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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 ?

  


• The C compiler "clang.exe" is not able to compile a simple test program

  8 octobre 2020, par M. Bilal Asif

  I am trying to compile shell script that compiles the C project library, but i am stuck at this when it comes to compile the nmake part.

  


  I am using NDK 21 and cmake version is 3.10

  


  I am using shell script using bash same as defined here, i want to compress this library as they showing in the docs running ./android.sh

  


  Please check the link : https://github.com/tanersener/mobile-ffmpeg#52-build-scripts

  


  here is the attached log :

  


  DEBUG: Downloading library source: cpu-features

DEBUG: Checking if cpu-features is already downloaded at /d/Bilals/Projects/GithubProjects/mobile-ffmpeg/src/cpu-features

INFO: cpu-features library already downloaded

INFO: cpu-features already downloaded. Source folder found at /d/Bilals/Projects/GithubProjects/mobile-ffmpeg/src/cpu-features

-- Building for: NMake Makefiles
-- Check for working C compiler: D:/Bilals/PcBackupData/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/windows-x86_64/bin/clang.exe
CMake Error: Generator: execution of make failed. Make command was: "nmake" "/NOLOGO" "cmTC_adf3f\fast"
-- Check for working C compiler: D:/Bilals/PcBackupData/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/windows-x86_64/bin/clang.exe -- broken
CMake Error at D:/Bilals/PcBackupData/sdk/cmake/3.10.2.4988404/share/cmake-3.10/Modules/CMakeTestCCompiler.cmake:52 (message):
  The C compiler

    "D:/Bilals/PcBackupData/sdk/ndk/21.3.6528147/toolchains/llvm/prebuilt/windows-x86_64/bin/clang.exe"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: D:/Bilals/Projects/GithubProjects/mobile-ffmpeg/android/build/cpu-features/arm/CMakeFiles/CMakeTmp
    
    Run Build Command:"nmake" "/NOLOGO" "cmTC_adf3f\fast"
    The system cannot find the file specified
    Generator: execution of make failed. Make command was: "nmake" "/NOLOGO" "cmTC_adf3f\fast"
    

  

  CMake will not be able to correctly generate this project.
Call Stack (most recent call first):
  CMakeLists.txt:9 (project)


-- Configuring incomplete, errors occurred!
See also "D:/Bilals/Projects/GithubProjects/mobile-ffmpeg/android/build/cpu-features/arm/CMakeFiles/CMakeOutput.log".
See also "D:/Bilals/Projects/GithubProjects/mobile-ffmpeg/android/build/cpu-features/arm/CMakeFiles/CMakeError.log".


  


  and here is my environmental variables

  


  

  


• avutil/timecode : fix av_timecode_get_smpte_from_framenum with 50/60 fps

  20 juillet 2020, par Marton Balint

  avutil/timecode : fix av_timecode_get_smpte_from_framenum with 50/60 fps
  SMPTE 12M timecode can only count frames up to 39, because the tens-of-frames
  
  value is stored in 2 bit. In order to resolve this 50/60 fps SMPTE timecode is
  
  using the field bit (which is the same bit as the phase correction bit) to
  
  signal the least significant bit of a 50/60 fps timecode. See SMPTE ST
  
  12-1:2014 section 12.1.
  Therefore we slightly change the format of the return value of
  
  av_timecode_get_smpte_from_framenum and AV_FRAME_DATA_S12M_TIMECODE and start
  
  using the previously unused Phase Correction bit as Field bit. (As the SMPTE
  
  standard suggests)
  We add 50/60 fps support to av_timecode_get_smpte_from_framenum by calling the
  
  recently added av_timecode_get_smpte function in it which already handles this
  
  properly.
  This change affects the decklink indev and the DV and MXF muxers. MXF has no
  
  fate test for 50/60fps content, DV does, therefore the changes.
  MediaInfo (a recent version) confirms that half-frame timecode must be inserted
  
  to DV. MXFInspect confirms valid timecode insertion to the System Item of MXF
  
  files. For MXF, also see EBU R122.
  Note that for DV the field flag is not used because in the HDV specs (SMPTE
  
  370M) it is still defined as biphase mark polarity correction flag. So it
  
  should not matter that the DV muxer overrides the field bit.
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavutil/timecode.c
  • [DH] libavutil/timecode.h
  • [DH] tests/ref/vsynth/vsynth1-dv-hd
  • [DH] tests/ref/vsynth/vsynth2-dv-hd
  • [DH] tests/ref/vsynth/vsynth3-dv-hd
  • [DH] tests/ref/vsynth/vsynth_lena-dv-hd