Boosting audio volume in a video file

For some reason I'm finding that some video files played directly on my new Samsung TV (by mounting a USB drive) have a low volume and boosting the TV's volume beyond 40 (of presumably 100) yields no additional gain.

This ffmpeg command can be used to boost the volume in the file:

ffmpeg -i myvideo.mkv -vcodec copy -af "volume=12dB" myvideo-boosted.mkv

You can vary the boost by chaning the volume gain parameter. I found 12dB was about right. Negative values are allowed also.