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• 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.

  


• 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 ?

• How to use ffmpeg to push my Unity3d process screenshot to nginx-rtmp server ?

  26 mars 2019, par Menghui

  I want to broadcast my Unity process screen.

  What I can think of is to use the Unity screenshot, then pipe png to the ffmpeg process, ffmpeg encodes png into h264 and pushes it to the server.

  How to use ffmpeg and named pipe to encod and push stream ?

  1. About png to h264, is this possible to push ? (But I can’t play server video stream with vlc)

  .\ffmpeg.exe -framerate 24 -i .\screenshot%03d.png -vcodec libx264 -acodec aac -strict -2 -f h264 rtmp://xxx.xxx.xxx.xxx/live

  png -> rtmp image

  2. About ffmpeg and named pipes, it seems to be written, and can not be read.

  # write
  
  .\ffmpeg.exe -i test.mp4 -f h264 pipe:MyPipe

  mp4 -> pipe image

  # read and push stream
  
  .\ffmpeg.exe -re -i pipe:MyPipe -vcodec libx264 -acodec aac -strict -2 -f h264 rtmp://xxx.xxx.xxx.xxx/live

  pipe -> rtmp image

  And ffmpeg official website does not seem to have an introduction about named pipes.

  Thank you for your help !