If you have an audio or video file with very low volume and the sound is barely audible you can increase it easily with the FFmpeg application. You don’t have to struggle with expensive applications or apps full of ads or spyware. FFmpeg is a powerful and popular open source application which supports almost all audio and video formats and you can do lot of things with it.
Unzip the downloaded file into a directory and open the command prompt (In windows systems type cmd in the Run dialog opened with Windows+R key press)
Type the following command to change to the folder where you unzipped and go to bin folder
Type this command to increase the volume by 200%. Provide the correct location of the input and output files.
ffmpeg -i D:\input.wav -af "volume=2" D:\output.wav
Below command decreases the volume by half.
ffmpeg -i D:\input.wav -af "volume=0.5" D:\output.wav
You may see that the size of the output file may be significantly different than the input file. This could be because the codec type for encoding and bitrate used by FFmpeg may be different compared to the input format.
When you run the command above you can see the codec type and audio bitrate in the output as below. See the highlighted line.
You may want to use the same codec and bitrate as the input file for the same quality and file size.
AAC encoder is used by default in the prebuilt version of FFmpeg which does a decent job. There are newer codecs like He-AAC which provide higher compression but it requires rebuilding FFmpeg from the source due to licensing issues. We will not go into that. I would suggest to use Bitrate of atleast 64kbps for good quality audio.
To set bit rate of 64kbps and twice the volume use the following command
ffmpeg -i D:\input.wav -af "volume=2" -b:a 32k D:\output.wav