Thank you for the great question. With VOD, we have a couple of different ways you could scale and support that number of viewers. We would recommend:
Media Cache is a read-through caching mechanism built-in with Wowza Streaming Engine media server software that increases the scalability of video-on-demand (VOD) streaming.
B. Scale with a CDN
If you have Wowza Streaming Engine and use a CDN then you can configure a VOD HTTP Origin application on your Wowza Streaming Engine and have your CDN connect to it. Your CDN will cache your VOD content. We have an article that covers this below.
For more scaling options, go HERE.