Transcribe MP3 files using Mistral's Voxtral API with speaker diarization

mp3-to-text

#!/usr/bin/env python3
import json
import os
import sys

from mistralai import Mistral


def format_time(seconds):
    minutes = int(seconds) // 60
    secs = int(seconds) % 60
    return f"{minutes:02d}:{secs:02d}"


def transcribe(audio_file):
    client = Mistral(api_key=os.environ["MISTRAL_API_KEY"])

    with open(audio_file, "rb") as f:
        response = client.audio.transcriptions.complete(
            model="voxtral-mini-latest",
            file={
                "file_name": os.path.basename(audio_file),
                "content": f,
            },
            diarize=True,
            timestamp_granularities=["segment"],
        )

    return json.loads(response.model_dump_json())


def format_transcript(data):
    segments = data["segments"]

    merged = []
    for seg in segments:
        if merged and seg["speaker_id"] == merged[-1]["speaker_id"]:
            merged[-1]["end"] = seg["end"]
            merged[-1]["text"] += " " + seg["text"].strip()
        else:
            merged.append({
                "speaker_id": seg["speaker_id"],
                "start": seg["start"],
                "end": seg["end"],
                "text": seg["text"].strip(),
            })

    lines = []
    for seg in merged:
        start = format_time(seg["start"])
        end = format_time(seg["end"])
        lines.append(f"{seg['speaker_id']} {start}-{end}: {seg['text']}")

    return "\n".join(lines) + "\n"


def main():
    if len(sys.argv) < 2:
        print(f"Usage: {sys.argv[0]} <audio_file> [output.txt]", file=sys.stderr)
        sys.exit(1)

    audio_file = sys.argv[1]
    if not os.path.isfile(audio_file):
        print(f"Error: file not found: {audio_file}", file=sys.stderr)
        sys.exit(1)

    print(f"Transcribing {audio_file}...", file=sys.stderr)
    data = transcribe(audio_file)
    output = format_transcript(data)

    if len(sys.argv) >= 3:
        with open(sys.argv[2], "w") as f:
            f.write(output)
        print(f"Written to {sys.argv[2]}", file=sys.stderr)
    else:
        print(output, end="")


if __name__ == "__main__":
    main()