Recherche avancée

Sur d’autres sites (10513)

• 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 link error : undefined reference in library sources

  31 janvier 2016, par Arton

  I downloaded the ffmpeg from git, and make the libs by sources. Created main.c as below and put the ffmpeg libs in the same folder as main.c, (my system is ubuntu 15.10, gcc version 5.2.1)

  #include 
  
  void av_register_all(void);
  
  int main() {
  
      printf("abc\n");
  
      av_register_all();
  
      return 0;
  
  }

  After I issued gcc main.c -L. -lavformat -lswscale  -lavcodec -lswscale -lavutil -lavdevice -lavfilter, I got a lot of (nearly 1000) undefined reference errors :

  ...
  
  /home/arton/sources/ffmpeg/libavcodec/vorbisdec.c:868: undefined reference to `atan'
  
  /home/arton/sources/ffmpeg/libavcodec/vorbisdec.c:868: undefined reference to `atan'
  
  /home/arton/sources/ffmpeg/libavcodec/vorbisdec.c:869: undefined reference to `atan'
  
  /home/arton/sources/ffmpeg/libavcodec/vorbisdec.c:869: undefined reference to `atan'
  
  /home/arton/sources/ffmpeg/libavcodec/vorbisdec.c:869: undefined reference to `floor'
  
  ...

  /home/arton/sources is where the ffmpeg sources at, I have no idea why it report the sources path of ffmpeg and why the link fails. Any hint is appreciated. Thanks !

• FFMPEG : Videos converted from FLV to MP4 does not play in iPod but works in iPhone

  22 juin, par Shakti Singh

  I used below command to convert videos from FLV,M4V to MP4.

  


  


  ffmpeg -y -i video_1336406262.flv -vcodec libx264 -vpre slow -vpre
ipod640 -b 250k -bt 50k -acodec libfaac -ac 2 -ar 48000 -ab 64k -s
480x320 video_1336406262.mp4

  


  


  The videos converted from M4V to MP4 are playing very well in both iPhone and iPod but the videos converted from FLV to MP4 does not work in iPod but does in iPhone.

  


  In the video area of HTML5 page iPod even does not show the play symbol.

  


  I am using the same command to convert from both FLV and M4V to MP4.