# ECP-0042: Multi-Variant Publishing and Automatic Selection

## Why

Different networks and devices need different bitrates/resolutions. A single stream quality forces either wasted bandwidth or playback stalls. We also need a consistent representation of variants so multiple peers can publish/verify the same logical channel.

## Decisions

- A "channel" may have multiple *variants* (e.g. `1080p`, `720p`, `480p`) produced from the same timing grid.
- Manifests include per-variant metadata (resolution/bitrate) and per-variant chunk hashes for the same chunk index.
- Viewers implement automatic selection:
  - Prefer the highest variant that keeps steady playback.
  - Step down quickly on sustained stalls; step up conservatively.
- Where available, the desktop app may present variants via a master playlist so the platform player can do ABR; protocol objects remain per-variant CMAF.
  - Initial implementation may subscribe to all variants concurrently and let the player switch locally. More efficient "switch by resubscribe" can come later.

## Non-Goals (for this ECP)

- Global policy/quotas/anti-junk (separate proposal).
- Hardware encode determinism guarantees (separate proposal).

## Reversibility

High. Variant publishing and selection policies can evolve without breaking base single-variant streams.