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• Use ffmpeg to produce movie with hevc codec and alpha playable in QuickTime

  6 janvier 2021, par 220284

  I want to produce a movie from a sequence of PNG images using ffmpeg. The resulting movie should be QuickTime compatible and is supposed to use the hevc codec with an alpha channel. Can this be done using ffmpeg ? I tried

  


  ffmpeg -framerate 60 -i %d.png -c:v libx265 -pix_fmt yuv420p -x265-params lossless=1 -tag:v hvc1 out.mov


  


  but the resulting movie has no alpha channel.

  


• Révision 23381 : Intégration du plugin Menu Prive Alpha, suite.

  5 février 2017, par marcimat@rezo.net

  On complète les boutons des menus par l’information "favori" (booleen). Si une entrée de menu favorite est cochée dans les préférences,
  cette valeur vaudra `true` dans le bouton, `false` sinon.

  On ajoute 2 fonctions pour trier les sous-menus de navigation afin d’avoir soit un tri "par favori, titre alpha" ou simplement "par titre alpha".
  On utilise ces fonctions dans les squelettes qui affichent les menus. Dans le bandeau, on met tous les favoris en tête de menu.

• OpenCV Alpha Channel support

  14 février 2014, par adriagil

  I've tried many different solutions but I'm stuck at this point.

  I have a sequence of .png files with alpha channel.
  If I pick one of the files for splitting the channels I got the expected result in an array[4] having the alpha channel

  Mat check = imread("1.png");

  printf("channels = %d", check.channels()); //got 'channels = 4'

  Then I expected to get the same results for a movie file.

  With FFMPEG I've just converted the .png sequence to a .mov file with "qtrle" codec that I'm sure that support alpha channel.

  ffmpeg -pix_fmt argb -i sequence_%d.png -vcodec qtrle output.mov

  Then the I process the video file frames with OpenCV

  Mat frame;
  
  VideoCapture cap ("output.mov");
  
  if (cap.grab())
  
      cap.retrieve(frame);
  
  printf("channels = %d", frame.channels()); // got 'channels = 3'

  I've checked the ffmpeg generated output and seems to be encoded right and have the alpha channel stored.

  Does OpenCV does not support Alpha Channel in movie files ?
  If so, anyone knows an alternative to do it with C++ or other libraries ?
  Can this be done with DirectX in some way (only using OpenCV for reading video) ?

  In the official docs I've found that cv::VideocCapture.retrieve() has a second argument for the 'channel' but I've tried to do the following with the same results (no alpha channel) :

  cap.retrieve(frame, 4);
  
  cap.retrieve(frame, -1);

  As far as cv::VideoCapture supports loading image sequences I've tried to load the PNG sequence but I got the following warning so I could not play the movie file :

  VideoCapture cap("sequence_%d.png");
  
  warning: Could not find codec parameters (../../modules/highgui/src/cap_ffmpeg_impl.hpp)

  Why I got that result if I can read the same PNG with imread("") ?

  Also I've tried to encode the .png sequence again with ffmpeg :

  ffmpeg -pix_fmt rgba -i sequence_%d.png -vcodec png output.mov

  But got exactly the same warning as before.

  Any suggestion would be much appreciated !

  Note : I'm using OpenCV 2.4.2 right now...maybe updating to 2.4.8 may solve the problem ?