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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 to live stream from Windows 10 app to Youtube ?

  12 août 2015, par Boland

  I’m playing around with the YouTube Live Stream API. That’s working fine so far, but the next step is to stream the web cam data to YouTube via RTMP.

  In the (excellent) documentation at Google Dev, it outlines the Life of a Broadcast. However, all steps are documented in detail, except the step I’m interested in :

  Step 3.2 : Start your video

  Start transmitting video on your video stream.

  I was able to use Open Broadcasting Software to stream to a manually created YouTube Live Event, but I have no idea how to do it from my Windows 10 App. I’ve looked at the MediaElement class, and was able to capture the web cam preview in my app. But I can only find methods to save as a file.

  Also found information about FFMPEG, which should probably be able to do the job, but I cannot find a library / DLL to use FFMPEG in my App.

  I just need some guidance where to look next, because now I’m just clueless what to do.

  /edit : I came across MPlatform SDK, which sounds exactly what I want, but it costs $5000.... Not for a hobby :(

• C++, FFMpeg : Unable to find any decoder or encoder

  14 juillet 2016, par AmN

  I have been using this sample https://ffmpeg.org/doxygen/trunk/decoding__encoding_8c.html as reference for my C++ application. I have used the same code as in the given page. I have linked the libraries, placed the dlls and compiled with no errors. Everything works except that it always throws : Codec not found error.

  /* find the MPEG-1 video decoder */
  
  codec = avcodec_find_decoder(AV_CODEC_ID_MP2);
  
  if (!codec) {
  
      fprintf(stderr, "Codec not found\n");
  
      exit(1);
  
  }

  I have changed the line to AV_CODEC_ID_MP2 in this, just to test if only the MPEG codex was missing but seems like all are missing. I have tried changing this to multiple codecs as defined in avcodec.h file (enum AVCodecID, line 189), but all return "Codec not found".

  Am I missing something ?

  Compiler : Microsoft Visual Studio 2015 Community Edition
  Project Type : QTProject

  Oh and I am trying to make a Video Player just to enhance my c++ skills during these holidays. First I was trying QTMediaPlayer Widget, but it was throwing crazy errors on "DirectShowPlay::doRender" or something like that. So I switched to FFMpeg, but this too doesn’t work.

  Thank you for reading my question.