Fix captions template background; document browser flag after test render

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019yhnsd9RDz7jDSUUX7oEcH

.claude/skills/remotion-video/SKILL.md

@@ -76,6 +76,8 @@ export const Hello = ({ title }: { title: string }) => {
 - Rendering needs Chromium and ffmpeg (Remotion installs/handles these); first render can be slow.
 
 ## Common problems
+- **Can't download the browser (no internet / locked-down machine)**: point Remotion at an installed Chromium:
+  `npx remotion render <Id> out/video.mp4 --browser-executable=/path/to/chromium --chrome-mode=chrome-for-testing`
 - **Blank/white frames**: an asset path is wrong; use `staticFile()`.
 - **Flicker**: an image or font not loaded; use `<Img>` and `@remotion/google-fonts`.
 - **Slow render**: lower resolution/fps while testing, or use `--concurrency`.

.claude/skills/remotion-video/templates/captions.md

@@ -8,7 +8,7 @@ import { AbsoluteFill, useCurrentFrame, useVideoConfig } from "remotion";
 
 type Word = { text: string; start: number; end: number }; // seconds
 
-export const Captions = ({ words }: { words: Word[] }) => {
+export const Captions = ({ words, background = "#111" }: { words: Word[]; background?: string }) => {
   const frame = useCurrentFrame();
   const { fps } = useVideoConfig();
   const t = frame / fps;
@@ -19,7 +19,7 @@ export const Captions = ({ words }: { words: Word[] }) => {
   const visible = words.slice(Math.floor(i / 5) * 5, Math.floor(i / 5) * 5 + 5);
 
   return (
-    <AbsoluteFill style={{ justifyContent: "flex-end", alignItems: "center", paddingBottom: 200 }}>
+    <AbsoluteFill style={{ backgroundColor: background, justifyContent: "flex-end", alignItems: "center", paddingBottom: 200 }}>
       <div style={{ fontSize: 72, fontWeight: 800, color: "white", textShadow: "0 4px 12px black", textAlign: "center", maxWidth: "80%" }}>
         {visible.map((w, k) => (
           <span key={k} style={{ color: t >= w.start && t < w.end ? "#ffd400" : "white", marginRight: 16 }}>
@@ -34,4 +34,5 @@ export const Captions = ({ words }: { words: Word[] }) => {
 
 Tips
 - Get word times from a transcription tool (e.g. `@remotion/captions` or Whisper) and save them as JSON in `public/`.
-- Layer it over the video: `<AbsoluteFill><OffthreadVideo src={staticFile("clip.mp4")} /><Captions words={words} /></AbsoluteFill>`.
+- `background` is the backdrop when there is no video. Pass `"transparent"` when layering over a video.
+- Layer it over the video: `<AbsoluteFill><OffthreadVideo src={staticFile("clip.mp4")} /><Captions words={words} background="transparent" /></AbsoluteFill>`.