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• Copying avcodec parameters

  4 juin 2020, par Ayxan

  I am trying to use libav to convert an MP4 file to an MP3 file. Basically trying to achieve what ffmpeg -i filename.mp4 filename.mp3 does. I've found this official example. But when I run it with an input MP4 and an output MP3 I get an error :

  



  


  Invalid audio stream. Exactly one MP3 audio stream is required.

  


  



  I am not at all familiar with this library but I think I have narrowed the problem down to this line :

  



  ret = avcodec_parameters_copy(out_stream->codecpar, in_codecpar);


  



  It seems to copy all streams for a video file but we only need one for the MP3 file ? I am not sure. There doesn't seem to be a function to copy only the parameters relevant to audio. I checked the sources, avcodec_parameters_copy does a simple memcpy.

  



  Questions :

  



  

  1. Is this the actual problem ?

  


  2. How do I solve it ?

  


  3. Am I on the right track to achieve the goal of extracting audio from a video file ? I've seen this question (and other similar questions like this and this) on here but none seem to have a complete code example. The C API documentation for this library is also a little lacking.

  


  


• OpenCV ffmpeg issues when running Windows 10 app on Windows 7

  1er novembre 2016, par David G.

  I need to maintain a desktop app written in C++, using Qt and OpenCV for some video processing. As far as I understood, the decoding part of OpenCV is delegated to ffmpeg in a separate DLL for licensing reasons.

  The development environment is on Windows 10, using QT Creator and MSVC12 64-bit as compiler. OpenCV version is 3.0, the official distribution. Here, everything runs fine, I am able to decode a video using VideoCapture::open().

  Issues arise when I try to run the application in a standalone fashion with all the required DLLs in the same folder as the .exe file. All cases below are 64-bit OSes.

  On a Windows 10 computer, not the same as the developement machine and no developer libraries present, the video decoding works fine. I have tested on a Windows 8 machine as well, no issues so far.

  On Windows 7, the things get tricky. The same video files that successfully load during the previous tests are not recognized by the app at all i.e. the isOpened call on VideoCapture returns false. For further testing, I stripped the opencv_ffmpeg300_64.dll file to narrow down the issue on Windows 10 and 8 ; as expected, without this DLL the app is no more able to open the same video files.

  It seems that the DLL is simply not recognized on Windows 7.

  • Did you encounter this type of issue and, maybe, have part of a solution ?
  • I would like to monitor which DLLs are loaded as the program runs and see possible "DLL not found" errors. Is it possible, especially on a machine that does not have the entire developement environment ?
  • Can building OpenCV on my own address the issue ?
  • Even further, would it be worth to port the development environment on Windows 7 and build from there ? This requires significant work due to the project itself.

• ERROR : opus not found using pkg-config in msys64 on Windows

  10 août 2022, par prostargamer

  I'm trying to build ffmpeg.

  


  I downloaded msys2 x64 from the official website. This is the latest version.
  
Executed "pacman-Syu", rebooted msys and executed "pacman-Su".

  


  In your file build_ffmpeg_win.sh ffmpeg installs the following packages using pacman :
  

  


  pacman --noconfirm -Sy
pacman --noconfirm -S msys/make
pacman --noconfirm -S mingw64/mingw-w64-x86_64-opus
pacman --noconfirm -S pkg-config
pacman --noconfirm -S diffutils
pacman --noconfirm -S mingw-w64-x86_64-pkg-config


  


  Then I run "pacman -Qet" in order to get the list of packages :

  


  $ pacman -Qet
base 2020.12-1
diffutils 3.8-1
make 4.3-1
mingw-w64-x86_64-opus 1.3.1-4
pkg-config 0.29.2-4


  


  The opus package is installed.

  


  However, when I try to run "build_ffmpeg_win.sh", then I get the following error at the stage ./configure : "ERROR : opus not found using pkg-config"

  


  The following folders and files are located in the "msys64\mingw64\lib" folder :

  


  pkgconfig (folder)
libopus.a
libopus.dll.a


  


  There is an opus.pc file in the msys64\mingw64\lib\pkgconfig folder, the contents of which refer to /mingw64/lib and /mingw64/include.
pkg-config knows about opus, but for some reason this error occurs during ./configure.

  


  How can I solve this problem ?