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• lavfi/vf_libplacebo : allow linking to shared library with dllimport

  17 mai 2023, par Kacper Michajłow

  lavfi/vf_libplacebo : allow linking to shared library with dllimport
  Address of dll imported variables can't be used for constant
  
  initialization in C language modes.
  

  • [DH] libavfilter/vf_libplacebo.c

• FFMPEG to remove audio but keeping background sound

  17 octobre 2022, par Sushil

  I am trying to add voice over to the existing video which has some audio in English and some background sound. I am trying to add other than English audio on top of it and keeping background sound. But when I add new audio it removes all the background sound and when it adds new audio which makes it robotic as original background sound is lost.
When I add new audio by using amix filter, it keeps all sound like English and new language both, and both plays together.

  


  

  1. Is there any way to separate background sound and speaking audio from video separately ?

  


  2. Is it possible to mute or remove audio from only parts of video like offset between time frames ?

  


  


  Command that I am using for add new audio
ffmpeg  -i independance_speech.mp4  -i 01.mp3 -filter_complex "[1]adelay=10000[s1];[s1]amix=inputs=2[a]" -map 0:v  -map "[a]" -c:v copy result.mp4

  


• FFmpeg : stream audio playlist, normalize loudness and generate spectrogram and waveform

  23 février 2021, par watain

  I would like to use FFmpeg to stream a playlist containing multiple audio files (mainly FLAC and MP3). During playback, I would like FFmpeg to normalize the loudness of the audio signal and generate a spectrogram and waveform of the audio signal separately. The spectrogram and waveform should serve as a audio stream monitor. The final audio stream, spectrogram and waveform outputs will be sent to a browser, which plays the audio stream and continuously renders the spectrogram and waveform "images". I would also like to be able to remove and add audio files from the playlist during playback.

  



  As a first step, I would like to use the ffmpeg command to achieve the desired result, before I'll try to write code which does the same programmatically.

  



  (sidenote : I've discovered libgroove which basically does what I want, but I would like to understand the FFmpeg internals and write my own piece of software. The target language is Go and using either the goav or go-libav libraries might do the job. However, I might end up writing the code in C, then creating Go language bindings from C, instead of relying on one of the named libraries.)

  



  Here's a little overview :

  



  playlist (input) --> loudnorm --> split --> spectrogram --> separate output
                                    |
                                  split ---> waveform ----> separate output
                                    |
                                    +------> encode ------> audio stream output


  



  For the loudness normalization, I intend to use the loudnorm filter, which implements the EBU R128 algorithm.

  



  For the spectrogram, I intend to use the showspectrum or showspectrumpic filter. Since I want the spectrogram to be "steamable", I'm not really sure how to do this. Maybe there's a way to output segments step-by-step ? Or maybe there's a way to output some sort of representation (JSON or any other format) step-by-step ?

  



  For the waveform, I intend to use the showwaves or showwavespic filter. The same as for the spectrogram applies here, since the output should be "streamable".

  



  I'm having a little trouble to achieve what I want using the ffmpeg command. Here's what I have so far :

  



  ffmpeg \
    -re -i input.flac \
    -filter_complex "
      [0:a] loudnorm [ln]; \
      [ln] asplit [a][b]; \
      [a] showspectrumpic=size=640x518:mode=combined [ss]; \
      [b] showwavespic=size=1280x202 [sw]
    " \
    -map '[ln]' -map '[ss]' -map '[sw]' \
    -f tee \
    -acodec libmp3lame -ab 128k -ac 2 -ar 44100 \
    "
      [aselect='ln'] rtp://127.0.0.1:1234 | \
      [aselect='ss'] ss.png | \
      [aselect='sw'] sw.png
    "


  



  Currently, I get the following error :

  



  Output with label 'ln' does not exist in any defined filter graph, or was already used elsewhere.


  



  Also, I'm not sure whether aselect is the correct functionality to use. Any Hints ?