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• Animation speed adjustment using ffmpeg in Python

  5 novembre 2015, par neither-nor

  I’m been for years using stock ffmpeg script to sequentially snitch together temporal plots in Python. However, I cannot figure out the trivial issue of how to, for instance, slow down the animation speed so that the resultant video file has a longer duration.

  Example :

  import matplotlib.pyplot as plt
  
  import os, sys
  
  
  
  for t in range(100):
  
      plt.cla()
  
      plt.text(0.5, 0.5, 'time %02d'%(t+1))
  
      plt.draw()
  
  
  
      fname = '_tmp%02d.png'%(t+1)
  
      plt.savefig(fname)
  
  
  
  os.system("ffmpeg -i _tmp%02d.png -pix_fmt yuv420p -r 20 -b:v 20M flipbook.mp4")
  
  os.system("rm _tmp*.png")    

  The resulting "flip book" takes 4s and the time stamp increases steadily. However, I tried to make the animation last twice as long by testing the following :

  1. Change 20 after -r to 1 : this still lasts 4s but now the time stamp "leaps" nonlinearly

  2. Change 20M to 1M : no discernible effect

  I can’t find much information about this line of code, either the usage of each flag or how to modify aspects of it (e.g.,speed).

• fftools/ffplay : fix YUV conversion mode

  21 juin 2022, par Niklas Haas

  fftools/ffplay : fix YUV conversion mode
  GL and Metal cache the state at time of texture creation. GLES2 and
  
  Direct3D 11 use the state at time of the render copy call.
  So the only way we can get the correct behavior consistently is by
  
  making sure the state is set for both the upload *and* the draw call.
  
  This probably isn't our bug to fix (upstream should make itself behave
  
  consistently and also document its functions), but as it stands,
  
  `ffplay` is misrendering BT.709 as BT.601 on my stock Linux system, and
  
  that leaves a bad taste in my mouth.
  Signed-off-by : Niklas Haas <git@haasn.dev>
  

  • [DH] fftools/ffplay.c

• Performance Evaluation of RTX 3080 10G in ffmpeg Transcoding

  26 juin 2023, par JoeLin

  My GPU is RTX 3080 10G ,in ffmpeg , command is :

  


  ffmpeg -loglevel level+info
  
-n -hide_banner -hwaccel cuda -hwaccel_device 0 -hwaccel_output_format cuda
  
-i test.mkv
  
-map 0
  
-c:a copy -preset slow -g 50 -bf 2 -rc:v vbr -cq:v 20 -c:v : h264_nvenc -b:v : 3500k -maxrate:v:0 3500k -bufsize:v:0 7000k -map a:0 -var_stream_map "v:0,a:0,name:1080"
  
"/data/joe/speed/1080_test.mp4"
  
-benchmark

  


  My video file is 3.5G and it takes 27 minutes to execute this command. Can you please tell me if this is within a reasonable range ? By checking the logs, I found that the speed is 7.0x. I would like to know how efficient the transcoding capability of RTX 3080 is and if there are any GPUs with a similar price range that offer better transcoding performance. Alternatively, could there be an issue with my command parameters ? Thank you for your help, guys !

  


  I haven't found similar documentation, so I'm unsure if it's due to an issue with my command