Among the list of Pixel 2 issues uncovered shortly after its launch, was one that resulted in poor audio quality in recorded videos. The problem was officially acknowledged, with Google saying a fix is incoming. And here it is - the fix is included in the latest Android 8.1 developer preview. The following videos clearly show the problem has been taken care of - first one is made with a Pixel 2 unit running Android 8.0 and the next with a phone running Android 8.1 DP2. There are more samples to confirm the issue has been resolved - head to the Reddit and Google Photos links...
Source: https://www.gsmarena.com/google_pixel_2s_issue_with_audio_in_video_recordings_is_fixed_in_android_81_dp2-news-28532.php
