This implementation is about 4 times faster than openai/whisper for the same accuracy while using less memory. The efficiency can be further improved with 8-bit quantization on both CPU and GPU.

Installation

pip install -e .[conversion]

The model conversion requires the modules transformers and torch which are installed by the [conversion] requirement. Once a model is converted, these modules are no longer needed and the installation could be simplified to:

pip install -e .

Usage

Model conversion

A Whisper model should be first converted into the CTranslate2 format. For example the command below converts the "medium" Whisper model and saves the weights in FP16:

ct2-transformers-converter --model openai/whisper-medium --output_dir whisper-medium-ct2 --quantization float16

If needed, models can also be converted from the code. See the conversion API.

Transcription

from faster_whisper import WhisperModel

model_path = "whisper-medium-ct2/"

# Run on GPU with FP16
model = WhisperModel(model_path, device="cuda", compute_type="float16")

# or run on GPU with INT8
# model = WhisperModel(model_path, device="cuda", compute_type="int8_float16")
# or run on CPU with INT8
# model = WhisperModel(model_path, device="cpu", compute_type="int8")

segments, info = model.transcribe("audio.mp3", beam_size=5)

print("Detected language '%s' with probability %f" % (info.language, info.language_probability))

for segment in segments:
    print("[%ds -> %ds] %s" % (segment.start, segment.end, segment.text))

Comparing performance against openai/whisper

If you are comparing the performance against openai/whisper, you should make sure to use the same settings in both frameworks. In particular:

In openai/whisper, model.transcribe uses a beam size of 1 by default. A different beam size will have an important impact on performance so make to use the same.
When running on CPU, make sure to set the same number of threads. Both frameworks will read the environment variable OMP_NUM_THREADS, which can be set when running your script:

OMP_NUM_THREADS=4 python3 my_script.py