Design the ingest-and-transcode backbone for a live-streaming product. A broadcaster pushes a single high-bitrate source over RTMP or SRT; your system must turn that one feed into a ladder of lower-bitrate renditions and publish playable segments to viewers with only a few seconds of delay.

Operating context. Broadcasters range from a phone in a stadium to a professional encoder. Each source arrives at up to 12 Mbps and must be re-encoded in real time into several renditions (roughly 1080p down to 360p), segmented, and packaged for delivery. The transcode fleet is CPU/GPU-bound and must scale with the number of concurrent live streams. A worker can crash mid-broadcast, and viewers must not see the stream stall for more than a moment.

Out of scope. Player-side rendition selection and buffering logic, DRM and content encryption, permanent VOD archival of the broadcast, live chat and reactions, and the CDN's internal caching design. Assume separate teams own those.

What to produce. A high-level architecture covering: the ingest path and stream-key validation, how a single source is fanned out into a parallel rendition ladder, segmentation and packaging into HLS/DASH chunks, the origin and hand-off to the CDN, how the transcode fleet autoscales while staying real-time, and how an in-flight stream recovers when a worker dies. Sketch the components and the flow of one stream through them; we will probe specifics during checkpoints.