To make it more clear, this broadcaster is not someone speaking over a microphone, it's just someone using their cellphone to broadcast a live session to viewers. Ideas?
A broadcaster is generally someone, or something, that distributes, relays, transmits a message to someone, or something, else.
The translation provided by Google Translator for "broadcaster" is "locutor de rádio", which is a very specific type of broadcasting, for radio.
However, you can find more meaningful translations for "broadcast" such as "transmissão" (transmission, to transmit) or "difundir" (to propagate).
So the broadcaster is the "transmissor" or "emissor" as @Jacinto suggested.
Both "broadcast" and "broadcasting" can also be used as foreign words, they are even accepted without the use of quotation marks. This usually happens when foreign words are adopted as is to another language, due to relatively high usage.
I would use "divulgador". The verb "divulgar" means to spread information or ideas to a large public, in any form, verbal, written or visual. "Difundir" can also be used, but the derivated noun "difusor" can be confused with something that difuses a substance in another one. "Divulgador" leaves no doubt.