By way of a reminder: it is almost always unlawful to record audio in commercial properties or public places. For why this is the case - you can check here.
However, if you have made up your mind that you need to have audio for your residential CCTV system and got both a camera and NVR that support audio recordings - then this is a short post on how to get it activated.
>Before you Start
Make sure that your camera supports audio function. A quick note about this is here.
If the camera does not have a built-in mic, then get an in-line external active microphone.
Download and install Hikvision client software: iVMS-4200 & iVMS-450
>Enable audio on the camera
Step 1 - Log-into your camera
Step 2 - Go to Configuration
Step 3 - Click Video/Audio and set the video type to Video&Audio
Step 4 - Go to Audio tab to set audio input to LineIn.
> Enable audio on the Live View Page
Step 1 - Go to Live View tab
Step 2 - Enable the audio output by clicking the audio icon and adjust its volume.
> Enable Audio on NVR
Step 1 - Log-into your NVR
Step 2 - Make sure that video footage is recorded on the NVR . Some guidance on this can be found here.
Step 3 - In the Playback tab - click enable audio icon.