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• Filter useless white frames at the beginning and duplicated frames at the end of captured video

  21 septembre 2020, par gumkins

  I'm capturing HTML animation with use of Puppeteer and MediaRecorder API.

  


  Before starting the capturing I'm waiting for networkidle event (I tried networkidle0-2 but result is identical)

  


  await page.goto(url, { waitUntil: 'networkidle0' })


  


  For some reason, the animation starts to play 2-3 seconds after the capturing starts, and thus, white frames are captures.
Similar, at the end of the video there are identical frames because capturing duration is a bit longer than animation plays.

  


  Thus I want to detect and cut off those repeating white frames at the beginning and repeating non-white frames at the end of the video (mp4/webm).

  


  I tried some solutions, like described here, for instance

  


  ffmpeg -i input.mp4 -vf mpdecimate,setpts=N/FRAME_RATE/TB out.mp4


  


  It does remove duplicates, but the problem is that it cuts off dups in the middle as well.

  


  Thus, if I have a 15 sec animation,it removes all dups at the beginning, all dups at the end and all dups in the middle, and what is left after it is just a several identical frames which are pack into less than 1 sec video.

  


• ffmpeg convert white background to transparent

  7 janvier 2021, par tony

  Hello i took a picture of a framed sheet with my camera and i'm trying to convert the white background to transparent without using the colorkey filter. It is meant to be for a video using a number of frames overlayed to a static background but i started with only one png to see if it works.

  


  So i started making 1 palette with only 2 colors with -f lavfi (black and white) and 1 palette to add the transparency

  


  ffmpeg -i blackwhite.png -filter_complex "[0:v]split[a][b];[a]palettegen=max_colors=4[out1];\
                            [b]palettegen=max_colors=4:reserve_transparent=on:\
                            transparency_color=#FFFFFF[out2]" \
    -c:v png \
    -map [out1] paletteNormal.png \
    -map [out2] paletteTransparent.png 


  


  then i mapped the png that i want to convert to the first palette to make uniform colors and then to the second to add the transparency and i overlayed the result to a background image that should be red

  


  ffmpeg -i image.png -i paletteNormal.png -i paletteTransparent.png -i background.png \
     -filter_complex "[0:v][1:v]paletteuse=dither=bayer[a],\
     [a]split[a1][a2]; \
     [a1][2:v]paletteuse=alpha_threshold=128[c];[3:v][c]overlay[d]" \
    -map [a2] -c:v png out.png \
    -map [d] -c:v png out1.png


  


  the png mapped to the first palette comes as it should be, pure black and white
the second comes with no transparency at all and covers the background
i tried different combinations like to make the second palette of 255colors..... nothing

  


  what am i doing wrong ? i know it can be done
i went to this site and i made an alpha channel in 5 seconds with a lot of grief and rage.linkOfPain

  


  p.s for a video from png frames what codec should i use ?

  


• ffmpeg convert white color to alpha

  11 janvier 2021, par tony

  Hello i took a picture with my camera :a drawing of a square frame on a white paper ; i'm trying to convert the white to transparent and keep the black color frame.

  


  So i started making 1 palette with only 2 colors to make the colors uniform and 1 palette to add the transparency

  


  ffmpeg -f lavfi -i "color=color=white:100x100" -f lavfi -i "color=color=black:100x100" -filter_complex "[0][1]hstack" -frames:v 1 blackwhite.png`
ffmpeg -i blackwhite.png -filter_complex "[0]split[a][b];[a]palettegen[pal1];[b]palettegen=reserve_transparent=on:transparency_color=white[pal2]" -map [pal1] palette1.png -map [pal2] palette2.png


  


  then i mapped the image png of the frame to convert the white to transparent and overlayed the result to a red background

  


  ffmpeg -i image.png -i palette1.png -i palette2.png -i background.png -filter_complex "[0:v][1:v]paletteuse=dither=bayer[a],[a]split[a1][a2];[a1][2:v]paletteuse=alpha_threshold=128[c];[3:v][c]overlay[d]" -map [a2] -c:v png out.png -map [d] -c:v png out1.png


  


  the png mapped to the first palette (as a test) comes as it should be, pure black and white,the second comes with no transparency at all and covers the background
what am i doing wrong ?