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• How to get webam frames one by one but also compressed ?

  29 mars, par Vorac

  I need to grab frames from the webcam of a laptop, transmit them one by one and the receiving side stitch them into a video. I picked ffmpeg-python as wrapper of choice and the example from the docs works right away :

  


  #!/usr/bin/env python

# In this file: reading frames one by one from the webcam.


import ffmpeg

width = 640
height = 480


reader = (
    ffmpeg
    .input('/dev/video0', s='{}x{}'.format(width, height))
    .output('pipe:', format='rawvideo', pix_fmt='yuv420p')
    .run_async(pipe_stdout=True)
)

# This is here only to test the reader.
writer = (
    ffmpeg
    .input('pipe:', format='rawvideo', pix_fmt='yuv420p', s='{}x{}'.format(width, height))
    .output('/tmp/test.mp4', format='h264', pix_fmt='yuv420p')
    .overwrite_output()
    .run_async(pipe_stdin=True)
)


while True:
    chunk = reader.stdout.read(width * height * 1.5)  # yuv
    print(len(chunk))
    writer.stdin.write(chunk)


  


  Now for the compression part.

  


  My reading of the docs is that the input to the reader perhaps needs be rawvideo but nothing else does. I tried replacing rawvideo with h264 in my code but that resulted in empty frames. I'm considering a third invocation looking like this but is that really the correct approach ?

  


  encoder = (                                                                     
    ffmpeg                                                                      
    .input('pipe:', format='rawvideo', pix_fmt='yuv420p', s='{}x{}'.format(width, height))
    .output('pipe:', format='h264', pix_fmt='yuv420p')                          
    .run_async(pipe_stdin=True, pipe_stdout=True)                               


  


• perspective correction example

  10 juillet 2022, par alessandro

  I have some videos taken of a display, with the camera not perfectly oriented, so that the result shows a strong trapezoidal effect.
I know that there is a perspective filter in ffmpeg https://ffmpeg.org/ffmpeg-filters.html#perspective, but I'm too dumb to understand how it works from the docs - and I cannot find a single example.

  



  Somebody can show me how it works ?

  


• Speeding up videocomposing in pymovie

  10 février 2024, par rawlung

  I'm trying to resize videos similarly to what this api provides
https://creatomate.com/docs/json/quick-start/blur-video-background
I accomplished the result more or less but the problem is it takes ages to render out.
I'm a total beginner when it comes to video processing and for the life of me i can't figure out how to speed it up. When the rendering is running python only uses CPU at about 20% utilization.

  


  from moviepy.editor import VideoFileClip, concatenate_videoclips,CompositeVideoClipimport datetimefrom skimage.filters import gaussian

def _blur(image):
  return gaussian(image.astype(float), sigma=25,preserve_range=True,channel_axis=-1)

def blurVideos(filenames):
  clips = [VideoFileClip(c) for c in filenames]
  overlay_clips = [VideoFileClip((c), has_mask=True) for c in filenames]
  overlay = concatenate_videoclips(overlay_clips,"chain")
  output = concatenate_videoclips(clips, method="chain")
  print("Bluring video")
  blured_output = output.fl_image( _blur )
  print("Done")
  print("Resizing video")
  resized_output = blured_output.resize((1920,1080))
  print("Done")
  composited_output = CompositeVideoClip([resized_output.without_audio(),overlay.set_position("center","center")])
  composited_output.write_videofile(f"output/out_{datetime.datetime.today().strftime('%Y-%m-%d')}.mp4",fps=20,threads=16,codec="h264_nvenc",preset="fast")


  


  I've tried to use GPU accelerated codecs like h264_nvenc, I've tried to modify ffmpeg arguments under the hood of moviepy to use cuda also no succses
What can i do to speed this up ?