I can’t hear the audio of the recorded videos.
Please check that the silent mode is turned off for your iPhone as in the silent mode the audio of the videos have been disabled. If you are using headsets, you should be able to hear the audio regardless of the silent mode turned on.
All iPhones and some iPads have a ring/silent switch on the left side of the device above the volume buttons. To turn the silent mode off, move the switch towards you so that the orange color isn’t showing. Pushing the switch away from you will turn the silent mode on.