I'm wondering how those popular media rich websites implement their media library. Do they store all the media files in the database? What kind of database do they use? Do they employ other mechanism to boost the performance?
Thanks for any response.
You are asking a very difficult question to answer.
I recommend that as an introductory read you check out Youtube Architecture on High Scalability. Youtube is a very good real-life example of how a media-centric website works.
Surprising as it may be, serving the actual media files is not the bottleneck. The harder part is getting all the media meta-data synched, generating thumbnails, etc. Media files can always be hosted from a cluster, or from a CDN in case of an extremely popular video.
Read the link for more in-depth info.
"Popular Media Sites" is pretty broad, but typically high volume rich media sites use Content Delivery Networks, such as Akamai, etc or cloud based storage like AmazonS3
Speaking as a dev on a popular media website, we offload the serving of video to 3rd parties (YouTube and BrightCove). Depending on the situation, we then host this video within a custom player to layer in ads and other features. Pumping down video streams is best handled by someone else who has invested a lot of energy and money into their architecture.
As with everything, you need to decide if you needs are specific enough to warrant developing in-house vs effort of integrating with other tools.