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• avfilter/vf_ciescope : Fix undefined behavior in rgb_to_xy() with black

  5 juin 2021, par Michael Niedermayer

  avfilter/vf_ciescope : Fix undefined behavior in rgb_to_xy() with black
  Fixes : floating point division by 0
  
  Fixes : undefined behavior in handling NaN
  
  Fixes : Ticket 8268
  Signed-off-by : Michael Niedermayer <michael@niedermayer.cc>
  

  • [DH] libavfilter/vf_ciescope.c

• 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.

  


• ffmpeg video encode add artefacts on very dark scenes (near to black)

  10 juin 2021, par Marco999

  I have many videos ripped from blu ray (h.264).

  


  I don't have sufficient space to store all videos and I like to re-encode all video with hevc codec (h.265) and keep similar quality (not exactly the some) but with a good compromise.

  


  I have tried this command :

  


  ffmpeg.exe -hide_banner -hwaccel nvdec -hwaccel_device 0 -vsync 0 -i "title00.mkv" -c:s copy -an  -c copy -c:v:0 hevc_nvenc -profile:v main10 -pix_fmt p010le  -rc-lookahead 32 -spatial-aq 1 -aq-strength 12  -cq 30 -qmin 1 -qmax 30 -b:v:0 10M -maxrate:v:0 20M -gpu 0  title00_nvidia_no_audio.mkv


  


  the quality is excellent and is very close to original, but on the very dark scenes (near to black) there are visible artefacts.

  


  To solve the problem I have tried this changes without get any improvement :

  


  -cq 25 -qmin 1 -qmax 25 

-spatial-aq 1 -aq-strength 4


  


  For some strange reason seem that if I decrease the -cq from 30 to 25 the artefacts are more visible.

  


  I general I'am satasfied about the quality result but before start the encoding I like to understand if there is a way to reduce/remove these artefacts on very dark scenes.

  


  Any tips ?

  


  Thanks !