can ffmpeg video bit rate option use a multiplier from a txt file as an argument?
Solution 1:
Yes, it is. See https://www.ffmpeg.org/ffmpeg-utils.html - Expression Evaluation.
your external multiplier as multiplier.txt:
2
ffmpeg.bat:
## Read file content into a variable:
set /p multiplier=<multiplier.txt
## Then use the variable as %multiplier%
ffmpeg.exe -i INPUT -b:v %multiplier%*3000k OUTPUT