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• 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 ?

• The question about ffmpeg drawtext filter [closed]

  5 mai 2024, par B1GGersnow

  I tried to use rockchip(aarch64) hardware acceleration and add a drawtext filter to add watermarks. However, squares appear when multiple Chinese fonts are added.

  


  This is my compilation parameter.

  


  ./configure --prefix=/usr --enable-gpl --enable-version3 --enable-libdrm --enable-rkmpp --enable-rkrga --enable-filter=drawtext --enable-libharfbuzz --enable-libfreetype --enable-libfontconfig --enable-libfreetype --enable-libfribidi


  


  


  1. ffmpeg -hwaccel rkmpp -hwaccel_output_format drm_prime -i 1.mp4 -vf scale_rkrga=w=1920:h=1080,hwdownload,format=nv12,drawtext=text='中文':fontfile=msyh.ttc:fontsize=200 -c:v h264_rkmpp -y -t 10  output.mp4
img1

     


  


  2. ffmpeg -hwaccel rkmpp -hwaccel_output_format drm_prime -i 1.mp4 -vf "scale_rkrga=w=1920:h=1080,hwdownload,format=nv12,drawtext=text='中文字幕测试':fontfile=msyh.ttc:fontsize=200" -c:v h264_rkmpp -y -t 10  output.mp4
img2

     


  


  


  But I try to use apt install ffmpeg to install ffmpeg which is officially maintained by Ubuntu. I got the right result. So I think it's the library, and I'm trying to compile using the official library.

  


  ./configure --prefix=/usr --enable-gpl --enable-version3 --enable-filter=drawtext --enable-libharfbuzz --enable-libfreetype --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libx264


  


  I still get garbled results.

  


  Is this because there is something wrong with my compilation dependent library ?

  


  When I compiled it with the same parameters on wsl, there was no garbled code.

  


• How can I solve the error when installing ffmpeg [closed]

  11 mars 2024, par zhiyang hou

  OS :
uname -r
3.10.0-957.27.2.el7.x86_64

  


  I performed the following steps on CentOS :

  


  1.Installed dependency libraries :

  


  sudo yum install epel-release -y
sudo yum install autoconf automake cmake freetype-devel gcc gcc-c++ git libtool make      mercurial nasm pkgconfig zlib-devel -y


  


  2.Cloned the FFmpeg repository :

  


  git clone https://git.ffmpeg.org/ffmpeg.git


  


  3.Compiled and installed FFmpeg :

  


  cd ffmpeg
./configure --enable-shared
make -j$(nproc)
sudo make install


  


  Then, I encountered the following issue :

  


  (123) [root@b0a30580415d ffmpeg]# make install
INSTALL libavdevice/libavdevice.a
X86ASM  libavcodec/x86/vvc/vvc_mc.o
libavcodec/x86/vvc/vvc_mc.asm:55: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:55: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:55: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:55: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:55: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:55: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:55: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:56: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:56: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:56: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:56: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:56: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:56: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:56: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:57: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:57: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:57: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:57: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:57: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:57: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:57: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:58: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:58: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:58: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:58: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:58: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:58: error: operand 1: expression is not simple or relocatable
libavcodec/x86/vvc/vvc_mc.asm:58: error: operand 1: expression is not simple or relocatable
make: *** [libavcodec/x86/vvc/vvc_mc.o] Error 1


  


  I am trying to find relevant information on the ffmpeg official website, but I don't know how to solve it. I hope to get guidance from someone with strong technical skills. Thank you.