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• Anomalie #4704 : Par sinum tri le nombre par ordre alpha

  26 mars 2021, par Maïeul Rouquette

  AH ! Donc je comprend enfion cette syntaxe absconne ! Pour moi "par sinum" faisait les deux, vu la phrase

  sinum nom_champ permet d’avoir un tri par numéro avec les éléments numérotés avant ...

  il faudrait plutot dire

  sinum nom_champ met les éléments numérotés avant ... il doit être ensuite combiné avec le critère par num

  parce que moi je ne comprenait par pourquoi on disait "par tri par numéro si il y a un numéro, puis par numero".

  après... why not changer le comportement de par num, on peut se l’assumer en 3.3, non ?

  Par contre cedric tu dis

  (et les rares cas où on voudrait que ceux sans numéros soit en premier, on utilisera sinum...

  si on fait cela, cela voudrait dire que tout les squelettes où l’on a sinum mettrait les numéros... à la fin. Ce qui non seulement ne serait pas cohérent avec le nom du critère, mais en plus casserait les choses. Mais je n’ai pas d’idée de bonne syntaxe

• Matplotlib : Live animation works fine but displays a blank plot when being saved

  18 juillet 2017, par Loïc Poncin

  I made a little forest fire animation. My code is at the end of the question.

  Here is some information before I ask my question :

  • No tree : forest[i,j] = 0
  • A tree : forest[i,j] = 1
  • A tree on fire : forest[i,j] = 2

  Basically what happens is that constructforest creates a 2 dimensional array called forest of size n by m with a probability of tree occupancy called p. After that setonfire sets on fire the forest and while the forest can burn spreadfire spread the fire.

  When I run forestfire with the Python prompt or the IPython prompt I get a nice animation but when I go check the video file that I saved I only see a blank plot.

  I did some research, I found many questions about this issue but none of the advice I read was helpful :

  • matplotlib animation produces a blank
  • Matplotlib animation not working in IPython Notebook (blank plot)
  • Animation from matplotlib not working in spyder
  • Spyder Python Animation not working

  Can someone tell me what is going on please ?

  forestfire.py

  from random import random
  
  
  
  import numpy as np
  
  
  
  import matplotlib.pylab as plt
  
  import matplotlib.colors as mcolors
  
  import matplotlib.animation as animation
  
  
  
  
  
  def hazard(p):
  
      r=random()
  
      assert p>=0 and p<=1
  
      return r <= p
  
  
  
  
  
  def constructforest(n,m,p):
  
      forest = np.zeros((n,n))
  
      for i in xrange(n):
  
          for j in xrange(m):
  
              if hazard(p):
  
                  forest[i,j] = 1
  
      return forest
  
  
  
  
  
  def setfire(forest,i,j):
  
      forest[i,j] = 2
  
      return forest
  
  
  
  
  
  def spreadfire(forest):    
  
  
  
      n,m=forest.shape
  
      c = np.copy(forest)
  
  
  
      for i in xrange(n):
  
          for j in xrange(m):
  
  
  
              if c[i,j] == 1:
  
  
  
                  Y, X = xrange(max(0,i-1),min(n,i+2)), xrange(max(0,j-1),min(m,j+2))
  
  
  
                  for y in Y:
  
                      for x in X:
  
  
  
                          if c[y,x] == 2:
  
                              forest[i,j] = 2                        
  
      return forest
  
  
  
  
  
  def canburn(forest):    
  
  
  
      n,m=forest.shape
  
      c = np.copy(forest)
  
  
  
      for i in xrange(n):
  
          for j in xrange(m):
  
  
  
              if c[i,j] == 1:
  
  
  
                  Y, X = xrange(max(0,i-1),min(n,i+2)), xrange(max(0,j-1),min(m,j+2))
  
  
  
                  for y in Y:
  
                      for x in X:
  
  
  
                          if c[y,x] == 2:
  
                              return True                      
  
      return False
  
  
  
  
  
  def forestfire(forest):
  
  
  
      fig, ax = plt.subplots()
  
  
  
      movie = []    
  
  
  
      # Colormap
  
      red, green, blue = [(1,0,0,1)], [(0,1,0,1)], [(0,0,1,1)]   
  
  
  
      colors = np.vstack((blue, green, red))
  
      mycmap = mcolors.LinearSegmentedColormap.from_list('my_colormap', colors)
  
  
  
      # Initialization
  
      k = 0
  
  
  
      forest = spreadfire(forest)
  
  
  
      im = plt.imshow(forest, animated=True, cmap = mycmap, interpolation="none", origin='lower')
  
      movie.append([im])
  
  
  
      # Fire propagation
  
      while canburn(forest):
  
          k += 1
  
          print k
  
  
  
          forest = spreadfire(forest)
  
  
  
          im = plt.imshow(forest, animated=True, cmap = mycmap, interpolation="none", origin='lower')
  
          movie.append([im])
  
  
  
      return animation.ArtistAnimation(fig, movie, blit=True, repeat_delay=100)
  
  
  
  
  
  
  
  ani = forestfire(setfire(constructforest(101,101,0.4),50,50))
  
  
  
  ani.save("forestfire_test.mp4", writer = 'ffmpeg', fps=5, dpi=500)

  EDIT

  As requested by @Y.Luo by @ImportanceOfBeingErnest in the comments I downgraded matplotlib to 2.0.0 and I changed the framerate of the animation but forestfire_test.mp4 still displays a blank plot.

  Here are my settings :
  
  

• FFmpeg generated video length doesn't match expected length [on hold]

  21 juin 2018, par BentCoder

  I am using command below to generate video out of images. The problem is the length out the video generated. It is always 5 seconds less than expected. If I have 4 images, I expect to see 20 seconds of video but I am getting 15 seconds instead. The very last image img-03.jpg just appears at the end of the video as if it is a cover image. Any idea why and solution ?

  Command

  ffmpeg -y -framerate 1/5 -f image2 \
  
  -i img-%2d.jpg \
  
  -c:v libvpx-vp9 \
  
  -r 25 \
  
  -crf 30 -b:v 0 \
  
  video.webm

  Images

  img-00.jpg
  
  img-01.jpg
  
  img-02.jpg
  
  img-03.jpg

  Output

  ffmpeg version 3.2.10-1~deb9u1~bpo8+1 Copyright (c) 2000-2018 the FFmpeg developers
  
    built with gcc 4.9.2 (Debian 4.9.2-10)
  
    configuration: --prefix=/usr --extra-version='1~deb9u1~bpo8+1' --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --disable-libebur128 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      55. 34.101 / 55. 34.101
  
    libavcodec     57. 64.101 / 57. 64.101
  
    libavformat    57. 56.101 / 57. 56.101
  
    libavdevice    57.  1.100 / 57.  1.100
  
    libavfilter     6. 65.100 /  6. 65.100
  
    libavresample   3.  1.  0 /  3.  1.  0
  
    libswscale      4.  2.100 /  4.  2.100
  
    libswresample   2.  3.100 /  2.  3.100
  
    libpostproc    54.  1.100 / 54.  1.100
  
  Input #0, image2, from 'img-%2d.jpg':
  
    Duration: 00:00:20.00, start: 0.000000, bitrate: N/A
  
      Stream #0:0: Video: mjpeg, yuvj444p(pc, bt470bg/unknown/unknown), 854x480 [SAR 1:1 DAR 427:240], 0.20 fps, 0.20 tbr, 0.20 tbn, 0.20 tbc
  
  [swscaler @ 0x55f2af60e800] deprecated pixel format used, make sure you did set range correctly
  
  [libvpx-vp9 @ 0x55f2af6276a0] v1.3.0
  
  Output #0, webm, to 'video.webm':
  
    Metadata:
  
      encoder         : Lavf57.56.101
  
      Stream #0:0: Video: vp9 (libvpx-vp9), yuv420p, 854x480 [SAR 1:1 DAR 427:240], q=-1--1, 25 fps, 1k tbn, 25 tbc
  
      Metadata:
  
        encoder         : Lavc57.64.101 libvpx-vp9
  
      Side data:
  
        cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mjpeg (native) -> vp9 (libvpx-vp9))
  
  Press [q] to stop, [?] for help
  
  Input stream #0:0 frame changed from size:854x480 fmt:yuvj444p to size:854x480 fmt:yuvj420p
  
  [swscaler @ 0x55f2af602b60] deprecated pixel format used, make sure you did set range correctly
  
  frame=    4 fps=0.0 q=0.0 Lsize=     214kB time=00:00:15.00 bitrate= 117.0kbits/s speed=  16x    
  
  video:214kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.234810%