"Poor audio problem in videos."に関する回答Poor audio quality could be a result of a bad microphone. This means you might need to replace the damaged microphone.
"Will the camera save pictures without a memory card installed?"に関する回答The Xiaomi Yi does not have any internal storage. In order to save pictures or videos, you will need to insert a Micro SD card into the back of the device. The Micro SD slot is located above the Micro USB charging port on the back of the device.