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• ffmpeg - output 5.1 AAC without lowpass on the LFE channel

  1er janvier 2023, par blendmaster

  I'm trying to encode 6 arbitrary mono audio streams into a single AAC 5.1 track in an mp4 container (here with test streams) :

  


  ffmpeg -f lavfi -i testsrc=duration=10:size=100x100:rate=30 -f lavfi -i aevalsrc="-2+random(0)" -filter_complex "[1:a][1:a][1:a][1:a][1:a][1:a]join=inputs=6:channel_layout=5.1:map=0.0-FL|1.0-FR|2.0-FC|3.0-LFE|4.0-BL|5.0-BR[a]" -map '0:v' -map "[a]" -c:a aac -channel_layout 5.1 -t 10 testlfe.mp4


  


  5 of the channels replicate the input audio just fine (modulo encoding). However, the LFE channel is lowpassed. Extracting with :

  


  ffmpeg -i testlfe.mp4 -filter_complex "channelsplit=channel_layout=5.1:channels=LFE[LFE]" -map '[LFE]' testlfe.wav


  


  I get a lowpassed rumble, instead of the original full white noise

  


  

  


  (from ffmpeg -i testlfe.wav -lavfi showspectrumpic=s=640x320 testlfe.png)

  


  Is there a way to prevent the lowpass from happening ?

  


  I couldn't find any references whether that's inherent to the AAC 5.1 encoding, something that ffmpeg does, or inherent to the decoding process. (I did decode my same test files using something that uses Microsoft MediaFoundation and the LFE channel was still lowpassed).

  


• How do I send buffer to a virtual camera driver ?

  15 juin 2022, par rvega01

  I'm currently working on a project in a Windows environment where I have a Node.js application that accepts an RTSP video stream from a button click and I would like to stream the video data to a virtual camera driver and have it displayed within Microsoft Teams and Skype. The driver that I'm using and have installed (https://github.com/robot9706/VirtualCameraDriver) mentions that the filter implemented in the driver contains a property with a GUID that I can send buffer to.

  


  I was wondering if anyone know of a javascript/node.js library, ffmpeg/gstreamer command, or any solution that comes to mind that can allow me to send video data to that GUID. I have tried outputting the RTSP stream to a videosink with g-streamer but I was unable to specify the display name for the output to be directed to.

  


  With ffmpeg, I was able to find the driver info with DShow but I can only implement the driver as an video input and I'm unable to select the driver as an output through DShow. If there is an gstreamer/ffmpeg solution, please let me know as I'm inexperienced with video streaming and I have looked through many threads here but I'm unable to find an answer.

  


• input : Add a workaround for swscale overread bugs

  22 octobre 2017, par Henrik Gramner

  input : Add a workaround for swscale overread bugs
  swscale can read past the end of the input buffer, which may result in
  
  crashes if such a read crosses a page boundary into an invalid page.
  Work around this by adding some padding space at the end of the buffer when
  
  using memory-mapped input frames. This may sometimes require copying the
  
  last frame into a new buffer on Windows since the Microsoft memory-mapping
  
  implementation has very limited capabilities compared to POSIX systems.
  

  • [DH] input/input.c
  • [DH] input/input.h