#!/bin/sh
##
## SCRIPT: 00_ffmpeg_mp4_CHG_AUDIO_VOLUME.sh
##
## PURPOSE: Change the audio volume of a '.mp4' movie file.
##
## METHOD OF USE: 
##   1) Put this script in the directory of '.mp4' movie files
##      that you want to clip.
##   2) Edit this script to set the input & output filenames and volume level.
##   3) Run the script in a terminal window positioned at the directory
##      that holds this script and the movie files.
##
## REFERENCE:
## https://trac.ffmpeg.org/wiki/AudioVolume
## 
## Examples:
## 
## If we want our volume to be half of the input volume:
## 
##    ffmpeg -i input.wav -filter:a "volume=0.5" output.wav
## 
## 150% of current volume:
## 
##    ffmpeg -i input.wav -filter:a "volume=1.5" output.wav
##
## You can also use decibel measures. To increase the volume by 10dB:
## 
##    ffmpeg -i input.wav -filter:a "volume=10dB" output.wav
## 
## To reduce the volume, use a negative value:
## 
##    ffmpeg -i input.wav -filter:a "volume=-5dB" output.wav
## 
## Script started: 2021jul16
##
   

ffmpeg \
   -i input_40sec_640x480_LOWLOWvol_h264-aac.mp4 \
   -filter:a "volume=15.5" \
   output_40sec_640x480_h264-aac.mp4
    
##  00_temp.mp4   
 
# totem 00_temp.mp4
# ffplay 00_temp.mp4

exit