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• Capture desktop screens including audio with ffmpeg

  9 mars 2019, par klaus

  After referring to the official documentation and one other blog post, I now have following script :

  A="$(pacmd list-sources | grep -PB 1 "analog.*monitor>" | head -n 1 | perl -pe 's/.* //g')"
  
  F="/home/enan/Videos/$(date --iso-8601=minutes | perl -pe 's/[^0-9]+//g').mkv"
  
  V="$(xdpyinfo | grep dimensions | perl -pe 's/.* ([0-9]+x[0-9]+) .*/$1/g')"
  
  ffmpeg -video_size "$V" -framerate 25 -f x11grab -i :0.0 -f pulse -i "$A" -f pulse -i default \
  
      -filter_complex amerge -ac 1 -preset veryfast "$F"

  Basically that script results into the following command :

  ffmpeg -video_size 1366x768 -framerate 25 -f x11grab -i :0.0 -f pulse -ac 2 -i default output.mkv

  In this case, with -ac 2, the audio that gets added with the captured video is of some mic. I’m using a laptop and don’t have a mic, so I don’t exactly know which device the outside sounds get added from but it does. But no audio from the main audio that I can hear through the headphone jack doesn’t get added to the video.

  If I use -ac 1 instead, the video now gets the outside audio as well as the internal audio. That’s good. But how do I restrict the video to only add internal audio, not add audio gotten from mic or something similar.

  I don’t know if it’ll help, but adding it anyway. From man mpv :

         -ac[:stream_specifier] channels (input/output,per-stream)
  
             Set the number of audio channels. For output streams it is set by
  
             default to the number of input audio channels. For input streams this
  
             option only makes sense for audio grabbing devices and raw demuxers and
  
             is mapped to the corresponding demuxer options.

• OpenCV ffmpeg DLL not loaded when running app on Windows 7, works on 8 and 10

  4 avril 2018, 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.

  Edit : Further investigation using Process Explorer clearly shows that the aforementioned DLL is not loaded when the app runs on Windows 7.

  • Is there something specific about how Windows 7 manages the DLL path resolution and eventual security measures ? Seems normal that the first search location is the same folder as the executable, which is the case here.

  I have tried to trace using WinApiOverride32, with no results.

• OpenCV ffmpeg DLL not loaded when running app on Windows 7, works on 8 and 10

  2 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.

  Edit : Further investigation using Process Explorer clearly shows that the aforementioned DLL is not loaded when the app runs on Windows 7.

  • Is there something specific about how Windows 7 manages the DLL path resolution and eventual security measures ? Seems normal that the first search location is the same folder as the executable, which is the case here.

  I have tried to trace using WinApiOverride32, with no results.