port: P4 -- the intro video plays inside the boot sequence

The exporter transcodes ADV.wmv and S00A.wmv to Ogg Theora and records the exact
ffmpeg command in the manifest, per MISSION §6, so a modder who dislikes the
quality re-runs one line rather than reverse-engineering what was done.

Quality was MEASURED, not judged: SSIM against the decoded source over a 10 s
sample is 0.9863 / 0.9896 / 0.9924 at -q:v 6 / 8 / 10, and at 200 % zoom on the
reel's hardest case -- fine serif text and soft gradients over near-black, where
Theora breaks first -- q8 is indistinguishable. So MISSION §6's permitted
FFmpeg-GDExtension fallback is NOT needed and is NOT being proposed. No new
runtime dependency.

-ac 2 because the source is 6-channel WMA Pro; that downmix is a decision, so it
lives in the recorded command rather than in prose.

Encoding is cached on a .cmd sidecar holding the command and the source size --
any change to either re-encodes. export/ is still regenerated wholesale; this is
derived state validating derived state, not a hand-edit, and without it every
re-export pays ~4 minutes to produce a byte-identical file.

The player renders INTO the design SubViewport. Parenting it to the Boot node
played the movie to the window instead, and every captured frame came out black
-- which is worth more than a capture-bug note: a movie outside the 1280x720
design space is outside the coordinate system every screen is expressed in.

(A) skips a movie, because Q9 measured that (title at 57 s vs a 193 s baseline).

NOT VERIFIED, and stated as such: audible playback. This container has no audio
device and Godot falls back to the dummy driver. The Vorbis stream exists, is
2-channel and decodes; whether Godot emits it is unconfirmed.

docs/DECISIONS.md

@@ -682,3 +682,71 @@ renderer. The three known differences are unchanged: `title` 6 (paint-order tie)
   carry `rotation_deg` in a future FORMAT v3 because carrying a decoded field the
   renderer ignores beats dropping it, but it will not draw it until the
   divergence question is settled.
+
+---
+
+## P4 — the intro video, 2026-08-29
+
+### Theora at 720p is fine here, and no runtime dependency is requested
+
+MISSION §6 anticipated that Theora might be too poor at 720p and permitted the
+FFmpeg-GDExtension fallback to be **proposed**. It is not needed, and this was
+measured rather than judged by eye alone. SSIM against the decoded source over a
+10 s sample: **0.9863 at `-q:v 6`, 0.9896 at 8, 0.9924 at 10**. At 200 % zoom on
+the reel's hardest case — fine serif text and soft gradients over near-black,
+where Theora breaks first — q8 is indistinguishable from the source.
+
+`-q:v 8`, and **no GDExtension is being proposed or adopted**.
+
+`-ac 2` because the source is **6-channel** WMA Pro and Godot's Theora path is
+not a surround one. That downmix is a decision, so it lives in the recorded
+command where a modder can see and change it rather than in prose.
+
+### The exact command is in the manifest, per MISSION §6
+
+`export/manifest.json` gains a `videos` array, each entry carrying the verbatim
+`ffmpeg` line that produced it. A modder who dislikes the quality re-runs one
+line instead of reverse-engineering what was done to their video — which is the
+whole reason this project converts the disc rather than reading it at runtime.
+
+### A cache, and why that is not a hand-edit
+
+`export/` is regenerated wholesale, but re-encoding 232 s of video on every run
+costs ~4 minutes to produce a byte-identical file, and an exporter nobody re-runs
+is worse than a cache. So each movie gets a `.cmd` sidecar recording the command
+and the source size, and the encode is skipped only when both match exactly. Any
+change to either re-encodes. This is derived state validating derived state, not
+a hand-edit.
+
+### The player renders into the design viewport, not beside it
+
+First attempt parented the `VideoStreamPlayer` to the Boot node. It played, and
+every captured frame was **black**: the capture reads the SubViewport, and the
+player was rendering to the window. Worth stating as more than a capture bug —
+everything this port draws composes in the export's own 1280×720 design space,
+and a movie outside that space is outside the coordinate system every screen is
+expressed in.
+
+### Ⓐ skips, because Q9 measured it
+
+The only input the port handles so far. HANDOFF Q9: one Ⓐ press skips a movie,
+measured — the title was reached at 57 s against a 193 s baseline. Menu
+navigation is still P5.
+
+## P4 gate
+
+`godot --path port -- --boot --film=…` runs
+`publisher_logo → developer_logos → ADV.ogv → title`, unattended. The filmstrip
+shows the SQUARE ENIX ident, then the reel's live-action-styled CG, then the
+title. The movie's place in the boot is **measured, not decoded** — Q9 decodes
+`ADVERTISE_MOVIE → ADV.wmv` from the movie manifest, but *where it sits in the
+boot order* is what the RE agent watched, and `authored/flow.json` says so.
+
+### What I cannot verify from here
+
+**Audible playback.** This container has no audio device — Godot falls back to
+the dummy driver. What is verified is that the Vorbis stream exists in the
+transcode, is 2-channel, and decodes. Whether Godot emits it audibly is
+unconfirmed and is stated as unconfirmed rather than assumed from the stream's
+presence. It is a cheap check for anyone with a sound device and an impossible
+one here.