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• using ffmpeg to resize video with black bars

  23 juillet 2018, par Jens S

  i have a video with resolution 720:576 and i want it to have the ratio 16:9, e.g. 1024:576 with black bars on the sides. don’t know if it matters, but i am working with ffmpeg for windows. After research i tried the solution i found on 2 related questions :

  -i .\video.mp4 -vf scale=1024:576:force_original_aspect_ratio=decrease,pad=1024:576:(ow-iw)/2:(oh-ih)/2,setsar=1 out.mp4

  but i get an output that "ow-iw" was not recognized. Here is the complete output. unfortunatly it is in german(as am i) if u tell me how to change the output language i will provide it in english :

  ow-iw : Die Benennung "ow-iw" wurde nicht als Name eines Cmdlet, einer Funktion, einer Skriptdatei oder eines ausführbaren Programms erkannt. Überprüfen Sie die Schreibweise des
  
  Namens, oder ob der Pfad korrekt ist (sofern enthalten), und wiederholen Sie den Vorgang.
  
  In Zeile:1 Zeichen:119
  
  + ... :576:force_original_aspect_ratio=decrease,pad=1024:576:(ow-iw)/2:(oh- ...
  
  +                                                             ~~~~~
  
      + CategoryInfo          : ObjectNotFound: (ow-iw:String) [], CommandNotFoundException
  
      + FullyQualifiedErrorId : CommandNotFoundException

• ffmpeg puts black frames in the first few seconds of the video

  30 juin 2018, par Joe T. Boka

  I am adding an audio file to a video file, using ffmpy, which is a python wrapper for ffmpeg.

  The input audio file voice.wave and the input video file video.avi are the same length.

  When I use the below code, the output video output.ts contains both audio and video, as expected. The problem : the audio is running fine, but the first few seconds of the output video output.ts is black.

  from ffmpy import FFmpeg
  
  ff = FFmpeg(inputs={'video.avi': None, 'voice.wav': None}, outputs={'output.ts': '-c:v h264 -c:a ac3'})
  
  ff.cmd
  
  'ffmpeg  -i voice.wave -i video.avi -c:v h264 -c:a ac3 output.ts'
  
  ff.run()

• Adding transparency to a video from black and white (and gray) alpha information video images

  3 juillet 2018, par Jan F.

  I’d like to create a video with transparency (and semi transparency) in android. The images of the source video are split into two images, the top one with color information (looks like the normal video image), the bottom one with alpha information (the same shapes but only in black and white and gray, black means transparent).

  This is the solution for iOS :
  https://medium.com/@quentinfasquel/ios-transparent-video-with-coreimage-52cfb2544d54

  What would be the best way to to this in android ?

  Can this be solved with javacv, FFmpegFrameGrabber, FFmpegFrameFilter etc.?

  Or better with OpenGL ES and shaders ?

  Are there any samples ?

  Thanks !