FFMPEG调节音频的音量大小，混音

找了很久，国内网站没有，最后还是用google到ffmpeg论坛，找到了。
http://ffmpeg.gusari.org/viewtopic.php?f=25&t=517
防止论坛倒闭，在这里备份下：

 How to change audio volume up / down with FFmpeg?

by screenshaper »
Thu Oct 16, 2014 6:50 pm 

This thread is OUTDATED

Later -af option has been implemented!

Now this command

CODE: SELECT ALL

ffmpeg
-i input.wav -af volume=-3dB output.wav

is perfectly working

See ticket #725

这个就是volume减掉3db。

还有一种：

To increase the volume with 

ffmpeg

 use
the commad: 

ffmpeg -i input.wav -af 'volume=2' output.wav

Replace 

volume=X

 with
a suitable number. For example 0.5 will half, 2 will double the volume.

========================

To get volume level of the media file in command line I use:

ffmpeg -i audo.mp3 -af "volumedetect" -f null /dev/null

in the output I see something like this:

[Parsed_volumedetect_0 @ 0000000004087260] n_samples: 41316480
[Parsed_volumedetect_0 @ 0000000004087260] mean_volume: -22.5 dB
[Parsed_volumedetect_0 @ 0000000004087260] max_volume: -5.8 dB
[Parsed_volumedetect_0 @ 0000000004087260] histogram_5db: 3
[Parsed_volumedetect_0 @ 0000000004087260] histogram_6db: 892
[Parsed_volumedetect_0 @ 0000000004087260] histogram_7db: 8686
[Parsed_volumedetect_0 @ 0000000004087260] histogram_8db: 36098