General (lossy) method for normalizing volume of any video file

I have an MKV video file (H264 video, AC3 audio) whose volume I need to normalize. Unfortunately, there doesn't seem to be any lossless way of normalizing the AC3 audio track. So I found out the general (lossy) way of normalizing the audio track of any video file is:

> ffmpeg -i input.mkv -vol nnn -vcodec copy output.mkv

nnn = 256 (no change)
nnn = 128 (half the volume)
nnn = 512 (double the volume)
etc.

This should work for any video file format that ffmpeg recognizes.

In addition, I can use the -map commands to remove any unwanted subtitles.

> ffmpeg -i input.mkv -map 0:0 -map 0:1 -ac 2 -vol nnn -vcodec copy output.mkv

This tells ffmpeg to only include track 0 (video) and 1 (audio) in the output file and ignore the rest.

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Volume normalization of MP3 audio track in AVI video files

For AVI video files with MP3 audio tracks, the best way to normalize its volume without recompression involves using FFMpeg and MP3Gain:

> ffmpeg -i input.avi -vn -acodec copy -y audio.mp3
> ffmpeg -i input.avi" -an -vcodec copy -y video.avi
> mp3gain /r audio.mp3
> ffmpeg -i audio.mp3 -i video.avi -acodec copy -vcodec copy -y output.avi

In fact, AACGain in the previous post could substitute for MP3Gain as well.

So the process basically involves extracting the audio and video tracks separately from the original video file, normalizing the audio track using MP3Gain, then muxing the audio (normalized) and video tracks back again.

Since everything is command-line driven, it will be quite straightforward to create a batch/script file that performs all 4 steps in sequence.

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Volume normalization of audio track in MP4 video files

I am currently looking at how to "normalize" the volume of various video files without recompression, and documenting my findings here.

For MP4 video files, an easy solution appears to be AACGain, a command line utility that handles AAC audio. Simply run:

    aacgain /r *.mp4

and all MP4 video files will be normalized. The process is entirely reversible (using the /u command), and involves no recompression at all.

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