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• FFmpeg : How to create dynamic volume changes in an audio file ?

  14 octobre 2018, par Ankush

  I am working on a project in which I need to change the volume of an audio file dynamically.

  Let’s say, I have an audio file with name xyz.mp3 (20 - seconds audio file).
  I need to set the volume in it like :

  Time Range (in Seconds)     ||     Volume Percentage (in %)
  
  -------------------------------------------------------------------    
  
      0 - 4                   ||           100
  
                              ||
  
      4 - 8                   ||    change from 100 - 20 (dynamically)
  
                              ||
  
      8 - 12                  ||           20
  
                              ||           
  
      12 - 16                 ||    change from 20 - 100 (dynalically)
  
                              ||
  
      16 - 20                 ||           100       

  Now, I know that to change the volume for a particular time in audio, I can use the following command :

  ffmpeg -i in.mp3 -af volume=20:enable='between(t,8,12)' out.mp3

  but when I use volume effect, it does not change the volume dynamically. It just straightly change volume from 100 to 20 and not change it like fading.

  and When I use afade command like :

  ffmpeg -i in.mp3 -af afade=t=in:ss=4:d=8,afade=t=out:st=12:d=16 out.mp3

  or

  ffmpeg -i in.mp3 -af afade=enable='between(t,4,8)':t=in:ss=4:d=4,afade=enable='between(t,12,16)':t=out:st=12:d=4 out.mp3

  but it looks that afade does not work multiple times even when I am using ffmpeg 3.0.1 version.

  As afade only works single time, I had also split my audio into parts of 4 second and add fade effects to it and then combine them again, but there is some milliseconds gap comes between each clip. Does anyone know a better way to do it ? Please help me...

  Update 1 :

  Here is that code I used :

  "volume='" +
  
              "between(t,0,8)+(1-0.8*(t-8)/4)*" +        // full
  
              "between(t,8.01,11.99)+0.1*" +             // change from HIGH -> LOW
  
              "between(t,12,16)+(0.1+0.8*(t-16)/4)*" +   // low
  
              "between(t,16.01,19.99)+1*" +              // change from LOW -> HIGH   -
  
              "between(t,20,24)+(1-0.8*(t-24)/4)*" +     // full
  
              "between(t,24.01,27.99)+0.1*"+             // change from HIGH -> LOW   -
  
              "between(t,28,32)+(0.1+0.8*(t-32)/4)*" +   // low
  
              "between(t,32.01,35.99)+1*" +              // change from LOW -> HIGH  -
  
              "between(t,36,40)+(1-0.8*(t-40)/4)*" +     // full
  
              "between(t,40.01,43.99)+0.1*"+             // change from HIGH -> LOW   -
  
              "between(t,44,48)+(0.1+0.8*(t-48)/4)*" +   // low
  
              "between(t,48.01,51.99)+" +                // change from LOW -> HIGH -
  
              "between(t,52,56)" +                       // high
  
              "':eval=frame";

  In this code, I got a small (some milliseconds gap) at those places where I initialize the audio to change the volume

  Update 2
  Ok I got it, I just need to change the time values like 19.99 to 19.9999 and 16.01 to 16.0001 and it solve the problem. Thank You Gyaan Sir.

• atomics : cosmetics : Restructure ifdefs for greater clarity

  18 décembre 2013, par Diego Biurrun

  atomics : cosmetics : Restructure ifdefs for greater clarity
  Also fix the #endif comment in a few places and #include config.h to
  
  avoid assuming it is #included implicitly.
  

  • [DBH] libavutil/atomic.c
  • [DBH] libavutil/atomic.h

• FFMPEG using a screen capture for an overlay results in serious visual flaws

  3 octobre 2017, par Joey

  I’m trying to overlay a screen capture of a specific window on top of a background image, and output the result - it works but results in unacceptable visual flaws.

  The command I’m using is :

  ffmpeg -loop 1 -r 30 -i background.jpg -f gdigrab -r 30 -i title=Calculator \
  
  -filter_complex "[0:v][1:v]overlay=10:10[video]" -map "[video]" -c:v libx264 \
  
  -f flv output.flv

  which places a screencap of the calculator window on the background at position 10,10.

  This is what the output looks like :

  

  All the buttons on the calculator are super muddied and appear bold, almost as if it was overlaid several times at slightly different positions. Is there something wrong with the command or any way to fix it and preserve visual integrity of the original ? Changing the output format doesn’t have any effect, nor does setting -crf 0 or adjusting any other encoding settings.

  This doesn’t happen when I screen capture just the calculator by itself without overlaying it on anything. For reference here is what the output looks like when I only record the calculator with no overlaying :