Why is there no sound in the videos recorded by the Xiaomi Outdoor Camera CW300?

All the videos recorded in these recording forms have sound. However, if double-speed playback is enabled, it will be played silently by default.
In addition, every time you enter the camera monitoring interface or the interface of the cloud storage and the memory card storage, the video is played silently by default. You can tap the mute button to play the sound normally.