Once the camera makes video signals, it passes them to circuits that control the brightness, contrast, color, and other aspects of the picture. A sample of this signal is sent to your viewfinder, a tiny TV monitor in your camcorder. The audio signals are automatically adjusted so that the volume doesn't get too high or too low. A sample may be sent to your earphone output. A TV monitor or VCR doesn't care whether these signals are coming from a camera and microphone, camcorder, VCR, or from a TV tuner.
Video is video.
Audio is audio. When you pass standard audio and video signals from one machine to another, you can do things with them. Audio can be faded up or down in volume, mixed with music, sound effects, narration, and sweetened in numerous ways. The VCR makes heads spin - Inside your camcorder is a miniature videocassette recorder. It records audio, maybe with high fidelity, and records video.