Q:

Increase Audio Volume of MOV-Video in OS X

I have a MOV-Video file and I want to increase the volume of the audio layer without reencoding the entire video.
Is there a way to solve this problem?

A:

One thing you can do is use a video viewer like IINA on macOS, which allows you to go beyond the 100% volume limit. It allows you to set the volume up to 1000%, so if you are trying to view an unusually quiet video, you can increase the volume in IINA without having to crank up your computer's volume too much.
In IINA: You can set maximum volume (100-1000%) in Preference, and use ↑ to set volume larger than 100%.

