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• Starting and stopping a system command in C++ based on whether the main program is running

  3 juillet 2018, par zach

  I’m writing a program and I want to use ffmpeg’s x11grab to record the users actions on screen while they interact with the program. I am able to set up the system call to ffmpeg, but I’m not sure how I get it to stop once the program has finished running ?

  Ideally, I would like for the user to hit start (which begins the recording), interact with the main part of the program, hit end, and then have a video file of their session placed somewhere.

  Here’s the code I have so far. This just finds the screen resolution, then calls ffmpeg’s x11grab.

  QRect screen = QApplication::desktop()->screen(QApplication::desktop()->primaryScreen())->geometry();
  
  
  
  int width = screen.width();
  
  int height = screen.height();
  
  
  
  std::string resolution = std::to_string(width) + "x" + std::to_string(height);
  
  std::string record_command = "ffmpeg -f x11grab -s  -r 30 -i :0.0 -qscale 0.1 -vcodec huffyuv grab.avi";
  
  //insert screen resolution into bash command
  
  record_command.insert(21, resolution);
  
  std::cout << record_command;
  
  //bash command to record 
  
  system(record_command.c_str());

• vdpau/h264 : request MAIN rather than BASELINE VDPAU profile for CBP

  26 octobre 2014, par Rémi Denis-Courmont

  vdpau/h264 : request MAIN rather than BASELINE VDPAU profile for CBP
  The H.264 Constrained Baseline Profile (CBP) is a subset of both the
  
  Main Profile and the Baseline Profile. In principles, a hardware
  
  decoder that supports either of those can decode CBP content. As it
  
  happens, Main is supported by all VDPAU drivers, and Baseline is not.
  So favor map CBP to MP for now. Hopefully in the future libvdpau will
  
  offer an explicit choice for CBP.
  This fixes bug 757.
  Signed-off-by : Anton Khirnov <anton@khirnov.net>
  

  • [DBH] libavcodec/vdpau_h264.c

• C++/CLI FFmpeg av_read_frame returns a size but no data ?

  26 novembre 2013, par tommed

  I have written some C code to access ffmpeg and wrapped it in a C++/CLI (.NET managed) class. The program fetches a live video stream and extracts frames and converts them to PNG files.

  Unfortunately the images that are saved to disk are always black (opening them in Notepad++ shows that they are full of nulls).

  I am using the assemblies aformat/codec-55.dll and the development headers and libs for compilation from ffmpeg-20131120-git-e502783-win64-dev. The whole project is compiled using Managed C++ (Cpp/cli) .NET 4.0 for 64-bit.

  After some investigation the problem appears to be that av_read_frame fills the AVPacket->size value correctly, but the AVPAcket->data is always null. When the frame is finished (got==1) then the data for the AVFrame is just a matrix of nulls. :(

  Here is the code :
  Example code (sorry, but it didnt paste well into SO)

  I think the problem is at line 34 when the packet is returned like so :
  

  Please, how can I get this to work ? What have I done wrong ?