Walmart is buying the smart TV maker Vizio for $2.3 billion as it attempts to expand its rapidly growing advertising business to compete with Amazon. If completed, the deal would give Walmart access to Vizio’s SmartCast operating system, allowing the retail behemoth to offer its suppliers the ability to display ads on streaming devices. Walmart has been ramping up its media and ad business with Walmart Connect, giving advertisers access to Walmart’s massive customer base.