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• I get black screen when i record the headless selenium driver with xvfb and ffmpeg [closed]

  28 juillet 2022, par Saran Raj

  xvfb-run —listen-tcp —server-num 44 -s "-ac -screen 0 1920x1080x24" mvn clean test &
  
export DISPLAY=:44
  
ffmpeg -f x11grab -video_size 1920x1080 -i :44 -codec:v libx264 -r 12 video.mp4

  


  This is the bash script i am using to run the selenium test cases(in headless mode) with maven as the build tool in port 44 and capture it.
But when i execute it i only get a black screen. What to do ?

  


• FFmpeg / Avconv video playback problems - black or green tint

  21 octobre 2014, par scottpaterson

  I am using FFmpeg / Avconv to convert a raw video file to a MP4 or AVI. Both FFmpeg and Avconv have the same problem.

  • The output video, both MP4 or AVI, play 100% percent perfect on Linux Mint in the default video player.

  • On Windows in WMP the MP4 plays, but the video is black, and the AVI plays and shows video but it has a green tint. On Windows in Quicktime both formats video is black.

  Here is the command I am using :

   avconv -i /home/scott/Desktop/out.wav -f rawvideo -pix_fmt rgb32 -s:v 540x240 -i 
  
   /home/scott/Desktop/out.raw -c:v libx264 -strict -2 -preset ultrafast -b:v 160k  
  
   /home/scott/Dropbox/code/out.avi

  • I have spent a lot of time messing with the -pix_fmt and trying different pixel format, so far rgb32 returns the best results.

  • I have also tried -sws_flags options such as lanczos+accurate_rnd - but this did not help.

  How can I get this to play the same in all video players ?

  Thanks !

• moviepy black border around png when compositing into an MP4

  27 août 2022, par OneWorld

  compositing a png into an MP4 video creates a black border around the edge.

  


  This is using moviepy 1.0.0

  


  Code below reproduces the MP4 with the attached red text png.

  


  

  


  import numpy as np
import moviepy.editor as mped
def composite_txtpng_on_colour():
    bg_color = mped.ColorClip(size=[400, 300], color=np.array([0, 255, 0]).astype(np.uint8),
                          duration=2).set_position((0, 0))
    text_png_postition = [5, 5]
    text_png = mped.ImageClip("./txtpng.png", duration=3).set_position((text_png_postition))

    canvas_size = bg_color.size
    stacked_clips = mped.CompositeVideoClip([bg_color, text_png], size=canvas_size).set_duration(2)
    stacked_clips.write_videofile('text_with_black_border_video.mp4', fps=24)

composite_txtpng_on_colour()


  


  The result is an MP4 that can be played in VLC player. A screenshot of the black edge can be seen below :-

  


  

  


  Any suggestions to remove the black borders would be much appreciated.

  


  Update : It looks like moviepy does a blit instead of alpha compositing.

  


  def blit(im1, im2, pos=None, mask=None, ismask=False):
    """ Blit an image over another.  Blits ``im1`` on ``im2`` as position ``pos=(x,y)``, using the
    ``mask`` if provided. If ``im1`` and ``im2`` are mask pictures
    (2D float arrays) then ``ismask`` must be ``True``.
    """
    if pos is None:
        pos = [0, 0]

    # xp1,yp1,xp2,yp2 = blit area on im2
    # x1,y1,x2,y2 = area of im1 to blit on im2
    xp, yp = pos
    x1 = max(0, -xp)
    y1 = max(0, -yp)
    h1, w1 = im1.shape[:2]
    h2, w2 = im2.shape[:2]
    xp2 = min(w2, xp + w1)
    yp2 = min(h2, yp + h1)
    x2 = min(w1, w2 - xp)
    y2 = min(h1, h2 - yp)
    xp1 = max(0, xp)
    yp1 = max(0, yp)

    if (xp1 >= xp2) or (yp1 >= yp2):
        return im2

    blitted = im1[y1:y2, x1:x2]

    new_im2 = +im2

    if mask is None:
        new_im2[yp1:yp2, xp1:xp2] = blitted
    else:
        mask = mask[y1:y2, x1:x2]
        if len(im1.shape) == 3:
            mask = np.dstack(3 * [mask])
        blit_region = new_im2[yp1:yp2, xp1:xp2]
        new_im2[yp1:yp2, xp1:xp2] = (1.0 * mask * blitted + (1.0 - mask) * blit_region)
    
    return new_im2.astype('uint8') if (not ismask) else new_im2


  


  and so, Rotem is right.

  


  new_im2[yp1:yp2, xp1:xp2] = (1.0 * mask * blitted + (1.0 - mask) * blit_region)


  


  is

  


  (alpha * img_rgb + (1.0 - alpha) * bg)


  


  and this is how moviepy composites. And this is why we see black at the edges.