Batch-transcribe audio files with whisper.cpp

transcribe.sh

#!/bin/zsh
#
# Batch transcribe audio files with whisper.cpp and ffmpeg
# This script wants:
# - ffmpeg installed and accessible via $PATH
# - whisper.cpp built locally:
#       git clone https://github.com/ggerganov/whisper.cpp
#       cd whisper.cpp
#       make
#   The compiled binary will be called 'main' in the whisper.cpp directory.
#   Set that path in the 'whisper' variable below.

# path to whisper.cpp binary
whisper="/Users/andre/work/whisper.cpp/main"


# uncomment for debugging
# set -x

# command line arguments are:
# - target directory where output files will be written
# - shell glob pattern to match audio input files

# check for required arguments
if [ $# -lt 2 ]; then
    echo "Usage: $0 target_dir pattern"
    echo "e.g.   $0 ~/transcriptions ~/podcasts/*.mp3"
    exit 1
fi

# set target directory and remove $1 from $@
target_dir=$1
shift

# text file that lists previously transcribed files
processed_file=$target_dir/processed.txt

# function to check if a file has already been processed
already_processed() {
    if grep -F -q "$1" $processed_file; then
        echo "Skipping $1"
        return 0
    fi
    return 1
}

# function that calls ffmpeg to convert an audio file to WAV, 16 bit, 16 kHz
convert_to_wav() {
    file=$1
    out_file=$2
    
    echo "Converting $file to $out_file"
    ffmpeg -i "$file" -acodec pcm_s16le -ac 1 -ar 16000 "${out_file}"
}

# function that calls whisper-cpp to transcribe a WAV file
transcribe_with_whisper_cpp() {
    wav_file="${1}"

    # transcribe file
    echo "Transcribing $1"
    "${whisper}" -t 8 -otxt -ovtt -osrt -owts -ocsv -f "${wav_file}"
    echo "${wav_file}" >> $processed_file
}

# move into whisper directory to run whisper-cpp
echo Temporarily moving into $(dirname ${whisper})
pushd $(dirname ${whisper})

# loop over all files matching the pattern
for file in $@; do
    # temporary WAV file
    wav_file="$target_dir/$(basename $file).wav"
    echo "looking for $wav_file..."

    already_processed "$wav_file" && continue

    # convert file to WAV
    convert_to_wav "$file" "${wav_file}"

    # transcribe file
    transcribe_with_whisper_cpp "${wav_file}"

    # clean up wav file
    rm "${wav_file}"
done

popd