title: Adjust volume of both input mp3 files while merging using ffmpeg
body: <p>I am using the following command to merge two audio files (mp3) into one output.mp3</p>
  
  <pre><code>-i /sdcard/NNR/input1.mp3 -i /sdcard/NNR/input2.mp3 
      -filter_complex amerge -ac 2 -c:a libmp3lame 
      -q:a 4 /sdcard/NNR/output.mp3
  </code></pre>
  
  <p>Kindly suggest me how to adjust volume level of both input files to some specific level.</p>
  
  <p>I have found the following filter variable but don't exactly know how to adjust into my command.</p>
  
  <pre><code>ffmpeg -i a.mp3 -i b.mp3 
     -filter_complex "[0:a]volume=.25[A];[1:a][A]amerge[out]" 
     -map [out] -c:a pcm_s16le out.wav
  </code></pre>
  
  <p>Any help will be much appreciated.Thanks</p>