Hello zen xu
The copyright question about the generated voice files depends on the terms of service (TOS) of Microsoft TTS. According to the TOS, you retain copyright and any other rights you already hold in Content which you submit, post or display on or through, the Services. As such any sound recordings would be copyrightable at Copyrightgov in the name of the application user.
However, there are some restrictions on how you can use the generated voice files. For example, you cannot use the voice files for commercial purposes without a license from Microsoft.
If you are planning to sell the embedded devices, you should contact Microsoft to discuss the copyright question and to obtain a license to use the voice files for commercial purposes.
Here are the steps on how to contact Microsoft about the copyright question:
- Go to the Microsoft website and click on the Support tab.
- Select the Products tab and select Azure Cognitive Services.
- Click on the Contact us button.
- Select the Copyright option from the Subject drop-down list.
- Enter your contact information and a brief description of your question.
- Click on the Submit button.
A Microsoft representative will contact you to discuss your question and to provide you with more information.
I hope this helps! Let me know if you have any other questions.