<Audio> at composition root resolves to duration=Infinity in ffmpeg filter graph #4

Summary

A bare <Audio src={...} /> placed at the root of a <Composition> (no endAt prop, no wrapping <Sequence>) causes the renderer to emit duration=Infinity into the ffmpeg atrim filter, which crashes the render.

Reproduction

// MyChapter.tsx
import { CanvasElement, Audio, staticFile } from '@rendiv/core';

export const CHAPTER_DURATION = 3814;

export const MyChapter = () => (
  <CanvasElement id="MyChapter">
    <Audio src={staticFile('audio/chapter.mp3')} />
    {/* ...other content sized to CHAPTER_DURATION... */}
  </CanvasElement>
);

// index.tsx
<Composition
  id=\"MyChapter\"
  component={MyChapter}
  durationInFrames={CHAPTER_DURATION}
  fps={30}
  width={1920}
  height={1080}
/>

Run:

rendiv render src/index.tsx MyChapter out/MyChapter.mp4

Actual

FFmpeg exited with code 234:
[Parsed_atrim_0 @ 0x...] Unable to parse option value \"Infinity\" as duration
Error applying option 'duration' to filter 'atrim': Invalid argument
Failed to set value '[1:a]atrim=start=0.000000:duration=Infinity,asetpts=PTS-STARTPTS[aout]'
  for option 'filter_complex': Invalid argument

Expected

The renderer should treat `` without an explicit `endAt` as bounded by the parent composition's `durationInFrames` — same behavior as Remotion.

Workaround

Explicitly pass `endAt`:
```tsx
<Audio src={staticFile('audio/chapter.mp3')} endAt={CHAPTER_DURATION} />
```

This works, but every chapter master in the project needed the same one-line fix, and the failure mode (`duration=Infinity` from ffmpeg) was very far from the cause.

Suggested fixes (any one would help; all three would be ideal)

1. Default `endAt` to composition duration. When `` has no `endAt` and no wrapping ``, treat it as `endAt = compositionDurationInFrames`.

2. Guard the filter-graph emitter. Before serializing `atrim=duration=${value}`, `assert(Number.isFinite(value))` and throw with a useful message, e.g.:

   `Audio src="..." resolved to infinite duration. Pass endAt={N} or wrap in .`

3. Mount-time lint. Walk the composition tree once and warn for any `` / `

Environment

• `@rendiv/core`: ^0.1.0
• `@rendiv/cli`: ^0.1.0
• ffmpeg: 7.0.2-static
• OS: Debian inside Docker container (headless)