title: ffmpeg how to shorten volume range
body: <p>I use this command below to get volume information</p>
  <pre><code>ffmpeg -i {fileName} -af  &quot;volumedetect&quot; -f null -
  </code></pre>
  <p>and get result below:</p>
  <pre><code>[Parsed_volumedetect_0 @ 000001b4f9675ec0] mean_volume: -25.1 dB
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] max_volume: -4.0 dB
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_4db: 12
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_5db: 72
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_6db: 293
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_7db: 808
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_8db: 2276
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_9db: 5885
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_10db: 13146
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_11db: 26627
  </code></pre>
  <p>I want to shorten volume range to half range like this below</p>
  <pre><code>[Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_6db: ...
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_7db: ...
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_8db: ...
  [Parsed_volumedetect_0 @ 000001b4f9675ec0] histogram_9db: ...
  </code></pre>
  <p>How to do it by ffmpeg command?</p>
  <p><strong>Update1:</strong></p>
  <p>filename.mp3 volume detect is below:</p>
  <pre><code>[Parsed_volumedetect_0 @ 00000192cd9adcc0] max_volume: -0.3 dB
  [Parsed_volumedetect_0 @ 00000192cd9adcc0] histogram_0db: 32
  [Parsed_volumedetect_0 @ 00000192cd9adcc0] histogram_1db: 333
  [Parsed_volumedetect_0 @ 00000192cd9adcc0] histogram_2db: 1216
  [Parsed_volumedetect_0 @ 00000192cd9adcc0] histogram_3db: 3490
  [Parsed_volumedetect_0 @ 00000192cd9adcc0] histogram_4db: 8829
  [Parsed_volumedetect_0 @ 00000192cd9adcc0] histogram_5db: 19873
  </code></pre>
  <p>after execute command</p>
  <pre><code>ffmpeg -i filename.mp3 -af filename_output.mp3
  </code></pre>
  <p>filename_output.mp3 volume detect is below:</p>
  <pre><code>[Parsed_volumedetect_0 @ 0000017af506dd00] max_volume: -0.4 dB
  [Parsed_volumedetect_0 @ 0000017af506dd00] histogram_0db: 13
  [Parsed_volumedetect_0 @ 0000017af506dd00] histogram_1db: 226
  [Parsed_volumedetect_0 @ 0000017af506dd00] histogram_2db: 906
  [Parsed_volumedetect_0 @ 0000017af506dd00] histogram_3db: 2688
  [Parsed_volumedetect_0 @ 0000017af506dd00] histogram_4db: 7202
  [Parsed_volumedetect_0 @ 0000017af506dd00] histogram_5db: 16473
  </code></pre>
  <p>There is no big changes, if I want to shorten more volume range , how to do?</p>