Contribution is the leg where the broadcaster is still in control of both ends of the link. The signal might come from a stadium to a teleport via SDI, from a remote contributor's laptop to a cloud encoder over the public internet, or from a field reporter's bonded-cellular bag to a media gateway. The goal is to land a clean, high-quality feed at the encoder with bounded latency and bounded loss. Cost per stream is high — you might pay for satellite time or for a four-modem bonded link — but the number of streams is small, often one.
The standard contribution protocols are SRT, RIST, Zixi and (legacy) RTMP. WebRTC and WHIP have joined the list for browser- and software-source contribution. SDI and SMPTE ST 2110 remain the standards inside a broadcast facility. Each picks a different tradeoff between latency, packet recovery and ease of NAT traversal. RTMP is still common because of OBS support but is being phased out in favour of SRT for newer deployments.
Contribution is opposite-shaped to distribution. Distribution serves millions of viewers from few origins via a CDN; contribution feeds one origin from one or a handful of sources. The same encoder vendor often sells both ends of contribution (the field unit and the receiver in the data centre), and the design pattern is paired rather than scaled.
