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• even though my code is running without an error, it does not generate plot or video. I have xming runing

  23 octobre 2017, par Amin Abbasi

  This is my first code and I am really new to coding. I am trying to create a video or just plot my code.Eeven though my code is running without an error, I can’t get the video or the plot to generate. I have xming running and I have plotted a sample to make sure it not a computer Issue. I have also tried the following on GitHub but no success :
  https://jakevdp.github.io/blog/2013/05/19/a-javascript-viewer-for-matplotlib-animations/

  # -*- coding: utf-8 -*-
  
  import numpy as np
  
  def solver(I, V, f, c, L, dt, cc, T, user_action=None):
  
      """Solve u_tt=c^2*u_xx + f on (0,L)x(0,T]."""
  
      Nt = int(round(T/dt))
  
      t = np.linspace(0, Nt*dt, Nt+1) # Mesh points in time
  
      dx = dt*c/float(cc)
  
      Nx = int(round(L/dx))
  
      x = np.linspace(0, L, Nx+1) # Mesh points in space
  
      C2 = cc**2 # Help variable in the scheme
  
      # Make sure dx and dt are compatible with x and t
  
      dx = x[1] - x[0]
  
      dt = t[1] - t[0]
  
      if f is None or f == 0 :
  
          f = lambda x, t: 0
  
      if V is None or V == 0:
  
          V = lambda x: 0
  
      u       = np.zeros(Nx+1) # Solution array at new time level
  
      u_n     = np.zeros(Nx+1) # Solution at 1 time level back
  
      u_nm1   = np.zeros(Nx+1) # Solution at 2 time levels back
  
      import time; t0 = time.clock() # Measure CPU time
  
      # Load initial condition into u_n
  
      for i in range(0,Nx+1):
  
          u_n[i] = I(x[i])
  
      if user_action is not None:
  
          user_action(u_n, x, t, 0)
  
      # Special formula for first time step
  
      n = 0
  
      for i in range(1, Nx):
  
          u[i] = u_n[i] + dt*V(x[i]) + \
  
              0.5*C2*(u_n[i-1] - 2*u_n[i] + u_n[i+1]) + \
  
              0.5*dt**2*f(x[i], t[n])
  
      u[0] = 0; u[Nx] = 0
  
      if user_action is not None:
  
          user_action(u, x, t, 1)
  
      # Switch variables before next step
  
      u_nm1[:] = u_n; u_n[:] = u
  
      for n in range(1, Nt):
  
          # Update all inner points at time t[n+1]
  
          for i in range(1, Nx):
  
              u[i] = - u_nm1[i] + 2*u_n[i] + \
  
                      C2*(u_n[i-1] - 2*u_n[i] + u_n[i+1]) + \
  
                      dt**2*f(x[i], t[n])
  
          # Insert boundary conditions
  
          u[0] = 0; u[Nx] = 0
  
          if user_action is not None:
  
              if user_action(u, x, t, n+1):
  
                  break
  
          # Switch variables before next step
  
          u_nm1[:] = u_n; u_n[:] = u
  
      cpu_time = time.clock() - t0
  
      return u, x, t,
  
  def test_quadratic():
  
      """Check that u(x,t)=x(L-x)(1+t/2) is exactly reproduced."""
  
      def u_exact(x, t):
  
          return x*(L-x)*(1 + 0.5*t)
  
      def I(x):
  
          return u_exact(x, 0)
  
      def V(x):
  
          return 0.5*u_exact(x, 0)
  
      def f(x, t):
  
          return 2*(1 + 0.5*t)*c**2
  
      L = 2.5
  
      c = 1.5
  
      cc = 0.75
  
      Nx = 6 # Very coarse mesh for this exact test
  
      dt = cc*(L/Nx)/c
  
      T = 18
  
      def assert_no_error(u, x, t, n):
  
          u_e = u_exact(x, t[n])
  
          diff = np.abs(u - u_e).max()
  
          tol = 1E-13
  
          assert diff < tol
  
      solver(I, V, f, c, L, dt, cc, T,
  
              user_action=assert_no_error)
  
  def viz(
  
      I, V, f, c, L, dt, C, T,umin, umax, animate=True, tool='matplotlib'):
  
      """Run solver and visualize u at each time level."""
  
      def plot_u_st(u, x, t, n):
  
          """user_action function for solver."""
  
          plt.plot(x, u, 'r-')
  
  #                 xlabel='x', ylabel='u',
  
  #                 axis=[0, L, umin, umax],
  
  #                 title='t=%f' % t[n], show=True)
  
          # Let the initial condition stay on the screen for 2
  
          # seconds, else insert a pause of 0.2 s between each plot
  
          time.sleep(2) if t[n] == 0 else time.sleep(0.2)
  
          plt.savefig('frame_%04d.png' % n) # for movie making
  
      class PlotMatplotlib:
  
          def __call__(self, u, x, t, n):
  
              """user_action function for solver."""
  
              if n == 0:
  
                  plt.ion()
  
                  self.lines = plt.plot(x, u, 'r-')
  
                  plt.xlabel('x'); plt.ylabel('u')
  
                  plt.axis([0, L, umin, umax])
  
                  plt.legend(['t=%f' % t[n]], loc='lower left')
  
              else:
  
                  self.lines[0].set_ydata(u)
  
                  plt.legend(['t=%f' % t[n]], loc='lower left')
  
                  plt.draw()
  
              time.sleep(2) if t[n] == 0 else time.sleep(0.2)
  
              plt.savefig('tmp_%04d.png' % n) # for movie making
  
      if tool == 'matplotlib':
  
          import matplotlib.pyplot as plt
  
          plot_u = PlotMatplotlib()
  
      elif tool == 'scitools':
  
          import scitools.std as plt # scitools.easyviz interface
  
          plot_u = plot_u_st
  
      import time, glob, os
  
      # Clean up old movie frames
  
      for filename in glob.glob('tmp_*.png'):
  
          os.remove(filename)
  
      # Call solver and do the simulaton
  
      user_action = plot_u if animate else None
  
      u, x, t, cpu = solver_function(
  
          I, V, f, c, L, dt, C, T, user_action)
  
      # Make video files
  
      fps = 4 # frames per second
  
      codec2ext = dict(flv='flv', libx264='mp4', libvpx='webm',
  
                       libtheora='ogg') # video formats
  
      filespec = 'tmp_%04d.png'
  
      movie_program = 'ffmpeg' # or 'avconv'
  
      for codec in codec2ext:
  
          ext = codec2ext[codec]
  
          cmd = '%(movie_program)s -r %(fps)d -i %(filespec)s '\
  
                '-vcodec %(codec)s movie.%(ext)s' % vars()
  
          os.system(cmd)
  
      if tool == 'scitools':
  
          # Make an HTML play for showing the animation in a browser
  
          plt.movie('tmp_*.png', encoder='html', fps=fps,
  
                    output_file='movie.html')
  
      return cpu

• Use lutyuv to calculate u component from y component

  20 août 2019, par user3931835

  In FFMpeg I use as filter

      lutyuv="y=0.000018712*val*val+0.0027334*val+1.3141:u=gammaval(1.09)"

  This works well. Now I want to calculate u value as a function of calculated y, something like u=1.1*previous_calculated_y*val. How can I access previously calculated y value in formula for u ? Or how can I access y information in formula for u ?

  Example : If y value was zero I would like to get for u = 1.3141*val.

  I googled and found nothing.

  lutyuv="y=0.000018712*val*val+0.0027334*val+1.3141:u=gammaval(1.09)"

• Delphi, TBitmap (rgb) to YCbCr colors format

  18 octobre 2019, par Alexander M.

  have a video encoding example from http://www.delphiffmpeg.com - need to convert a set of TBitmaps to YCbCr (YUV), how should we do it ? the example contains dummy colors :

    (* encode 1 second of video *)
  
    idx := 1;
  
    for i := 0 to 25 - 1 do
  
    begin
  
      av_init_packet(@pkt);
  
      pkt.data := nil;    // packet data will be allocated by the encoder
  
      pkt.size := 0;
  
  
  
      //fflush(stdout);
  
      (* prepare a dummy image *)
  
      (* Y *)
  
      for y := 0 to c.height - 1 do
  
        for x := 0 to c.width - 1 do
  
          PByte(@PAnsiChar(frame.data[0])[y * frame.linesize[0] + x])^ := x + y + i * 3;
  
  
  
      (* Cb and Cr *)
  
      for y := 0 to c.height div 2 - 1 do
  
        for x := 0 to c.width div 2 - 1 do
  
        begin
  
          PByte(@PAnsiChar(frame.data[1])[y * frame.linesize[1] + x])^ := 128 + y + i * 2;
  
          PByte(@PAnsiChar(frame.data[2])[y * frame.linesize[2] + x])^ := 64 + x + i * 5;
  
        end;
  
  
  
      frame.pts := i;
  
  
  
      (* encode the image *)
  
      ret := avcodec_encode_video2(c, @pkt, frame, @got_output);
  
      if ret < 0 then
  
      begin
  
        Writeln(ErrOutput, 'Error encoding frame');
  
        ExitCode := 1;
  
        Exit;
  
      end;
  
  
  
      if got_output <> 0 then
  
      begin
  
        Writeln(Format('Write frame %d (size=%d)', [idx, pkt.size]));
  
        FileWrite(f, pkt.data^, pkt.size);
  
        av_packet_unref(@pkt);
  
        Inc(idx);
  
      end;
  
    end;

  But we need to convert bitmaps to YCbCr..instead of filling pixels with dummy image. Here is a full source code :

  (*
  
   * Video encoding example
  
   *)
  
  procedure video_encode_example(const filename: string; codec_id: TAVCodecID);
  
  const
  
    endcode: array[0..3] of Byte = ( 0, 0, 1, $b7 );
  
  var
  
    codec: PAVCodec;
  
    c: PAVCodecContext;
  
    idx, i, ret, x, y, got_output: Integer;
  
    f: THandle;
  
    frame: PAVFrame;
  
    pkt: TAVPacket;
  
  begin
  
    Writeln(Format('Encode video file %s', [filename]));
  
  
  
    (* find the mpeg1 video encoder *)
  
    codec := avcodec_find_encoder(codec_id);
  
    if not Assigned(codec) then
  
    begin
  
      Writeln(ErrOutput, 'Codec not found');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    c := avcodec_alloc_context3(codec);
  
    if not Assigned(c) then
  
    begin
  
      Writeln(ErrOutput, 'Could not allocate video codec context');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    (* put sample parameters *)
  
    c.bit_rate := 400000;
  
    (* resolution must be a multiple of two *)
  
    c.width := 352;
  
    c.height := 288;
  
    (* frames per second *)
  
    c.time_base.num := 1;
  
    c.time_base.den := 25;
  
    (* emit one intra frame every ten frames
  
     * check frame pict_type before passing frame
  
     * to encoder, if frame->pict_type is AV_PICTURE_TYPE_I
  
     * then gop_size is ignored and the output of encoder
  
     * will always be I frame irrespective to gop_size
  
     *)
  
    c.gop_size := 10;
  
    c.max_b_frames := 1;
  
    c.pix_fmt := AV_PIX_FMT_YUV420P;
  
  
  
    if codec_id = AV_CODEC_ID_H264 then
  
      av_opt_set(c.priv_data, 'preset', 'slow', 0);
  
  
  
    (* open it *)
  
    if avcodec_open2(c, codec, nil) < 0 then
  
    begin
  
      Writeln(ErrOutput, 'Could not open codec');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    f := FileCreate(filename);
  
    if f = INVALID_HANDLE_VALUE then
  
    begin
  
      Writeln(ErrOutput, Format('Could not open %s', [filename]));
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    frame := av_frame_alloc();
  
    if not Assigned(frame) then
  
    begin
  
      Writeln(ErrOutput, 'Could not allocate video frame');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
    frame.format := Ord(c.pix_fmt);
  
    frame.width  := c.width;
  
    frame.height := c.height;
  
  
  
    (* the image can be allocated by any means and av_image_alloc() is
  
     * just the most convenient way if av_malloc() is to be used *)
  
    ret := av_image_alloc(@frame.data[0], @frame.linesize[0], c.width, c.height,
  
                         c.pix_fmt, 32);
  
    if ret < 0 then
  
    begin
  
      Writeln(ErrOutput, 'Could not allocate raw picture buffer');
  
      ExitCode := 1;
  
      Exit;
  
    end;
  
  
  
    (* encode 1 second of video *)
  
    idx := 1;
  
    for i := 0 to 25 - 1 do
  
    begin
  
      av_init_packet(@pkt);
  
      pkt.data := nil;    // packet data will be allocated by the encoder
  
      pkt.size := 0;
  
  
  
      //fflush(stdout);
  
      (* prepare a dummy image *)
  
      (* Y *)
  
      for y := 0 to c.height - 1 do
  
        for x := 0 to c.width - 1 do
  
          PByte(@PAnsiChar(frame.data[0])[y * frame.linesize[0] + x])^ := x + y + i * 3;
  
  
  
      (* Cb and Cr *)
  
      for y := 0 to c.height div 2 - 1 do
  
        for x := 0 to c.width div 2 - 1 do
  
        begin
  
          PByte(@PAnsiChar(frame.data[1])[y * frame.linesize[1] + x])^ := 128 + y + i * 2;
  
          PByte(@PAnsiChar(frame.data[2])[y * frame.linesize[2] + x])^ := 64 + x + i * 5;
  
        end;
  
  
  
      frame.pts := i;
  
  
  
      (* encode the image *)
  
      ret := avcodec_encode_video2(c, @pkt, frame, @got_output);
  
      if ret < 0 then
  
      begin
  
        Writeln(ErrOutput, 'Error encoding frame');
  
        ExitCode := 1;
  
        Exit;
  
      end;
  
  
  
      if got_output <> 0 then
  
      begin
  
        Writeln(Format('Write frame %d (size=%d)', [idx, pkt.size]));
  
        FileWrite(f, pkt.data^, pkt.size);
  
        av_packet_unref(@pkt);
  
        Inc(idx);
  
      end;
  
    end;
  
  
  
    (* get the delayed frames *)
  
    repeat
  
      //fflush(stdout);
  
  
  
      ret := avcodec_encode_video2(c, @pkt, nil, @got_output);
  
      if ret < 0 then
  
      begin
  
        Writeln(ErrOutput, 'Error encoding frame');
  
        ExitCode := 1;
  
        Exit;
  
      end;
  
  
  
      if got_output <> 0 then
  
      begin
  
        Writeln(Format('Write frame %d (size=%d)', [idx, pkt.size]));
  
        FileWrite(f, pkt.data^, pkt.size);
  
        av_packet_unref(@pkt);
  
        Inc(idx);
  
      end;
  
    until got_output = 0;
  
  
  
    (* add sequence end code to have a real mpeg file *)
  
    FileWrite(f, endcode[0], SizeOf(endcode));
  
    FileClose(f);
  
  
  
    avcodec_close(c);
  
    av_free(c);
  
    av_freep(@frame.data[0]);
  
    av_frame_free(@frame);
  
    Writeln('');
  
  end;

  yes we know this formula, but what should we do with (* Cb and Cr *) loop that goes up to c.height div 2 - 1 and c.width div 2 - 1 ? all our experiments make correct image geometry but incorrect colors... Here is what we have :

  ( Y )
  
      for y := 0 to c.height - 1 do
  
      begin
  
        Line := image.ScanLine[y];
  
        for x := 0 to c.width - 1 do
  
        begin
  
          Yy := Round(Line[x].R*0.29900 + Line[x].G*0.58700 + Line[x].B*0.11400);
  
          PByte(@PAnsiChar(frame.data[0])[y * frame.linesize[0] + x])^ := Yy;
  
        end;
  
      end;
  
      ( Cb and Cr )
  
      for y := 0 to c.height div 2 - 1 do
  
      begin
  
        Pixels := image.ScanLine[y];
  
        for x := 0 to c.width div 2 - 1 do
  
        begin
  
          Cb := Round(Line[x].R  -0.16874 - Line[x].G  0.33126 + Line[x].B * 0.50000) + 128;
  
          Cr := Round(Line[x].R   0.50000 - Line[x].G  0.41869 - Line[x].B * 0.08131) + 64;
  
          PByte(@PAnsiChar(frame.data[1])[y * frame.linesize[1] + x])^ := Cr;
  
          PByte(@PAnsiChar(frame.data[2])[y * frame.linesize[2] + x])^ := Cb;
  
          //PByte(@PAnsiChar(frame.data[1])[y  frame.linesize[1] + x])^ := 128 + y + i  2;
  
          //PByte(@PAnsiChar(frame.data[2])[y  frame.linesize[2] + x])^ := 64 + x + i  5;
  
        end;
  
      end;

  How this should be fixed ?