# BRIEFING — 2026-10-09T07:45:04Z

## Mission
Investigate and design the technical blueprint for Milestone M4: Scene Concat, Audio Mastering & EBU R128 Architecture (Features F9, F10, F11) across `05_Production_Pipeline/production_orchestrator.py`, `audio_continuity_engine.py`, and `assemble_ep01_feature.py`.

## 🔒 My Identity
- Archetype: explorer
- Roles: [investigation, synthesis]
- Working directory: c:\Projects\KieuStory\.agents\teamwork\explorer_m4_1
- Original parent: f9992164-c0e4-4f7d-ba4a-25a83a4436bf
- Milestone: M4 (Web Review Server & API Endpoints)
- Re-assigned Parent: 97faf5e5-a830-491c-b78c-2af12175badf
- Current Milestone: M4 (Scene Concat, Audio Mastering & EBU R128 Architecture)

## 🔒 Key Constraints
- Read-only investigation — do NOT implement changes in source code
- Only write within `.agents/teamwork/explorer_m4_1`
- Formulate exact code edits, diff patches, or implementation instructions for Worker M4
- Must read ORIGINAL_REQUEST.md and PROJECT.md
- Verify FFmpeg filter_complex syntax preserving 100% AAC 48kHz audio (Zero OpenCV)
- Verify 2-pass loudnorm configuration: I=-14 LUFS, TP=-1.0 dBTP, LRA=9-11 LU, 48kHz stereo AAC
- Design assemble_episode_master("ep01") stitching all 10 scene masters into 06_Exports/ep01_full_feature_master_v1.mp4

## Current Parent
- Conversation ID: 97faf5e5-a830-491c-b78c-2af12175badf
- Updated: 2026-10-09T07:45:04Z

## Investigation State
- **Explored paths**:
  - `05_Production_Pipeline/production_orchestrator.py` (`concat_scene_shots`, `master_scene_audio`)
  - `05_Production_Pipeline/audio_continuity_engine.py` (Mode A vs Mode B, 2-pass linear loudnorm, 4-stem mixing, dynamic ducking)
  - `05_Production_Pipeline/assemble_ep01_feature.py`, `assemble_ep04_feature.py`, `assemble_ep06_feature.py`
  - `04_Assets/audio/`, `04_Assets/audio_sfx/`, `04_Assets/archive/ep01_legacy_v1/`, `06_Exports/`
  - `tests/test_adversarial_m3_audio_engine.py` (all 6 empirical tests pass)
  - `tests/test_production_pipeline_m3.py` (all 16 tests pass)
- **Key findings**:
  1. `concat_scene_shots` uses `AudioContinuityEngine.stitch_with_audio_crossfade` as primary engine with fallback to FFmpeg filter_complex.
  2. Identified crucial audio duration sync caveat: Mode B (`acrossfade`) shrinks audio duration by `(N-1)*crossfade_dur` (e.g. 26s for Scene 05's 27 shots), whereas Mode A (`boundary_smoothing`, 30ms micro-fade qsin) preserves exact 10s shot durations with zero sync drift.
  3. Two-pass linear loudnorm (`linear=true`, I=-14 LUFS, TP=-1.0 dBTP, LRA=9-11 LU) is fully implemented and passes all adversarial stress tests including -inf silence guard.
  4. 4-Stem architecture incorporates 800Hz-3500Hz notch filter (`equalizer=f=2150:width_type=h:width=2700:g=-3.5`) and dynamic sidechain ducking (-14dB, attack=50ms, release=300ms).
  5. Audio assets: `scene01_bgm.m4a` exists at `04_Assets/audio/scene01_bgm.m4a` (178.88s, 48kHz stereo), and `ep01_scene04_festival_crowd_ambience_120s.wav` exists at `04_Assets/audio_sfx/`. Need an intelligent audio asset resolver.
  6. Ep01 scope is 10 scenes (140 shots = 23m20s). Designed `assemble_episode_master("ep01")` stitching all 10 scene masters into `06_Exports/ep01_full_feature_master_v1.mp4`.
- **Unexplored areas**: None, all objectives thoroughly investigated and validated.

## Key Decisions Made
- Formulate blueprint specifying Mode A (`boundary_smoothing`) as default for `concat_scene_shots`.
- Design `assemble_episode_master` with candidate priority resolution, `--check`, `--dry-run`, and final EBU R128 normalization.
- Author comprehensive M4 test suite `tests/test_m4_concat_audio_mastering.py`.

## Artifact Index
- `DISPATCH.md` — records dispatch instructions and requirements
- `BRIEFING.md` — working memory and identity tracking
- `progress.md` — liveness heartbeat and workflow log
- `m4_concat_audio_blueprint.md` — complete technical specification and code proposals for Worker M4
- `handoff.md` — 5-component handoff report for parent orchestrator