Collecting ffmpeg snippets that work for me and converting them to reusable scripts.

caudio

#!/usr/bin/env bash

set -e

gain=${3-"1"}

if [ "$#" -lt 2 ]; then
  echo "Usage: $0 input.aifc output.aifc [gain=2]"
  exit 1
else
  ffmpeg -i $1 -filter_complex acompressor=level_in=$gain $2 -y
  exit 0
fi

caudio_multiple

#!/usr/bin/env bash

set -e

while [[ $# -gt 1 ]]
do
key="$1"

case $key in
    -h|--help)
    helping=YES
    shift # past argument
    ;;
    -x|--suffix)
    suffix="$2"
    shift # past argument
    ;;
    -s|--searchpath)
    search_path="$2"
    shift # past argument
    ;;
    -g|--gain)
    gain="$2"
    shift # past argument
    ;;
    *)
          # unknown option
    ;;
esac
shift # past argument or value
done

# if [[ "YES" -eq $helping ]]; then
#   echo "Usage: $0 [-x|--suffix _c] [-s|--searchpath ./*] [-g|--gain 2] [-h|--help]"
#   exit 1
# else
  suffix=${suffix-"_c"}
  search_path=${search_path-"./*"}
  gain=${gain-"2"}

  echo
  echo "Converting files in search_path: ${search_path}, appending suffix: ${suffix}, with gain: ${gain}."
  echo

  for fullfile in $search_path; do
    # filename=$(basename "$fullfile")
    extension="${fullfile##*.}"
    filename="${fullfile%.*}"
    target_filename="$filename$suffix.$extension"
    command="ffmpeg -i $fullfile -filter_complex acompressor=level_in=$gain $target_filename -y"
    echo "Executing: $command"
    echo
    $command
    # echo $target_filename
  done

  exit 0

# fi

compose_at_frame_rate

#!/usr/bin/env bash

set -e

prefix=${3-"img_"}
suffix=${4-"jpg"}

if [ "$#" -lt 2 ]; then
  echo "Usage: $0 frame_rate output.mp4 [prefix=img_] [suffix=jpg]"
  exit 1
else
  ffmpeg -framerate $1 -i $prefix%03d.$suffix -c:v libx264 -r 30 -pix_fmt yuv420p $2
  exit 0
fi

extract_every_n_frames

#!/usr/bin/env bash

set -e

if [ "$#" -ne 3 ]; then
  echo "Usage: $0 input.mp4 output_directory n"
  exit 1
else
  mkdir $2
  ffmpeg -i $1 -vf "select=not(mod(n\,$3))" -vsync vfr -q:v 2 $2/img_%03d.jpg
  exit 0
fi

generic2mp3

#!/usr/bin/env bash

set -e

if [ "$#" -ne 2 ]; then
  echo "Usage: $0 input output.mp3"
  exit 1
else
  ffmpeg -i $1 -acodec libmp3lame -ab 128k $2
  exit 0
fi

gif2mp4

#!/usr/bin/env bash

set -e

if [ "$#" -ne 2 ]; then
  echo "Usage: $0 input.gif output.mp4"
  exit 1
else
  ffmpeg -i $1 -movflags faststart -pix_fmt yuv420p -vf "scale=trunc(iw/2)*2:trunc(ih/2)*2" $2
  exit 0
fi

gif_maker

#!/bin/sh

# Control the start and duration
# start_time=2:00
# duration=45

palette="/tmp/palette.png"

# Larger format
filters="fps=15,scale=640:-1:flags=lanczos"

# Test version
# filters="fps=15,scale=320:-1:flags=lanczos"

# Higher quality with the trim filter
# filters="trim=start_frame=12:end_frame=431,fps=15,scale=320:-1:flags=lanczos"


ffmpeg -v warning -i $1 -vf "$filters,palettegen" -y $palette
ffmpeg -v warning -i $1 -i $palette -lavfi "$filters [x]; [x][1:v] paletteuse" -y $2

# Use the start and duration
# ffmpeg -v warning -ss $start_time -t $duration -i $1 -vf "$filters,palettegen" -y $palette
# ffmpeg -v warning -ss $start_time -t $duration -i $1 -i $palette -lavfi "$filters [x]; [x][1:v] paletteuse" -y $2

m4a2mp3

#!/usr/bin/env bash

set -e

if [ "$#" -ne 2 ]; then
  echo "Usage: $0 input.m4a output.mp3"
  exit 1
else
  ffmpeg -i $1 -acodec libmp3lame -ab 128k $2
  exit 0
fi

mkv2mp3

#!/usr/bin/env bash

set -e

if [ "$#" -ne 2 ]; then
  echo "Usage: $0 input.mkv output.mp3"
  exit 1
else
  ffmpeg -i $1 -acodec mp3 -vcodec mpeg4 -qscale 0 /tmp/mkv2mp3.avi -y
  ffmpeg -i /tmp/mkv2mp3.avi $2
  rm /tmp/mkv2mp3.avi
  exit 0
fi

naudio

#!/usr/bin/env bash

set -e

if [ "$#" -lt 2 ]; then
  echo "Usage: $0 input_filename output_filename"
  echo "    input file is best if compressed with gain=1"
  exit 1
else

  # Use ffmpeg to get the max volume
  max_volume=`ffmpeg -i $1 -af "volumedetect" -f null /dev/null 2>&1 | grep max_volume | awk '{print $5}'`

  # Get the amount to increase the volume
  gain=`python -c "print($max_volume * -1)"`"dB"

  # Normalize the audio
  ffmpeg -i $1 -af "volume=$gain" $2

  exit 0
fi

rename_files

#!/usr/bin/env bash

set -e

prefix=${1-"img_"}
suffix=${2-"jpg"}

if [ "-h" == "$1" ]; then
  echo "Usage: $0 [prefix=img_] [suffix=jpg]"
  exit 1
else
  for i in *.$suffix; do
    new=$(printf "$1%03d.$suffix" "$a")
    mv -- "$i" "$new"
    let a=a+1
  done
  exit 0
fi

webm2mp4

#!/usr/bin/env bash

set -e

if [ "$#" -ne 2 ]; then
  echo "Usage: $0 input.webm output.mp4"
  exit 1
else
  ffmpeg -fflags +genpts -i $1 -r 24 $2
  exit 0
fi