Adding metadata to opus file from command line

You should try something like:

flac -c -d -force-raw-format --endian=little --signed=unsigned input.flac | \
  lame -r --little-endian --unsigned \
       -s 44.1 [other encoding options here] - output.mp3

On the flac side:

• -c means output to stdout
• -d decode
• -force-raw-format --endian=little --signed=unsigned force RAW, little-endian, unsigned output

On the lame side:

• - read from stdin (this is nearly standard)
• -r read RAW pcm data
• --little-endian --unsigned match what lame outputs
• -s frequency: match that parameter with what your flac file contains
• You might need --bitwidth if your flac file isn't 16bits/sample

Concerning the endian-ness and signed-ness, not sure what the "native" format you have is (or how to determine that) - try a few combinations. As long as they match on both sides of the pipe, picking the wrong one should only cost CPU time.

You should decompose your goal into several steps easier to solve. This will have two advantages:

• It will be easier to solve,
• The resulting code will be clearer and more reusable.

The scripts below basically follows these steps:

1. Generate raw statistic files. An easy way is to append the file size and the file name in a temporary file named after the original file extension. So, if you have the file /path/to/foo.mp3 which is 3000000 large, it will append 3000000 /path/to/foo.mp3 at the end of a temporary file named mp3.
2. Handle specific cases. Here it will process the temporary file m4a and create the two other files m4a_aac and m4a_alac based on the test you gave in the question.
3. Generate output. All the needed information being now available, it just has to:
   • Count the number of line in each temporary file to determine the number of file of this type,
   • Sum up each size to get the total size of files of this type.

Here is the script:

#!/bin/sh

# This script takes the searched directory as first parameter.
# For instance: ./this-script.sh ~/Music

: ${1:?"You must pass the search directory as first parameter."}
searchdir="$1"

# Create a temporary directory
statsdir=""
trap 'rm -rf $statsdir' EXIT
statsdir=$(mktemp -d "/tmp/tmp.XXXXXXXXXX") || exit 1

# Generate one listing file per extension
awkscript='/\.[[:alnum:]]+$/ {print $0 >statsdir"/"$(NF)}'
# For Linux: stat -c "%s %n"
# For Mac: stat -f "%z %N"
find "$searchdir" -type f -exec stat -f "%z %N" {} + | \
    awk -F '.' -v statsdir="$statsdir" "$awkscript"

# Distinguish between m4a/AAC and m4a/ALAC
if [ -f "$statsdir/m4a" ]; then
    input="$statsdir/m4a"
    while IFS= read -r line; do
        filename=${line#* }
        if avprobe "$filename" 2>&1 | grep -q 'Audio: alac'; then
            echo "$line" >> "$statsdir/m4a_alac"
        else
            echo "$line" >> "$statsdir/m4a_aac"
        fi
    done < "$input"
    rm "$statsdir/m4a"
fi

# Generate and display result
{
    printf "Type Count Size\n"
    for extension in $(ls "$statsdir"); do
        count=$(wc -l "$statsdir/$extension" | cut -d ' ' -f 1)
        totalsize=$(awk '{s+=$1} END {print s}' "$statsdir/$extension")
        printf "%s %d %d\n" "$extension" "$count" "$totalsize"
    done
} | column -t