Why does streaming sometimes lag behind live TV?

When you're watching the live stream of something like a football match, sometimes the live stream lags a few seconds behind the feed on the radio or linear TV. Why does this occur? The reason lies in the multiple stages required to transition a live broadcast to streaming apps.

One of the major advantages of streaming video is the ability to watch significant events while on the go. However, when you compare a live stream with the same event being broadcast on traditional TV, you'll notice a downside: the streamed video often lags behind the live broadcast, sometimes by up to 30 seconds.

So, why does this happen? It's due to the complex process of converting a live broadcast into a streamable format.

Video Capture

The camera captures the image, which is typically sent to an outside broadcast van before being transmitted via satellite or a dedicated landline to the broadcast centre.

Encoding

The video feed is incredibly data-heavy and requires compression using a codec. This compression process reduces gigabytes of data to more manageable megabytes. Simultaneously, the video is transcoded into various file formats to cater to different internet speeds, with each stream potentially having up to 10 different bitrate profiles.

Packaging

Next, the compressed video needs to be packaged for delivery, which involves adding a file container format and implementing digital rights management (DRM) security protocols.

Delivery

The video must then be delivered from the source to the viewer. The further the viewer is from the media server, the longer the video takes to arrive, potentially leading to latency and buffering. To mitigate these issues, Content Distribution Networks (CDNs) are used. These networks consist of servers spread across the country to distribute the load and ensure the video is streamed from the closest possible point to the viewer.

Playback

The video stream on the user's device is broken into short segments, each a few seconds long. The device constantly monitors the quality and speed of its internet connection and communicates this back to the source. If the connection is strong, higher bitrate segments are sent, resulting in a clearer picture. If the connection weakens, lower bitrate segments are sent, which may cause the video to become pixelated. Despite this, the user experiences smooth playback overall.

All of these processes happen in real-time as the event unfolds, presenting a significant challenge for live-streaming companies as it inevitably causes a delay compared to live broadcasts. However, ongoing advancements aim to speed up these processes, and we can expect this lag to decrease over time.