# ECP-0005: deterministic chunking pipeline

Status: Draft

## Problem

We need a deterministic encoding and chunking pipeline so that identical broadcasts produce identical objects across relays.

## Decision

Adopt a deterministic chunking profile with the following constraints:

- Single-threaded encoding by default.
- Fixed GOP cadence and keyframe placement.
- Bitexact flags enabled wherever possible.
- Fixed chunk duration (default 2 seconds) and stable object naming.

Initial implementation uses ffmpeg CLI piping into the ac-ffmpeg chunker for rapid iteration, while the primary goal is to move to libav bindings for deeper control and determinism validation.

## Alternatives considered

- Multithreaded encoders: rejected because they reduce reproducibility.
- Hardware encoders: deferred because determinism is uncertain.
- HLS segmentation: rejected as the primary format; MoQ objects will be derived directly.

## Rollout / teardown

- Introduce `ec-chopper` with a deterministic profile and ffmpeg-based segmenter.
- Measure determinism with repeated runs.
- Replace the CLI with libav bindings once the control surface is verified.