Video.Taxi gives you the option to use videos stored in your media library as a livestream source:
In order to use a video on demand (VOD) as a livestream source, the video must be stored in your media library as a VOD first. Do you need help uploading VODs? You do not know which video formats are allowed? The linked articles will help you.
The video you want to stream is already in your media library? Then create a livestream and select "Premiere a VOD" as the input source in step 1. A new drop-down field will automatically open in which you can select the desired video. If you are not familiar with setting up livestreams yet, this article in the Help Centre will help you.