every.channel: sanitized baseline

evolution/proposals/ECP-0035-multi-variant-streams.md

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+# ECP-0035: Multi-Variant Streams (Quality Pools)
+
+Status: Draft
+Author: Codex
+Reviewers: founder@every.channel
+Created: 2026-02-07
+
+## Decision
+
+Support multiple quality variants per logical channel/stream (bitrate, resolution, codec profile) by:
+
+- Encoding/publishing each variant as its own `StreamId` (using `StreamKey.variant`).
+- Advertising the variant set in the stream catalog so receivers can pick one (or switch).
+- Keeping the transport canonical at CMAF init + fMP4 fragments; playlists (HLS) are optional views.
+
+## Motivation
+
+- Scaling: low-bitrate variants are cheaper to relay and friendlier to mobile.
+- Interop: many origins already provide ABR ladders (HLS/DASH); we should preserve that structure.
+- Determinism experiments: variants bound the encoding parameters so byte-equivalence is testable.
+
+## Scope
+
+In scope:
+- Catalog representation for variants.
+- CLI/UI selection of a variant for playback/subscription.
+- Optional "encode ladder" mode for local sources (HDHR/DVB) using x264 in deterministic settings.
+
+Out of scope:
+- Full ABR switching heuristics.
+- Distributed, consensus-driven variant negotiation.
+
+## Proposed Data Model
+
+Add to `ec-core` (names illustrative):
+
+- `StreamVariant`:
+  - `variant_id` (string, stable, e.g. `v1-1080p2500k`)
+  - `stream_id` (StreamId)
+  - `codec` (e.g. `h264`)
+  - `container` (e.g. `cmaf/fmp4`)
+  - `width/height` (optional)
+  - `bitrate` (optional)
+  - `fps` (optional)
+  - `audio` (optional fields)
+
+Add to `StreamCatalogEntry`:
+
+- `variants: Vec<StreamVariant>` (optional; empty implies single-variant legacy)
+
+## Publishing Strategy
+
+- For live sources (HDHR/DVB): spawn one encoder per variant (separate ffmpeg processes initially).
+- For HLS origins with ABR: map each origin rendition to a variant and (initially) republish bytes as-is when possible.
+
+## Determinism Notes
+
+- Determinism is only expected within the same `variant_id` and encoder profile.
+- Single-threaded x264 settings remain the baseline deterministic profile for now.
+
+## Reversibility
+
+- This is additive to the catalog and backwards compatible (single-variant streams remain valid).
+- Variant publishing can be introduced incrementally per source type.
+