how do I use ffmbc to decrease the input video volume by 5dB?
FFmpeg has option 'volume' that accepts values like '2' for multiplying by 2 and '-12dB' for volume decrease by 12dB.
In FFmbc I tried option 'vol' but it seems to take only the number into consideration. I read somewhere that '256' is the default value for the output audio be the same level as the input. '512' doubles the audio level. But '-12dB' gets you a very silent video, like setting the option just to '12'.