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• Trying to capture display output for real-time analysis with OpenCV ; I need help with interfacing with the OS for input

  26 juillet 2024, par mirari

  I want to apply operations from the OpenCV computer vision library, in real time, to video captured from my computer display.
The idea in this particular case is to detect interesting features during gameplay in a popular game and provide the user with an enhanced experience ; but I could think of several other scenarios where one would want to have live access to this data as well. 
At any rate, for the development phase it might be acceptable using canned video, but for the final application performance and responsiveness are obviously critical.

  



  I am trying to do this on Ubuntu 10.10 as of now, and would prefer to use a UNIX-like system, but any options are of interest.
My C skills are very limited, so whenever talking to OpenCV through Python is possible, I try to use that instead.
Please note that I am trying to capture NOT from a camera device, but from a live stream of display output ; and I'm at a loss as to how to take the input. As far as I can tell, CaptureFromCAM works only for camera devices, and it seems to me that the requirement for real-time performance in the end result makes storage in file and reading back through CaptureFromFile a bad option.

  



  The most promising route I have found so far seems to be using ffmpeg with the x11grab option to capture from an X11 display ;
(e.g. the command
ffmpeg -f x11grab -sameq -r 25 -s wxga -i :0.0 out.mpg
captures 1366x768 of display 0 to 'out.mpg').
I imagine it should be possible to treat the output stream from ffmpeg as a file to be read by OpenCV (presumably by using the CaptureFromFile function) maybe by using pipes ; but this is all on a much higher level than I have ever dealt with before and I could really use some directions. 
Do you think this approach is feasible ? And more importantly can you think of a better one ? How would you do it ?

  


• Bump major of libavfilter for reference counted buffer API changes.

  14 décembre 2013, par Reinhard Tartler

  Bump major of libavfilter for reference counted buffer API changes.
  Applications that have been linked against an older release of Libav and pick up
  
  updated libraries experience segmentation faults because they pick up the new
  
  libavfilter, which assumes AVFrames have been allocated by libavutil and thus
  
  contain new reference-counting related fields. This will break for AVFrames that
  
  have been allocated by old libavcodec.
  All scheduled API changes are deferred to the next bump.
  

  • [DBH] doc/APIchanges
  • [DBH] libavfilter/version.h

• How to build ffmpeg executable binary for Android ?

  22 février 2016, par Én Xinh Lung Linh

  I’m struggling how to build an executable binary of ffmpeg for Android command.
  I am very new to ffmpeg which I need to extract audio from video files such as mp4.

  I followed a tutorial here to build ffmpeg binary : http://www.roman10.net/how-to-build-ffmpeg-for-android/

  I dont need *.so file to use in NDK but only an executable binary.

  I tried to enable : --enable-ffmpeg in shell script build. It yielded a ffmpeg file too. Especially, the file size is small with around 2M. However, I am unable to use it in android execution as following :

  p = Runtime.getRuntime().exec("/data/data/example/ffmpeg -i /sdcard/test.mp4  -vn -acodec copy /sdcard/test.aac");

  The above executed very quickly and of course it didn’t give any result.

  I continued searching and found an example here : https://github.com/guardianproject/android-ffmpeg-java

  The ffmpeg binary in the project is nice, I can run some command with desired output. However, some conversions to mp3 format gets failed because probably it lacked libmp3lame when building. Specially, ffmpeg is heavier than mine quite much, it is about 15M. I don’t know how they build the binayr.

  I’m looking for is a proper guide which I can build with arbitrary options such as libmp3lame, libshine. I get stuck at m4a to mp3 conversion.

  Everybody who has experience in ffmpeg, please guide me. Thank you !