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Enable OpenVINO™ Optimization for WeNet

February 8, 2023


The WeNet model provides two-pass approach to unify streaming and non-streaming end-to-end (E2E) speech recognition which is widely used with various HW platforms. In this blog, we provide the OpenVINO™ optimization for WeNet on Intel® platforms.

The public WeNet project is referenced from: wenet-e2e/wenet

The WeNet model can be considered as a pipeline which is split into 3 parts for decoder, CTC and encoder. Refer the model structure in below picture:

WeNet model processing flow

We implement the wrapper function of Automatic Speech Recognition (ASR) model class with OpenVINO™ runtime API programming for these 3 models’ data preparation and inference. Please refer the integrated OpenVINO™ optimization in official project: wenet-e2e/wenet/runtime/openvino

OpenVINO™backend on WeNet

In this project, you do not require to download OpenVINO™ and build the library with WeNet project manually. It’s already fully integrated with OpenVINO™ runtime library for downloading, program compiling and linking. If your operating system is not one of OpenVINO™ runtime library supported, the script will download OpenVINO™ source from Github, and build with CPU plugin to support.

At present, this repository already optimized and validated by OpenVINO™ 2022.3.0 version. Check the operating system which can support OpenVINO™ runtime library directly:

  • Windows* 10
  • CentOS 7, Red Hat* Enterprise Linux* 8
  • Ubuntu* 18.04, 20.04
  • Debian 9.13 for X86
  • macOS* 10.15
git clone
cd wenet

Step 1: Get pretrained ONNX model (Optional)

If you already have the exported ONNX model for WeNet test, you can skip this step.

For users to get pretrained model from WeNet project, you can refer this link:

Export to 3 ONNX models, including encoder.onnx, ctc.onnx and decoder.onnx by export_onnx_cpu script.

python -m wenet.bin.export_onnx_cpu \
  --config ${model_path}/train.yaml \
  --checkpoint ${model_path}/ \
  --chunk_size 16 \
  --output_dir ${onnx_dir}\
  --num_decoding_left_chunks -1

Step 2: Convert ONNX model to OpenVINO™ Intermediate Representation (IR)

Make sure your python environment already installed OpenVINO™ runtime library.

pip install openvino

Convert these three ONNX models into IR by OpenVINO™ Model Optimizer command:

mo --input_model ${onnx_dir}/encoder.onnx --input chunk,att_cache,cnn_cache --input_shape [1,-1,80],[12,4,-1,128],[12,1,256,7] --output_dir ${openvino_dir} 
mo --input_model ${onnx_dir}/ctc.onnx --input_shape [1,-1,256] --output_dir ${openvino_dir}
mo --input_model ${onnx_dir}/decoder.onnx --input hyps,hyps_lens,encoder_out --input_shape [-1,-1],[-1],[1,-1,256] --output_dir ${openvino_dir}

Step 3: Build WeNet with OpenVINO™ backend

Please refer system requirement to check if the hardware platform available by OpenVINO™. It will download and install OpenVINO™ library during the CMake configuration.

cd ./runtime/openvino
mkdir build && cd build
make --jobs=$(nproc --all)

Some users may cannot easily download OpenVINO™ binary package from server due to firewall or proxy issue. If you failed to download by CMake script, you can download OpenVINO™ package by your selves and put the package to below path:


If you already have OpenVINO™ runtime which is manually built before the WeNet building, you can put the runtime library to below path:


Step 4: Simple inference test

You may run the inference test like below with the speech input audio file (.wav) and model unit file (.txt):

./bin/decoder_main \
    --chunk_size 16 \
    --wav_path ${wav_path} \
    --openvino_dir ${openvino_dir} \
    --unit_path ${unit_path}

The information of OpenVINO™ integration and results will be print out:

    Version : 2022.3.0
    Build   : 2022.3.0-9052-9752fafe8eb-releases/2022/3

Get Encoder input chunk
Get Encoder input offset
Get Encoder input att_cache
Get Encoder input cnn_cache
test 如果你尝试了就会知道这是个很有趣的例子

Extend OpenVINO™ to run PyTorch models with custom operations

February 1, 2023

Authors: Anna Likholat, Nico Galoppo

The OpenVINO™ Frontend Extension API lets you register new custom operations to support models with operations that OpenVINO™ does not support out-of-the-box. This article explains how to export the custom operation to ONNX, add support for it in OpenVINO™, and infer it with the OpenVINO™ Runtime.

The full implementation of the examples in this article can be found on GitHub in the openvino_contrib.

Export a PyTorch model to ONNX

Let's imagine that we have a PyTorch model which includes a new complex multiplication operation created by user (this operation was taken from DIRECT):

def complex_multiplication(input_tensor: torch.Tensor, other_tensor: torch.Tensor) -> torch.Tensor:
    assert_complex(input_tensor, complex_last=True)
    assert_complex(other_tensor, complex_last=True)
    complex_index = -1
    real_part = input_tensor[..., 0] * other_tensor[..., 0] - input_tensor[..., 1] * other_tensor[..., 1]
    imaginary_part = input_tensor[..., 0] * other_tensor[..., 1] + input_tensor[..., 1] * other_tensor[..., 0]
    multiplication =
    return multiplication

class MyModel(nn.Module):
    def __init__(self):
      super(MyModel, self).__init__()

    def forward(self, x, y):
      return complex_multiplication(x, y)

We'd like to export the model to ONNX and preserve complex multiplication operations as single fused nodes in the ONNX model graph, so that we can replace those nodes with custom OpenVINO operations down the line. If we were to export MyModel which directly calls the function above from its forward method, then onnx.export() would inline the PyTorch operations into the graph. This can be observed in the figure of the exported ONNX model below.

To prevent inlining of native PyTorch functions during ONNX export, we can wrap the function in a sub-class of torch.autograd.Function and define a static symbolic method. This method should return ONNX operators that represent the function's behavior in ONNX. For example:

class ComplexMul(torch.autograd.Function):
    def symbolic(g, input_tensor, other_tensor, is_conj = True):
      return g.op("ComplexMultiplication", input_tensor, other_tensor, is_conj_i=int(is_conj))

    def forward(ctx, input_tensor, other_tensor):
      return complex_multiplication(input_tensor, other_tensor)

class MyModel(nn.Module):
    def __init__(self):
      super(MyModel, self).__init__()
      self.complex_mul = ComplexMul()

    def forward(self, x, y):
      return self.complex_mul.apply(x, y)

You can find the full implementation of the wrapper class here:

So now we're able to export the model with custom operation nodes to ONNX representation. You can reproduce this step with the script:

cd modules/custom_operations
python -m examples.complex_mul.export_model

The resulting ONNX model graph now has a single ComplexMultiplication node, as illustrated below:

Enable custom operation for OpenVINO with Extensibility Mechanism

Now we can proceed with adding support for the ComplexMultiplication operation in OpenVINO. We will create an extension library with the custom operation for OpenVINO. As described in the Custom OpenVINO Operations docs, we start by deriving a custom operation class from the ov::op::Op base class, as in complex_mul.hpp.

1. Implement Operation Constructors

Implement the default constructor and constructors that optionally take the operation inputs and attributes as parameters. (code)

2. Override methods

2.1 validate_and_infer_types() method

Validates operation attributes and calculates output shapes using attributes of the operation: complex_mul.cpp.

2.2 clone_with_new_inputs() method

Creates a copy of the operation with new inputs: complex_mul.cpp.

2.3 has_evaluate() method

Defines the contstraints for evaluation of this operation: complex_mul.cpp.

2.4 evaluate() method

Implementation of the custom operation: complex_mul.cpp

3. Create an entry point

Create an entry point for the extension library with the OPENVINO_CREATE_EXTENSIONS() macro, the declaration of an extension class might look like the following:


        // Register operation itself, required to be read from IR

        // Register operaton mapping, required when converted from framework model format

This is implemented for the ComplexMultiplication operation in ov_extension.cpp.

4. Configure the build

Configure the build of your extension library using CMake. Here you can find the template of such script:

set(TARGET_NAME "complex_mul_extension")

find_package(OpenVINO REQUIRED)

set(SRC complex_mul.cpp ov_extension.cpp)

add_library(${TARGET_NAME} MODULE ${SRC})

target_link_libraries(${TARGET_NAME} PRIVATE openvino::runtime)

Also see an example of the finished CMake script for module with custom extensions here: CMakeLists.txt.

5. Build the extension library

Next we build the extension library using CMake. As a result, you'll get a dynamic library - on Linux it will be called, after the TARGET_NAME defined in the CMakeLists.txt above.

cd user_ie_extensions
mkdir build && cd build
cmake .. -DCMAKE_BUILD_TYPE=Release && cmake --build . --parallel 4

Deploy and run the custom model

You can deploy and run the exported ONNX model with custom operations directly with the OpenVINO Python API. Before we load the model, we load the extension library into the OpenVINO Runtime using the add_extension() method.

from openvino.runtime import Core
core = Core()

# Load extension library

Now you're ready to load the ONNX model, and infer with it. You could load the model from the ONNX file directly using the read_model() method:


Alternatively, you can convert to an OpenVINO IR model first using Model Optimizer, while pointing at the extension library:

mo --input_model model.onnx --extension /path/to/

Note that in this case, you still need to load the extension library with the add_extension() method prior to loading the IR into your Python application.

The complete sequence of exporting, inferring, and testing the OpenVINO output against the PyTorch output can be found in the custom_ops test code.

See Also


Remote Tensor API Sample

January 28, 2023

This AI pipeline implements zero-copy between SYCL and OpenVINO through the Remote Tensor API of the GPU Plugin.

  1. Introduction

The development of SYCL simplifies the use of OpenCL, which can fully exploit the computing power of GPU in the pipeline. Meanwhile, SYCL has more flexibility to do customized pre- and post-processing of OpenVINO. To further optimize the pipeline, developers can use GPU Plugin to avoid the memory copy overhead between SYCL and OpenVINO. The GPU plugin provides the ov::RemoteContext and ov::RemoteTensor interfaces for video memory sharing and interoperability with existing native APIs, such as OpenCL, Microsoft DirectX, or VAAPI. For details, please refer to the online documentation of OpenVINO.

Based on the pseudocode of the online documentation, here we provide a simple pipeline sample with Remote Tensor API. Because in the rapid iteration of oneAPI, sometimes customers need quick verification so that this sample can be used for testing. OneAPI also provides a real-world, end-to-end example, which optimizes PointPillars for lidar object detection.

  1. Components

SYCL preprocessing is based on the Sepia Filter sample, which demonstrates how to convert a color image to a Sepia tone image, a monochromatic image with a distinctive Brown Gray color. The sample program works by offloading the compute-intensive conversion of each pixel to Sepia tone using SYCL*-compliant code for CPU and GPU.

OpenVINO inferencing is based on the OpenVINO classification sample, the input from SYCL filtered image in the device will be sent into OpenVINO as a remote tensor without a memory copy.

Remote Tensor API: Create RemoteContext from SYCL pre-processing’s native handle. After model compiling, do memory sharing between the application and GPU plugin with from cl::Buffer to remote tensor.

auto cl_queue = get_native<backend::opencl>(sycl_queue);
auto remote_context = ov::intel_gpu::ocl::ClContext(core, cl_queue);
ov::CompiledModel compiled_model = core.compile_model(model, remote_context);
auto cl_buffers = get_native<backend::opencl>(image_buf_out);
auto remote_tensor = remote_context.create_tensor(ov::element::u8, {batch, input_height, input_width, 3}, cl_buffers);
infer_request.set_tensor(input_tensor_name, remote_tensor);
  1. Build Sample on Linux

Download the source code from sandbox. Prepare the model and images.

To run the sample, you need to specify a model and image:

Use pre-trained models from the Open Model Zoo. The models can be downloaded using the Model Downloader. Use images from the media files collection.

mkdir build
cd build
cmake ..

Run on Intel NUC Core 11 iGPU with OpenVINO 2022.2 and oneAPI 2022.3.

./intel64/hello_nv12_input_classification_oneAPI../model/FP32/alexnet.xml ../image/dog512.bmp GPU 2

Sample Output:

  Loaded image with a width of 512, a height of 512 and 3 channels
[ INFO ] OpenVINO Runtime version ......... 2022.2.0
[ INFO ] Build ........... 2022.2.0-7713-af16ea1d79a-releases/2022/2
[ INFO ] 
[ INFO ] Loading model files: ../model/FP32/alexnet.xml
Running on Intel(R) Iris(R) Xe Graphics [0x9a49]
---Load model - 1126ms
---Create an infer request - 0.515ms
Use remote tensor API and set_tensor
No 1. do inf: 
---sycl buffer  - 0.005ms
---sycl filter total time - 93.342ms
---kernel time: 0.051822 milliseconds
---Set tensor - 0.138ms
---Run infer req - 4.725ms
---get tensor - 0.062ms

Top 3 results:

Image ../image/dog512.bmp

classid probability label
------- ----------- -----
176     0.4579958   "Saluki, gazelle hound"
212     0.2727944   "English setter"
169     0.0513433   "borzoi, Russian wolfhound"

---sum of inference - 98.268ms
No 2. do inf: 
---sycl buffer  - 0.001ms
---sycl filter total time - 0.582ms
---kernel time: 0.05177 milliseconds
---Set tensor - 0.086ms
---Run infer req - 4.162ms
---get tensor - 0.049ms

Top 3 results:

Image ../image/dog512.bmp

classid probability label
------- ----------- -----
176     0.4579958   "Saluki, gazelle hound"
212     0.2727944   "English setter"
169     0.0513433   "borzoi, Russian wolfhound"

---sum of inference - 4.881ms 

Warning: With the updating of OpenVINO and oneAPI, different versions may cause problems with the tools in the common directory or the new SYCL header name. Please use the same version or debug following the corresponding release instructions.


Serving OpenVINO Models using the KServe API Standard

There are many network API specifications for model serving on the market today. Two of the most popular are TensorFlow Serving (TFS) and KServe. Starting with the 2022.2 release, OpenVINO Model Server supports KServe -- meaning both of these common API standards can be used for serving OpenVINO models. This blog explains how to take advantage of either API.

OpenVINO provides an efficient and high-performance runtime for executing deep learning inference. In many situations, AI applications need to delegate inference execution to a remote device or service over a network. There are many advantages to this approach including the ability to scale.

Figure 1. Example of a client sending image input to a model server for image classification.

AI software developers expect the communication interface with a model server to remain stable. In many cases, developers want to perform pre/post-processing on the client side with minimal dependencies. They are reluctant to switch to a different serving implementation if that requires substantial code changes or new dependencies in their applications.

Since the first release in 2018, OpenVINO Model Server has supported the TFS API. And as of 2022, the KServe API is now supported as well.

KServe is a standard designed by several companies across the industry. It has been adopted by model servers like Triton Inference Server and TorchServe. Now the same client can easily switch to use OpenVINO Model Server and leverage the latest optimizations in Intel(R) CPUs and GPUs.

KServe Python Example

Below is a simple example how to use KServe using the Python-based tritonclient.

Create Model Repository

wget{xml,bin} -P models/resnet/1
tree models
	└── resnet
		└── 1        

Start OpenVINO Model Server with a ResNet-50 Model:

docker run --rm -d -v $(pwd)/models:/models -p 9000:9000 -p 8000:8000 openvino/model_server:latest --model_name resnet --model_path /models/resnet --port 9000 --rest_port 8000 --layout NHWC:NCHW --plugin_config '{"PERFORMANCE_HINT":"LATENCY"}'

Install Python Client Library

pip install tritonclient[grpc]==2.22.3

Get the Model Metadata

import tritonclient.grpc as grpcclientclient = grpcclient.InferenceServerClient("localhost:9000")print(client.get_model_metadata("resnet"))

Get a Sample Image


JPEG image of a bee

Run Inference via gRPC Interface with a NumPy File as Input Data

pip install opencv-python
import tritonclient.grpc as grpcclient
import cv2
import numpy as np
img = cv2.imread("bee.jpeg").astype(np.float32)
img = cv2.resize(img, (224, 224))
img = img.reshape(1,224,224,3)
triton_client = grpcclient.InferenceServerClient("localhost:9000")
inputs =[grpcclient.InferInput("0", img.shape, "FP32")]
results = triton_client.infer(model_name="resnet", inputs=inputs)
probabilities = results.as_numpy('1463')

Run Inference via REST Interface with a JPEG File as Input Data

pip install requests
import requests
import json
import numpy as np

image = open("bee.jpeg", 'rb')
image_data = []

http_session = requests.session()
inference_header = {"inputs":[{"name":"0","shape":[1],"datatype":"BYTES"}]}
inference_header_binary = json.dumps(inference_header).encode()
results ="http://localhost:8000/v2/models/resnet/versions/0/infer", inference_header_binary + b''.join(image_data), headers={"Inference-Header-Content-Length":str(len(inference_header_binary))})
probabilities = np.array(json.loads(results.text)['outputs'][0]['data'])


Run Inference via REST Interface with a JPEG File as Input Data using cURL

echo -n '{"inputs" : [{"name" : "0", "shape" : [1], "datatype" : "BYTES"}]}' > request.json
stat --format=%s request.json
cat ./bee.jpeg >> request.json
curl --data-binary "@./request.json" -X POST http://localhost:8000/v2/models/resnet/versions/0/infer -H "Inference-Header-Content-Length: 66"

KServe C++ Example

The inference execution is also made easy in C++ based client applications. The examples below show client application execution based on the Triton C++ client library.

Build the Samples:

git clone –b develop
cd model_server/client/cpp/kserve-api 
cmake . && make && cd samples


Get the Model Metadata

The compiled application grpc_model_metadata can make a call to gRPC endpoint and query for a server model metadata.

./grpc_model_metadata --grpc_port 9000 --grpc_address localhost --model_name resnet
model metadata:
name: "resnet"
versions: "1"
platform: "OpenVINO"
inputs {
  name: "0"
  datatype: "FP32"
  shape: 1
  shape: 224
  shape: 224
  shape: 3
outputs {
  name: "1463"
  datatype: "FP32"
  shape: 1
  shape: 1000

Run Inference via gRPC with a JPEG Encoded File as the Input Data

The sample application grpc_infer_resnet is sending the inference requests for a set of images listed inresnet_input_images.txt including their expected classification number in the ImageNet dataset.

./grpc_infer_resnet --images_list resnet_input_images.txt --labels_list resnet_labels.txt --grpc_port 9000  

airliner.jpeg classified as 404 airliner 
arctic-fox.jpeg classified as 279 Arctic fox, white fox, Alopex lagopus 
bee.jpeg classified as 309 bee 
golden_retriever.jpeg classified as 207 golden retriever 
gorilla.jpeg classified as 366 gorilla, Gorilla gorilla 
magnetic_compass.jpeg classified as 635 magnetic compass 
peacock.jpeg classified as 84 peacock 
pelican.jpeg classified as 144 pelican 
snail.jpeg classified as 113 snail 
zebra.jpeg classified as 340 zebra 
Accuracy 100%

======Client Statistics======
Completed request count 10
Cumulative total request time 110.314 ms

In addition to the KServe API, the TFS API can still be used by client applications. This gives you the option to use a range of client libraries like tensorflow-serving-api or the much lighter and simplified ovmsclient.

To help you get started, we provide samples in Python, C++, Java and Go:

In conclusion, it is now easier to connect and AI applications to OpenVINO Model Server. In existing applications, you can even use the same code to take advantage of the benefits of OpenVINO.