I emailed them and received this response:


For the 2018 season we are happy to announce that we have launched a brand new, full definition 60 frames per second HTML player.

Adobe flash is no longer required to view MLB.TV. Due to this and other improvements, previous season archives are not available currently in the MLB.TV Media Player.

On-demand 2018 video archives will continue to be available. We are working to add 2017 content to the product offering. Please check back for updates.