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• UDP : dont use thread_t as truth value.

  14 mai 2011, par Michael Niedermayer

  UDP : dont use thread_t as truth value.

• `sage -pip install —user ffmpeg` did not make the "`OSError : Error : ffmpeg does not appear to be installed.`" message go away

  2 septembre 2019, par SomeoneElse

  I am running a Docker instance of Cocalc on a Ubuntu 16 server. Everything seems to be working but I am trying to debug why sage -pip install --user ffmpeg did not make the "OSError: Error: ffmpeg does not appear to be installed." message go away, even though it said it had been installed. Here is the full message.

  Error in lines 9-9
  
  Traceback (most recent call last):
  
    File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_server.py", line 1188, in execute
  
      flags=compile_flags) in namespace, locals
  
    File "", line 1, in <module>
  
    File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_salvus.py", line 2944, in show
  
      s = show0(objs, combine_all=True)
  
    File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_salvus.py", line 2903, in show0
  
      b = show0(a)
  
    File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_salvus.py", line 2868, in show0
  
      show_animation(obj, **kwds)
  
    File "/usr/local/sage/local/lib/python2.7/site-packages/smc_sagews/sage_salvus.py", line 2642, in show_animation
  
      obj.ffmpeg(t, delay=delay, **kwds)
  
    File "/usr/local/sage/local/lib/python2.7/site-packages/sage/plot/animate.py", line 885, in ffmpeg
  
      raise OSError(msg)
  
  OSError: Error: ffmpeg does not appear to be installed. Saving an animation to
  
  a movie file in any format other than GIF requires this software, so
  
  please install it and try again.
  
  </module>

  For reference, here is the code that gives the error :

  n = var("n")
  
  frames = []
  
  xr = (x, 0, 1)
  
  for k in srange(1, 50):
  
      g = plot((sum((-1)^(n-1)*sin(n*x)/n,n,1,k)), xr, color="blue", legend_label='k = %d' % k)
  
      g += plot(x/2, xr, color="green", legend_label="x/2")
  
      frames.append(g)
  
  
  
  a = animate(frames, ymin=0.0, ymax=1.0, legend_loc=(0.2,0.8))
  
  a.show()

• Completely remove high frequencies from wav file with ffmpeg

  21 septembre 2021, par Melvin Bender

  For my speech recognition project, I'd like to completely cut off frequencies above 5000Hz on my wav files using ffmpeg.
I understand there is a lowpass filter for reducing frequencies above a certain value :

  


  ffmpeg -i original.wav -af "lowpass=f=5000" lowpass.wav


  


  However when I check the spectogram, it seems like frequencies above 5000 have been reduced, not completely cut off

  


  Voice sample with 5000Hz filter

  


  How can I completely cut off frequencies with ffmpeg ? Any other software is also fine.