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• Layer black & white video over background so black pixels are transparent in FFMPEG

  4 février 2018, par Dan Weaver

  I’m trying to blend a video containing black and white animated text over a static background image. I can successfully blend them but no matter what blend mode I use I can’t get the effect I want.

  I’m looking for an effect similar to Photoshop’s ’Add’ blend mode where the color values of each pixel are added together. This results in no change where the top layer (video) has black pixels, effectively making the black background appear transparent.

  This is what I’m trying to achieve :
  

  ffmpeg -i text.mp4 -loop 1 -i image.jpg \
-filter_complex 'blend=all_mode=addition' -t 1 result.mp4

  I tried all the modes of the blend filter but none of them produce this effect. I thought Addition would be the one to work but the resulting video has a pink tint. Maybe there is some mismatch between color channels ?

  How can I get the result I’m looking for ?

• Append black frames to video when audio is longer in ffmpeg

  8 avril 2018, par Edward

  I’m trying to utilize ffmpeg as a video editor and this is mostly due to that the regular video editor dropped more frames than I was comfortable with.

  ffmpeg -i "videoplayback1" -t 00:09:51 -i "audioplayback1" -t 00:09:54.38 -vcodec libx264 -crf 20 -acodec copy "playback1.mp4"

  As you can see, I’m trimming the video shorter than the audio, but what I want is something that is the opposite of the -shortest command switch, to have the file continue for the duration of the audio -t, and adding physical black frames for the remainder of that time.

  As it is now, the video is still clipped as if I was using the -shortest switch. I tried some -vf and filter_complex but either I get errors, or that the audio is still chopped, the video frozen, but the duration is that of the longest -t.

  How would I go about adding black frames for as long as the audio is playing ?

• Suppress black margins on the sides of an animation

  26 avril 2018, par Clinton Winant

  I need to make an animation out of a collection of jpeg images. The image size, as given by display, is 1200x900. I can control the size of the jpg images with convert, but not sure what a good size would be. I use the following ffmpeg call :

  ffmpeg -f image2 -i img%04d.jpg -r 24  sound.avi

  In spite of a long string of warnings like

  Past duration 0.879997 too large

  sound.avi is produced, however the animation includes black right and left margins (see attached screen shot of the first frame)

  

  that I need to suppress. I am under the impression that the 4x3 format of the jpg images is standard ? I view the animation with

  mplayer sound.avi

  The OS is Debian buster

  Further experiments suggest that the black margins disappear if the jpg files have an aspect ratio 16:9. Is that the only AR possible ?

  The output of

  ffmpeg -f image2 -i img%04d.jpg -vf cropdetect -vframes 5 -f null

  requested by @Gyan is

  ffmpeg version 3.4.2-2 Copyright (c) 2000-2018 the FFmpeg developers
  
    built with gcc 7 (Debian 7.3.0-15)
  
    configuration: --prefix=/usr --extra-version=2 --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --enable-gpl --disable-stripping --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librubberband --enable-librsvg --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libopencv --enable-libx264 --enable-shared
  
    libavutil      55. 78.100 / 55. 78.100
  
    libavcodec     57.107.100 / 57.107.100
  
    libavformat    57. 83.100 / 57. 83.100
  
    libavdevice    57. 10.100 / 57. 10.100
  
    libavfilter     6.107.100 /  6.107.100
  
    libavresample   3.  7.  0 /  3.  7.  0
  
    libswscale      4.  8.100 /  4.  8.100
  
    libswresample   2.  9.100 /  2.  9.100
  
    libpostproc    54.  7.100 / 54.  7.100
  
  Trailing options were found on the commandline.
  
  Input #0, image2, from 'img%04d.jpg':
  
    Duration: 00:00:00.40, start: 0.000000, bitrate: N/A
  
      Stream #0:0: Video: mjpeg, yuvj420p(pc, bt470bg/unknown/unknown), 1200x900 [SAR 150:150 DAR 4:3], 25 fps, 25 tbr, 25 tbn, 25 tbc