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• FFmpeg Matching decibel level between two audio tracks when mixing ?

  9 août 2022, par JohnWick

  I have a collection of mp3 files for various frequencies (i.e. 528hz). I also have a collection of mp3's of ambient background music. So here is the scenario :

  


  I am mixing the tone frequency mp3's with the music mp3's. This works great using the amix filter, no problem. However, some of the ambient music is quiet, which makes the tones sound overpowering. Conversely, some of the ambient music is also fairly loud, making the tones inaudible.

  


  It seems to me, the solution would be to adjust the volume of the tone to match the decibel level of the associated music track. How can this be done programmatically ? Perhaps parsing the output of a ffprobe call, but at that point I wouldn't quite be sure how to proceed towards my goal. I figured reaching out on Super User might save me a ton of pain, by turning to more experienced ffmpeg users. Maybe my approach is also flawed, and would be happy if someone can suggest a better method to achieve what I am looking for.

  


  Here is my python code so far.

  


  import ffmpeg
import os

tones = os.listdir('tones')
songs = os.listdir('music')

for tone in tones:
    for song in songs:
        tone_in = ffmpeg.input(f'tones/{tone}', stream_loop=-1)
        music_in = ffmpeg.input(f'music/{song}')
        mixed = ffmpeg.filter([tone_in, music_in], 'amix', inputs=2, duration='shortest')
        out = ffmpeg.output(mixed, f'output/{tone} {song}.mp3')
        out.run()


  


• iPhone - A problem with decoding H264 using ffmpeg

  25 mars 2012, par HAPPY_TIGER

  I am working with ffmpeg to decode H264 stream from server.

  I referenced DecoderWrapper from http://github.com/dropcam/dropcam_for_iphone.

  I compiled it successfully, but I don't know how use it.

  Here are the function that has problem.

  - (id)initWithCodec:(enum VideoCodecType)codecType 
  
           colorSpace:(enum VideoColorSpace)colorSpace 
  
                width:(int)width 
  
               height:(int)height 
  
          privateData:(NSData*)privateData {
  
      if(self = [super init]) {
  
  
  
          codec = avcodec_find_decoder(CODEC_ID_H264);
  
          codecCtx = avcodec_alloc_context();
  
  
  
          // Note: for H.264 RTSP streams, the width and height are usually not specified (width and height are 0).  
  
          // These fields will become filled in once the first frame is decoded and the SPS is processed.
  
          codecCtx->width = width;
  
          codecCtx->height = height;
  
  
  
          codecCtx->extradata = av_malloc([privateData length]);
  
          codecCtx->extradata_size = [privateData length];
  
          [privateData getBytes:codecCtx->extradata length:codecCtx->extradata_size];
  
          codecCtx->pix_fmt = PIX_FMT_YUV420P;
  
  #ifdef SHOW_DEBUG_MV
  
          codecCtx->debug_mv = 0xFF;
  
  #endif
  
  
  
          srcFrame = avcodec_alloc_frame();
  
          dstFrame = avcodec_alloc_frame();
  
  
  
          int res = avcodec_open(codecCtx, codec);
  
          if (res < 0)
  
          {
  
              NSLog(@"Failed to initialize decoder");
  
          }
  
      }
  
  
  
      return self;    
  
  }

  What is the privateData parameter of this function ? I don't know how to set the parameter...

  Now avcodec_decode_video2 returns -1 ;

  The framedata is coming successfully.

  How solve this problem.

  Thanks a lot.

• How to create a custom processor for audio files in Ruby on Rails(5) with Paperclip

  17 juillet 2017, par Thomas Roest

  So I’m trying to convert mp3 files into .flac with Paperclip custom processors and ffmpeg. The following code runs the ffmpeg command and creates a temporary flac file. However, it is not saved ? Currently only the original file is saved. What am I missing here ?

  class AudioFile < ApplicationRecord
  
    has_attached_file :raw_audio, processors: [:custom], styles: { original: {}}

  the custom processor

  module Paperclip
  
   class Custom < Processor
  
  
  
    def initialize(file, options = {}, attachment = nil)
  
      super
  
      @file = file
  
      @basename = File.basename(@file.path)
  
      @format = options[:format] || 'flac'
  
      @params = options[:params] || '-y -i' 
  
    end
  
  
  
    def make
  
      source = @file
  
      output = Tempfile.new([@basename, ".#{@format}"])
  
      begin
  
        parameters = [@params, ':source',':dest'].join(' ')
  
        Paperclip.run('ffmpeg', parameters, :source => File.expand_path(source.path), :dest => File.expand_path(output.path), :sample_rate => @sample_rate, :bit_rate => @bit_rate)
  
      end
  
     output
  
    end
  
  
  
   end
  
  end