Server-Sent Events

Server-Sent Events (SSE) is a way for a server to trickle out updates as work happens, piece by piece. It's like a food delivery app showing order received, cooking, out for delivery, and arrived, one after another. Instead of asking once and waiting for a single answer, the client keeps a connection open while the server pushes progress updates on its own.

When AI generates video or images, finishing can take anywhere from tens of seconds to several minutes. If nothing happens on screen during that time, users can't tell whether it's an error or just still working. With Server-Sent Events, the server can keep sending signals like waiting, processing, or percent complete, so the screen can show a live progress indicator.

That said, this method is built for one-way messaging from server to client. If a conversation needs to be two-way, with the client continuously sending things to the server as well, other approaches may fit better.

The article cites "real-time SSE progress updates" as one of Hedra's strengths. A common misunderstanding here is that SSE doesn't mean the output itself is generated in real time. In reality, it's just a communication method where the server keeps reporting what stage a long-running task like video generation is currently in—waiting, processing, complete, or failed—so developers can use it to show users real-time progress or status.