Change video volume

Two different fixes

Raising the volume multiplies the whole waveform. That works when a recording is uniformly too quiet, and it fails when the recording is uneven — because it raises the loud parts by exactly as much as the quiet ones, and the loud parts hit the ceiling and distort.

Evening out the levels is the other option, and it is usually the right one. Rather than scaling everything, it targets a consistent perceived loudness, bringing quiet passages up and loud ones down. A recording where one person sat close to the microphone and another sat across the room becomes listenable.

How far you can push it

Up to about 200% is usually safe. Beyond roughly 300% most recordings start to clip audibly, because the peaks run out of headroom. If a recording needs more than that, the problem is the recording rather than the level, and evening out is more likely to help than amplifying.

Setting the volume to 0% silences the audio while keeping the track — different from muting, which removes the track entirely.

The video is untouched

Only the audio is re-encoded; the video stream is copied straight through. So this is fast even on a long file, and costs nothing in picture quality.

Amplifying does not recover detail

Worth being clear: turning up a recording made too far from the microphone amplifies the room noise along with the voice. It gets louder, not clearer. Nothing can undo the distance.

Related

For audio files on their own, normalise audio volume does the same evening-out with more control over the target.