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• How can i crop part of a video while recording from desktop in real time using ffmpeg ? [on hold]

  28 juillet 2017, par daniel llee

  I’m using this line to record from the desktop to a video file :

  ffmpeg -f gdigrab -framerate 24 -i desktop -preset ultrafast -pix_fmt yuv420p out.mp4

  But this will record the whole desktop. Is there any way to record in real time only specific area/part of the desktop ?

  And this is how i’m using the ffmpeg with winforms :

  using System;  
  
  using System.Collections.Generic;  
  
  using System.Linq;  
  
  using System.Text;  
  
  using System.Threading.Tasks;  
  
  using System.IO;  
  
  using System.Diagnostics;  
  
  
  
  namespace Ffmpeg_App  
  
  {  
  
      class Ffmpeg  
  
      {  
  
          Process process;  
  
  
  
          public void Start(string FileName, int Framerate)  
  
          {  
  
              process = new System.Diagnostics.Process();  
  
              process.StartInfo.FileName = @"D:\ffmpegx86\ffmpeg.exe"; // Change the directory where ffmpeg.exe is.  
  
              process.EnableRaisingEvents = false;  
  
              process.StartInfo.WorkingDirectory = @"D:\ffmpegx86"; // The output directory  
  
              process.StartInfo.Arguments = @"-f gdigrab -framerate " + Framerate + " -i desktop -preset ultrafast -                                                                     pix_fmt yuv420p " + FileName;  
  
              process.Start();  
  
              process.StartInfo.UseShellExecute = false;  
  
              process.StartInfo.CreateNoWindow = false;  
  
              Close();  
  
          }  
  
  
  
          public void Close()  
  
          {  
  
              process.Close();  
  
          }  
  
      }  
  
  }  

• Extract images from ffmpeg stream

  30 juillet 2022, par Exitare

  I am trying to setup an application which receives a stream via tcp from a localhost webcam. The stream is generated by ffmpeg like so :

  


  ffmpeg -f avfoundation -framerate 30 -i 0 -target pal-dvd -probesize 42M -pix_fmt uyvy422 -f mpegts -flush_packets 0 tcp://127.0.0.1:9050


  


  My receiving server application code looks like this :

  


  public static void StartServer()
{
   
    bool done = false;

    var listener = new TcpListener(IPAddress.Any, 9050);

    listener.Start();
    
    // Buffer for reading data
    var bytes = new byte[256];
    string data;
    
    while (!done)
    {
        Console.WriteLine("Waiting for connection...");
        TcpClient client = listener.AcceptTcpClient();

        
        data = null;

        // Get a stream object for reading and writing
        NetworkStream stream = client.GetStream();

        int i;
        Console.WriteLine("Connection accepted.");
        // Loop to receive all the data sent by the client.
        while((i = stream.Read(bytes, 0, bytes.Length))!=0)
        {
            // Translate data bytes to a ASCII string.
            Console.WriteLine("Received: {0}", bytes);

            
        }
       
    }

    listener.Stop();
}


  


  ffmpeg is able to connect and send the stream, the c# application is able to receive the stream.

  


  The output by the Console.WriteLine call is like so :

  


  Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]
Received: System.Byte[]


  


  However, I am unsure how to create images from these bytes. In theory I would have to wait until I receive the whole image, as I expect the image to be greater than 256bytes.

  


  In short, I receive the bytes but don't know how to convert them into images.
How do I do this ?

  


  Also I am not sure if this is the best approach. I know that ffmpeg offers the possibility to extract images from videos. But I don't know, whether this is also possible using streams. Is there a solution provided by ffmpeg to extract images from an input stream ? Ideally 10 images per second.

  


• mplayer output 4 audio channels to jack

  14 novembre 2013, par MrCastro

  I am struggling with getting mplayer to reproduce a 4 audio channel wav file.

  I created a 4chn audio file.
  Want mplayer to player, and output it to jack.
  The problem is that i am only able to get in jack 2 mplayer channels.

  if I do :

  mplayer -ao jack -channels 4 test_4chan_2.wav 

  mplayer plays and responds :

  laying test_4chan_2.wav.
  
  libavformat version 54.6.100 (internal)
  
  Audio only file format detected.
  
  Load subtitles in ./
  
  ==========================================================================
  
  Opening audio decoder: [pcm] Uncompressed PCM audio decoder
  
  AUDIO: 44100 Hz, 4 ch, s16le, 2822.4 kbit/100.00% (ratio: 352800->352800)
  
  Selected audio codec: [pcm] afm: pcm (Uncompressed PCM)
  
  ==========================================================================
  
  AO: [jack] 44100Hz 2ch floatle (4 bytes per sample)
  
  Video: no video
  
  Starting playback...

  and jack has only the following outputs :

  system:capture_1
  
  system:capture_2
  
  system:playback_1
  
  system:playback_2
  
  MPlayer [14434]:out_0
  
  MPlayer [14434]:out_1

  So it seems that mplayer recognizes that the input file as 4ch
  but on AO : [jack] only 2ch appear

  if I try the same with ecasound :

  ecasound -f 16,4,44100 -i test_4chan_2.wav -o jack 

  in Jack ecasoud appears with 4 outputs

  system:capture_1
  
  system:capture_2
  
  system:playback_1
  
  system:playback_2
  
  ecasound:out_1
  
  ecasound:out_2
  
  ecasound:out_3
  
  ecasound:out_4

  Do you have any idea of what could I be doing wrong ??
  I am running Debian (Jessy) and mplayer 1.1-4.7

  Thanks a lot