fan_transcribe

Fan out audio transcription tasks via OpenAI Whisper and Modal Labs.

OpenAI Whisper is a tool for running audio transcriptions, but it's not especially fast to run on a local machine.

This project provides a command line wrapper around Whisper that allows you to fan out transcription tasks to a cluster of machines provisioned by Modal. Additionally, it also provides an easy way to expose that entrypoint as a web service.

The key idea here is that you can first use ffmpeg to break up an audio file by gaps of silence, then you can transcribe each of those chunks in parallel on a managed set of containers.

Modal's workflow allows you to describe system images, define remote functions, mount shared volumes and execute code across managed runtimes, all from a local python context. Notably, it makes it easy to associate a function invocation to a managed container, allowing us to fan out a bunch of similar compute tasks in duplicate runtimes by simply mapping a set of arguments over a function reference.

Benchmarks

The following are benchmark results from running the medium.en model on a ~1h30m audio file:

Environment	Runtime	Segments	Concurrency	Cost
M1 Pro laptop	9:40:54	1	1	n/a
Modal CPU	0:03:35	254	~258 Containers	$2.61
Modal t4 GPU	0:07:55	254	~14 Containers	$1.24
Modal a10g GPU	0:03:49	254	~22 Containers	$1.49
Modal CPU	0:03:28	508	~345 Containers	$4.09

Practically, I have been finding the base and tiny models to be good enough, and those will run about 8-16x faster and mostly cost < $0.08 for the same file.

Usage

You should have a Modal account and have the modal CLI installed and set up with a token.

After that, you can use the main fan_transcribe.py module from a shell:

$ python fan_transcribe.py -h                                                

usage: fan_transcribe.py [-h] [-i FILENAME] [-u URL] [-o OUT] [-m MODEL] [-g GPU] [-sg MIN_SEGMENT_LEN] [-sl MIN_SILENCE_LEN] [-f]

options:
  -h, --help            show this help message and exit
  -i FILENAME, --filename FILENAME
                        a local file to transcribe
  -u URL, --url URL     optional remote url of an audio file to transcribe
  -v VIDEO_URL, --video_url VIDEO_URL
                        optional remote url of a video to transcribe (supports most video streaming sites)
  -o OUT, --out OUT     optional output directory for transcription results. defaults to ./transcripts/ NB: unless you suffix this arg with .json, it will be interpreted as a
                        directory
  -m MODEL, --model MODEL
                        model to use for transcription. defaults to base.en. model options: [tiny.en, tiny, base.en, base, small.en, small, medium.en, medium, large, large-v1,
                        large-v2]
  -g GPU, --gpu GPU     optional GPU to use for transcription. defaults to None. GPU options: [t4, a100, a100-20g, a10g, any]
  -sg MIN_SEGMENT_LEN, --min_segment_len MIN_SEGMENT_LEN
                        minimum segment length (in seconds) for fan out. defaults to 5.0
  -sl MIN_SILENCE_LEN, --min_silence_len MIN_SILENCE_LEN
                        minimum silence length (in seconds) to split on for segment generation. defaults to 2.0
  -f, --force           re-run a job identifier even if it's already processed

Example CLI usage:

$ python fan_transcribe.py -i test.mp3
$ python fan_transcribe.py -u https://example.com/test.mp3
$ python fan_transcribe.py -v https://youtube.com/watch?v=1234 # or any other video streaming site

$ python fan_transcribe.py -i ~/docs/test.mp3 -m base.en -o ./xcribe/
$ python fan_transcribe.py -i test.mp3 --min_segment_len 30 --min_silence_len 2
$ python fan_transcribe.py -i test.mp3 --gpu t4
$ python fan_transcribe.py -i already-processed.mp3 --min_silence_len 3 -f

Alternatively, you can use modal's deployment commands to expose a web endpoint:

$ modal deploy api.py # or modal serve api.py

# then you can make requests to the endpoint:

$ curl -X "POST" "https://<your-endpoint-url>.modal.run" \
     -H 'Content-Type: application/json; charset=utf-8' \
     -d $'{ "url": "https://example.com/test.mp3" }'

# sample result:

{
  "full_text":"Sample transcription",
  "segments":[{"id":0,"seek":0,"start":0.0,"end":3.74,"text":"Sample transcription"}],
  "model":"base.en"
}