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• Making animations by matplotlib and saving the video files

  20 janvier 2016, par Richard.L

  I have been studying the 1D wave equations and making the animation of the equation. But there are some problems when using the anim.save of animation to save the video file. I have already installed ffmpeg on my computer (a Windows machine) and set the environment variables. But it keeps telling me this :

  UserWarning: MovieWriter ffmpeg unavailable
  
  ...
  
  RuntimeError: Error creating movie, return code: 4 Try running with --verbose-debug

  

  Here is my code :

  from numpy import zeros,linspace,sin,pi
  
  import matplotlib.pyplot as mpl
  
  from matplotlib import animation
  
  mpl.rcParams['animation.ffmpeg_path'] = 'C:\\ffmpeg\\bin\\ffmpeg.exe'
  
  
  
  def I(x):
  
      return sin(2*x*pi/L)
  
  
  
  def f(x,t):
  
      return sin(0.5*x*t)
  
  
  
  def solver0(I,f,c,L,n,dt,t):
  
      # f is a function of x and t, I is a function of x
  
      x = linspace(0,L,n+1)
  
      dx = L/float(n)
  
      if dt <= 0:
  
          dt = dx/float(c)
  
      C2 = (c*dt/dx)**2
  
      dt2 = dt*dt
  
      up = zeros(n+1)
  
      u = up.copy()
  
      um = up.copy()
  
      for i in range(0,n):
  
          u[i] = I(x[i])
  
      for i in range(1,n-1):
  
          um[i] = u[i]+0.5*C2*(u[i-1] - 2*u[i] + u[i+1]) + dt2*f(x[i],t)
  
      um[0] = 0
  
      um[n] = 0    
  
      while t <= tstop:
  
          t_old = t
  
          t += dt
  
          #update all inner points:
  
          for i in range(1,n-1):
  
              up[i] = -um[i] + 2*u[i] + C2*(u[i-1] - 2*u[i] + u[i+1]) + dt2*f(x[i],t_old)    
  
          #insert boundary conditions:
  
          up[0] = 0
  
          up[n] = 0
  
          #update data structures for next step
  
          um = u.copy()
  
          u = up.copy()   
  
      return u
  
  
  
  c = 1.0 
  
  L = 10
  
  n = 100
  
  dt = 0
  
  tstop = 40
  
  
  
  fig = mpl.figure()
  
  ax = mpl.axes(xlim=(0,10),ylim=(-1.0,1.0))
  
  line, = ax.plot([],[],lw=2)
  
  
  
  def init():
  
      line.set_data([],[])
  
      return line,
  
  
  
  def animate(t):
  
      x = linspace(0,L,n+1)
  
      y = solver0(I, f, c, L, n, dt, t)
  
      line.set_data(x,y)
  
      return line,
  
  
  
  anim = animation.FuncAnimation(fig, animate, init_func=init,
  
                                 frames=200, interval=20, blit=True)
  
  
  
  anim.save('seawave_1d_ani.mp4',writer='ffmpeg',fps=30)
  
  mpl.show()

  I believe the problem is in the part of the animation instead of the three functions above. Please help me find what mistake I have made.

• ffmpeg freezes when making a video of 2-3 MB from captured images

  17 juillet 2019, par as04

  I am using the following command in my python script to make a video from a set of images :

  os.system("ffmpeg -framerate 4 -i {0}/img%03d.jpg -c:v libx264 -profile:v high -r 10 -pix_fmt yuv420p {1}/{2}.mp4".format(dir_name, dir_name, name))

  It works fine when creating videos in KB. But ffmpeg freezes for videos of few MB and my raspberry restarts too.
  Also am not very fluent in this tool, so do not understand the parameters well. Please help me with it.

• Overlay on full video length when making video from images sequence using ffmpeg

  30 octobre 2019, par Atta

  I am facing a issue when I overlay watermark image on video (I am making video from images sequence).The issue is that the overlay image only append on first image and ignoring all other images in video. I want to overlay this image on whole video. Possibly I am wrongly applying -filter_graph to input stream. I am executing below mentioned script. I searched online but did not find any relevant answer.

  ffmpeg -r 1/5 -i img%2d.jpeg -i watermark.png -i music.mp3 -filter_complex "[0:v][1:v] overlay=x=10:y=10" video.mp4