Online video services account for a major part of broadband traffic with streaming videos being one of the most popular video services. We focus on the user perceived quality of
YouTube videos as it can serve as a general index for customer satisfaction. Our tool, Pytomo , is a tomography tool that is designed to measure the playback quality of videos as if it is being viewed by a user. We model the YouTube video player to estimate the playback interruptions as experienced by a user watching a YouTube video.We also examine topology and download statistics such as delay towards the server, download rates, and buffering duration. We aim to analyse different DNS resolvers to obtain the IP
address of the video server. We study how the DNS resolution impacts the performance of the video download, thus the video playback quality. As the tool is intended to run on multiple ISPs, we have discovered some interesting results in YouTube distribution policies. These results can be applied to any contentdelivery networks (CDN) architecture and should help users to better understand what are the key performance factors of video streaming.