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• Direct Show Video capture performance

  23 mai 2019, par Barry Andrews

  I originally started out looking for an example of how I can use FFMPEG in c++ builder to create an application to record from usb capture device and playback video because of apparrent poor performance

  I tried Mitov components, Datastead, FFMPEGVCL and winsoft camera which use directshow but their capture performance seemed poor.

  I need to capture 1920x1080 at up to 60fps into a compressed format and play this back later at both normal speed and slow speed.

  What I found was that DirectShow itself has a number of limitations which can be improved by adding things like FFMPEG, but ultimately PC hardware, in particular the HDD and processor limit capture capability.

  1920x1080 60fps is basically the upper end for DirectShow so you need to have best performing hardware in order to achieve this sort of performance @Spektre kindly gave me examples of DirectShow using the API direct which were good for comparison with the purchased components.

  Using this and comparing to the components I found that MITOV has a major issue with regards the larger video sizes and frame rates. Using this 1920x108 30fps and 60fps can be previewed but they have a massive delay between video feed and preview (5 or 6 seconds). The other components performed similar to the API direct method with only minor variations in performance. None were able to capture and record 1920x108 60fps with any sort of compression filter without large frame drops and very jerky preview.

• libavdevice/gdigrab : fix ffmpeg -devices doesn't show gdigrab

  17 mai 2019, par Jun Zhao

  libavdevice/gdigrab : fix ffmpeg -devices doesn't show gdigrab
  missed the category AV_CLASS_CATEGORY_DEVICE_VIDEO_INPUT lead to
  
  ffmpeg -devices doesn't show gdigrab as a input device
  FIx #7848
  Found-by : dangibson
  
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Jun Zhao <barryjzhao@tencent.com>
  

  • [DH] libavdevice/gdigrab.c

• How can I get my saved mp4 to exactly match the output of plot.show() ?

  10 mai 2019, par Jimmy

  When I try to save the results of an animation to mp4 using ffmpeg, I am getting a jumbled mess.

  plt.show() shows exactly what I want it to show in the animation. However, when I save it using ffmpeg, the result is very different from what plt.show() returns. I have tried various arguments for fps etc. but nothing has helped.

  %matplotlib
  
  import pandas as pd
  
  import matplotlib as mpl ## uncomment this if you are running this on a Mac
  
  #mpl.use('TkAgg')         ## and want to use blit=True
  
  import matplotlib.pyplot as plt 
  
  import matplotlib.animation as animation 
  
  import numpy as np 
  
  import csv
  
  
  
  people = ('','Jim', 'Dan')
  
  plt.rcdefaults()
  
  fig, ax = plt.subplots()
  
  y_pos = np.arange(len(people))
  
  
  
  ax.set_xlim(0,10)
  
  ax.set_yticks(y_pos)
  
  ax.set_yticklabels(people)
  
  ax.invert_yaxis() 
  
  ax.set_xlabel('Skill')
  
  titleList=['Basketball','Hockey','Baseball']
  
  df=[[0,5,7],[0,4,9],[0,2,6]]
  
  def animate(i):
  
     # Example data
  
      while i<3:
  
          ax.set_yticks(y_pos)
  
          ax.set_yticklabels(people)
  
          ax.set_xlabel(titleList[i])
  
          performance=df[i]
  
  
  
          title = ax.text(0.5,0.95,str(titleList[i]), bbox={'facecolor':'w', 'alpha':0.5, 'pad':5},transform=ax.transAxes, ha="center")
  
  
  
          rects = ax.barh(y_pos, performance, align='center',
  
                  color='blue', ecolor='None')
  
          return [rect for rect in rects] + [title]
  
  
  
  
  
  ani = animation.FuncAnimation(fig,animate, frames=3, blit=True
  
                              ,interval=2000,repeat=False)
  
  
  
  plt.rcParams['animation.ffmpeg_path'] = 'C:\\ffmpeg\\bin\\ffmpeg.exe'
  
  Writer = animation.writers['ffmpeg']
  
  ani.save('test.mp4')
  
  plt.show() 

  The result is a very fast video where all the data gets written over (similar to the plt.show() results when blit=False).