Speech Recognition Demo

This demo demonstrates Automatic Speech Recognition (ASR) with a pretrained Mozilla* DeepSpeech 0.8.2 model.

It works with version 0.6.1 as well, and should also work with other models trained with Mozilla DeepSpeech 0.6.x/0.7.x/0.8.x with ASCII alphabets.

How It Works

The application accepts

  • Mozilla* DeepSpeech 0.8.2 neural network in Intermediate Representation (IR) format,
  • n-gram language model file in kenlm quantized binary format, and
  • an audio file in PCM WAV 16 kHz mono format.

After computing audio features, running a neural network to get per-frame character probabilities, and CTC decoding, the demo prints the decoded text together with the timings of the processing stages.


The demo depends on the ctcdecode_numpy Python extension module, which implements CTC decoding in C++ for faster decoding. Please refer to Open Model Zoo demos for instructions on how to build the extension module and prepare the environment for running the demo. Alternatively, instead of using cmake you can run python -m pip install . inside ctcdecode-numpy directory to build and install ctcdecode-numpy.

Model preparation

You can download and convert a pre-trained Mozilla* DeepSpeech 0.8.2 or 0.6.1 model with OpenVINO Model Downloader and the provided conversion scripts. This is done with the following commands:

source <openvino_dir>/bin/setupvars.sh
<openvino_dir>/deployment_tools/open_model_zoo/tools/downloader/downloader.py --name mozilla-deepspeech-0.8.2
<openvino_dir>/deployment_tools/open_model_zoo/tools/downloader/converter.py --name mozilla-deepspeech-0.8.2


source <openvino_dir>/bin/setupvars.sh
<openvino_dir>/deployment_tools/open_model_zoo/tools/downloader/downloader.py --name mozilla-deepspeech-0.6.1
<openvino_dir>/deployment_tools/open_model_zoo/tools/downloader/converter.py --name mozilla-deepspeech-0.6.1

Please pay attention to the model license, Mozilla Public License 2.0.

Running Demo

Run the application with -h option to see help message. Here are the available command line options:

usage: speech_recognition_demo.py [-h] -i FILENAME [-d DEVICE] -m FILENAME
[-L FILENAME] -p NAME [-b N] [-c N]
Speech recognition demo
optional arguments:
-h, --help show this help message and exit
Path to an audio file in WAV PCM 16 kHz mono format
-d DEVICE, --device DEVICE
Optional. Specify the target device to infer on, for
sample will look for a suitable IE plugin for this
device. (default is CPU)
Path to an .xml file with a trained model (required)
path to language model file (optional)
-p NAME, --profile NAME
Choose pre/post-processing profile: mds06x_en for
Mozilla DeepSpeech v0.6.x, mds07x_en or mds08x_en for
Mozilla DeepSpeech v0.7.x/x0.8.x, other: filename of a
YAML file (required)
-b N, --beam-width N Beam width for beam search in CTC decoder (default
-c N, --max-candidates N
Show top N (or less) candidates (default 1)
-l FILENAME, --cpu_extension FILENAME
Optional. Required for CPU custom layers. MKLDNN
(CPU)-targeted custom layers. Absolute path to a
shared library with the kernels implementations.

The typical command line is:

pip install -r requirements.txt
source <openvino_dir>/bin/setupvars.sh
python speech_recognition_demo.py \
-p mds08x_en \
-m <ir_dir>/FP32/mozilla_deepspeech_0.8.2.xml \
-L <path_to_tf_model>/deepspeech-0.8.2-models.kenlm \
-i <path_to_audio>/audio.wav

For version 0.6.1 it is:

python speech_recognition_demo.py \
-p mds06x_en \
-m <ir_dir>/FP32/mozilla_deepspeech_0.6.1.xml \
-L <path_to_tf_model>/lm.binary \
-i <path_to_audio>/audio.wav

Only 16-bit, 16 kHz, mono-channel WAVE audio files are supported.

An example audio file can be taken from <openvino_dir>/deployment_tools/demo/how_are_you_doing.wav.

Demo Output

The application shows time taken by the initialization and processing stages, and the decoded text for the audio file.