1. The specific parameters of the product can be viewed by clicking on the preview and then clicking the [Click to view video parameters] button below. Whether the video has sound is subject to the preview video. Our customer service will not answer questions about product parameters. 2. Because the products are reproducible, no refunds are given once purchased. Please be sure to preview the products before considering whether to purchase. 3. All materials can only be used for learning purposes. This store does not have tutorials. Please do not add customer service to request tutorials. 4. If you have any system function problems, you can add customer service in the [Help] below. Please indicate your purpose when adding.