While a smart soundbar is usually used to describe a soundbar with an onboard voice assistant, but it can also mean a soundbar that has video streaming capabilities, such as the Roku Streambar. A smart soundbar is often used both as a streaming device and to control other smart home devices via voice. The two assistants that are commonly included with soundbars are Google Assistant and Amazon Alexa.  It's worth noting that adding a separate Google Nest mini or Amazon Echo device to an existing, internet-connected soundbar can often give the same capabilities as a smart soundbar. The added advantage is that it doesn't tie up your soundbar when you ask it a question.