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• Animating a 2D plot (2D brownian motion) not working in Python

  8 avril 2020, par Thamu Mnyulwa

  I am trying to plot a 2D Brownian motion in Python but my plot plots the grid but does not animate the line.

  



  Attempted at performing this plot is below,

  



  !apt install ffmpeg

import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
import matplotlib.animation as animation


np.random.seed(5)


# Set up formatting for the movie files
Writer = animation.writers['ffmpeg']
writer = Writer(fps=15, metadata=dict(artist='Me'), bitrate=1800)


def generateRandomLines(dt, N):
    dX = np.sqrt(dt) * np.random.randn(1, N)
    X = np.cumsum(dX, axis=1)

    dY = np.sqrt(dt) * np.random.randn(1, N)
    Y = np.cumsum(dY, axis=1)

    lineData = np.vstack((X, Y))

    return lineData


# Returns Line2D objects
def updateLines(num, dataLines, lines):
    for u, v in zip(lines, dataLines):
        u.set_data(v[0:2, :num])

    return lines

N = 501 # Number of points
T = 1.0
dt = T/(N-1)


fig, ax = plt.subplots()

data = [generateRandomLines(dt, N)]

ax = plt.axes(xlim=(-2.0, 2.0), ylim=(-2.0, 2.0))

ax.set_xlabel('X(t)')
ax.set_ylabel('Y(t)')
ax.set_title('2D Discretized Brownian Paths')

## Create a list of line2D objects
lines = [ax.plot(dat[0, 0:1], dat[1, 0:1])[0] for dat in data]


## Create the animation object
anim = animation.FuncAnimation(fig, updateLines, N+1, fargs=(data, lines), interval=30, repeat=True, blit=False)

plt.tight_layout()
plt.show()

## Uncomment to save the animation
#anim.save('brownian2d_1path.mp4', writer=writer)


  



  However, instead of performing the plot the program is printing,


  



  How do I animate this plot ? I am new to python so I apologize in advanced if this is an easy question.

  



  I found this question on http://people.bu.edu/andasari/courses/stochasticmodeling/lecture5/stochasticlecture5.html , there is a walkthrough of how this code came to being.

  


• Call ffmpeg in c++ with system() function fails

  2 septembre 2014, par zhen lee

  I write a c++ program which needs to convert some(say:10) mp4 videos to flv videos.
  I use ffmpeg in my program for each video like this :

  system("ffmpeg -i video -filter:v yadif -ar 44100 -sameq -y -f flv temp.flv")

  however,it turns out :only first video will be converted successfully,the others will fail.
  it means :
  when i change the input order of which video to convert and re-execution the program,it behave the same:only the first video(will be different each time as i changed the input video order) will be converted successfully.

  The error message like :

  [h264 @ 0xaee0740] concealing 45 DC, 45 AC, 45 MV errors
  [h264 @ 0xaee0ce0] AVC : nal size 305665
  Last message repeated 1 times
  [h264 @ 0xaee0ce0] no frame !
  [h264 @ 0xaee1280] AVC : nal size 572993
  Last message repeated 1 times
  [h264 @ 0xaee1280] no frame !
  [aac @ 0xad9ccc0] channel element 0.13 is not allocated
  Error while decoding stream #0:1
  [aac @ 0xad9ccc0] channel element 0.13 is not allocated
  Error while decoding stream #0:1
  [aac @ 0xad9ccc0] channel element 0.13 is not allocated
  Error while decoding stream #0:1
  ......
  The most strange thing is :when i run ffmpeg command in bash shell,all video will be converted successfully .

  After google it,I have try these(certainly failed) :

  1. remove -sameq option,the result is same ;

  2. write ffmpeg commod in a shell script ConvertToFlv.sh like :

     /usr/local/bin/ffmpeg -i "$dir/$1" -filter:v yadif -ar 44100 -sameq -y -f flv "$dir/temp.fiv"

     then call this script in program like

     system("ConvertToFlv.sh"+video)

     or

     system("sh ConvertToFlv.sh"+video)

     The result is same.

  The ffmpeg configure is :

    ffmpeg version 0.9.1.git Copyright (c) 2000-2012 the FFmpeg developers
  
    built on Dec 17 2012 16:17:30 with gcc 4.1.2 20080704 (Red Hat 4.1.2-48)
  
    configuration: --enable-gpl --enable-postproc --enable-nonfree --enable-postproc --enable-swscale --enable-avfilter --enable-pthreads --enable-libxvid --enable-libx264 --enable-libmp3lame --enable-libfaac --disable-ffserver --disable-ffplay
  
    libavutil      51. 41.100 / 51. 41.100
  
    libavcodec     54.  4.100 / 54.  4.100
  
    libavformat    54.  1.100 / 54.  1.100
  
    libavdevice    53.  4.100 / 53.  4.100
  
    libavfilter     2. 62.101 /  2. 62.101
  
    libswscale      2.  1.100 /  2.  1.100
  
    libswresample   0.  7.100 /  0.  7.100
  
    libpostproc    52.  0.100 / 52.  0.100

  and my machine envirment is :

  Linux master 2.6.18-194.el5 #1 SMP Fri Apr 2 14:58:14 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux

  I’m irritable now,I hope someone can give me some advice,really appreciate it.

• Layer black & white video over background so black pixels are transparent in FFMPEG

  4 février 2018, par Dan Weaver

  I’m trying to blend a video containing black and white animated text over a static background image. I can successfully blend them but no matter what blend mode I use I can’t get the effect I want.

  I’m looking for an effect similar to Photoshop’s ’Add’ blend mode where the color values of each pixel are added together. This results in no change where the top layer (video) has black pixels, effectively making the black background appear transparent.

  This is what I’m trying to achieve :
  

  ffmpeg -i text.mp4 -loop 1 -i image.jpg \
-filter_complex 'blend=all_mode=addition' -t 1 result.mp4

  I tried all the modes of the blend filter but none of them produce this effect. I thought Addition would be the one to work but the resulting video has a pink tint. Maybe there is some mismatch between color channels ?

  How can I get the result I’m looking for ?