#!/bin/bash

# This script converts all MP3 or M4A files in a specified source directory to the Opus format,
# leveraging parallel processing to speed up the conversion.
# Example usage: 
# convert_to_opus.sh source/trimmed_mp3 source/trimmed_opus 8

# Set the source and destination directories from the command-line arguments.
# If no arguments are provided, use default values.
SOURCE_DIR=${1:-source/mp3}
DEST_DIR=${2:-opus_converted}
NUM_JOBS=${3:-$(nproc 2>/dev/null || sysctl -n hw.ncpu)}

# Create the output directory. The -p flag ensures that the command doesn't fail if the directory already exists.
mkdir -p "$DEST_DIR"

export DEST_DIR

# Define the conversion function to be run in parallel.
convert_to_opus() {
  f="$1"
  # Get the base name of the file (e.g., "001.mp3")
  filename=$(basename -- "$f")
  # Get the file name without the extension (e.g., "001")
  filename_noext="${filename%.*}"

  # Use ffmpeg to convert the file to Opus format.
  # The output is redirected to /dev/null to prevent ffmpeg from flooding the console.
  echo "Converting $f to $DEST_DIR/${filename_noext}.opus"
  ffmpeg -i "$f" -fflags +genpts -c:a libopus -ar 48000 -vbr on -map_metadata -1 -y "$DEST_DIR/${filename_noext}.opus" >/dev/null 2>&1
}

export -f convert_to_opus

# Find all .mp3 and .m4a files in the source directory and process them in parallel using a while loop.
find "$SOURCE_DIR" -type f \( -name "*.mp3" -o -name "*.m4a" \) -print0 | while IFS= read -r -d $'\0' file; do
    ((i=i%NUM_JOBS)); ((i++==0)) && wait
    convert_to_opus "$file" &
done
wait

echo "All files have been converted to Opus format and are located in the $DEST_DIR directory."