I do not claim that silent video in general is better than video with texts. Different types of videos (with/without sound/text) are good for different purposes. For this purpose, where teachers want to gather students' ideas on certain mathematical topics in a broad sense and students are expected to add their own description/explanation/narrative to the video, it is necessary to have the video without any sound or text. The reason being, that the text/sound otherwise would direct students into certain paths in their responses, channeling their ideas and thus limiting their creativity.

Each has its own advantages

Thank you!