytes).

  I end up with a file of supposedly a lot of NAL frames. I then try to run ffmpeg on the .264 file to create a .mp4. This brings up several errors :

  [h264 @ 0x15257a0] decode_slice_header error

  [h264 @ 0x15257a0] no frame !

  [h264 @ 0x15257a0] non-existing PPS referenced

  [h264 @ 0x15257a0] non-existing PPS 0 referenced

  [buffer @ 0x15e16a0] Invalid pixel format string ’-1’

  I am essentially at a standstill until I can figure out this problem. I have thouroughly read the questions I linked to above, and the stream is definitely viewable because I can connect and watch it via VLC and the incoming packets are definitely H264 RTP packets according to wireshark. If VLC can do it why can’t I ! I would greatly appreciate any insight into my errors and possible a summary of the three linked questions that resolves the disagreements between them.

• Saving Standard Output in memory instead of a file in C#

  19 décembre 2016, par Shawn W

  There is no online tutorial or even a book, for handling Standard Output with C#.

  I want to save standard output in a variable (memory) instead of a file in Shell Execution.

  This for storing thumbnail image from a video file with ffmpeg.

  The below is my code.

  public static void GetThumbnail(string video, string thumbnail, string ffdir)
  
  {
  
      var cmd = " -ss 00:01:00.000 -i " + '"' + video + '"' + " -vcodec rawvideo -vframes 1 -an -f rawvideo -s 320x240 pipe:1 ";
  
  
  
  
  
      var startInfo = new ProcessStartInfo
  
      {
  
          WindowStyle = ProcessWindowStyle.Normal,
  
          FileName = ffdir + "\\ffmpeg.exe ",
  
          Arguments = cmd,
  
          RedirectStandardOutput = true,
  
          UseShellExecute = false
  
      };
  
  
  
      var process = new Process
  
      {
  
          StartInfo = startInfo
  
      };
  
  
  
      process.OutputDataReceived += ProcessOnOutputDataReceived;
  
      process.ErrorDataReceived += ProcessOnOutputDataReceived;
  
  
  
      process.Start();
  
  
  
      process.WaitForExit(1000);
  
  }
  
  
  
  private static void ProcessOnOutputDataReceived(object sender, DataReceivedEventArgs dataReceivedEventArgs)
  
  {
  
      ....
  
  }

  But it does not enter to the event handler function (ProcessOnOutputDataReceived) when GetThumbnail function launched.

  Is there any clue to solve this problem ?

  I referred the question and answer here :
  getting mulitple images from a single stream piped from ffmpeg stdout

  But it does not help. It seems that the code for previous .NET versions.

• Difficulties saving an animation (matplotlib)

  14 avril 2020, par Ben C.

  I have a simple animation that I want to save. I followed the example : https://matplotlib.org/examples/animation/basic_example_writer.html

  



  But I get the following error : RuntimeError : Requested MovieWriter (ffmpeg) not available

  



  I installed ffmpeg and checked via ffmpeg -version that it really is installed and the path correct.

  



  Here is my code :

  



  import numpy as np
import matplotlib.animation as animation
import matplotlib.pyplot as plt

# Set up formatting for the movie files
Writer = animation.writers['ffmpeg']
writer = Writer(fps=15, metadata=dict(artist='Me'), bitrate=1800)

fig, ax = plt.subplots()

x = np.random.uniform(0,1)
y = np.random.uniform(0,1)


scat = ax.scatter(x,y, color= 'blue')
circle = plt.Circle((x,y), radius=0.1, color='blue', fill=False, lw=0.5)
ax.add_patch(circle)

def init():
    scat = ax.scatter(x, y, color = 'blue')
    circle = plt.Circle((x,y), radius=0.1, color='blue', fill=False, lw=0.5)

def animate(i):
    random = np.random.uniform(0,1)
    if random < 0.5:
        scat.set_color('red')
        circle.set_edgecolor('blue')
    else:
        scat.set_color('blue')
        circle.set_edgecolor('red')
    return circle, scat,


ani = animation.FuncAnimation(fig, animate, init_func=init(), interval=1000, blit=True)
ani.save('test.mp4', writer=writer)


  



  None of the proposed solution in RuntimeError : No MovieWriters available in Matplotlib animation worked for me. Any ideas ?

  



  Edit : I am using Windows (10)