# Rendering and checking

> How to render stills, transparent frames and videos, set quality and bitrate, and check an export against the floor before anyone sees it.

raea renders the same tree the viewer gets, so a still from it is the truth about layout: fonts, footage, 3D and text
overflow only show up in pixels. `raea check` then measures what a still can't, such as a word clipped for three
frames, a stretch of black or a voice buried under music. This page covers both.

## Stills

Render the frames you want to look at as PNGs:

```sh
raea render piece.tsx --at 15,63,144,270 -o stills/      # four frames, as stills/frame-00000.png and on
raea render piece.tsx --frame 120 -o frame-120.png       # one frame, to one file
raea render piece.tsx --alpha -o frames/                 # every frame as a transparent PNG, for another editor
```

Pick the moments that matter, look at all of them at once, fix everything they show, and look again. A contact sheet
of a finished video shows the whole piece in one image:

```sh
raea media sheet piece.mp4 -o sheet.png
```

## Video

```sh
raea render piece.tsx -o piece.mp4
raea render piece.tsx --composition wide -o wide.mp4   # one of several compositions in the file
```

An MP4 from raea is H.264 in yuv420p. On a Mac it is encoded with VideoToolbox (H.264 High, AAC audio); on Linux and
Windows with openh264 (H.264 Constrained Baseline, Opus audio).

The output's folder must exist: `-o out/piece.mp4` needs `out/` already there.

## Quality and bitrate

By default the bitrate follows the size and frame rate: about 20 Mbit/s at 1080p30 and 80 at 4K30.

| Flag | Use it for |
|---|---|
| `--quality draft` | Fast previews |
| `--quality high` | Most deliveries |
| `--quality master` | Final exports of motion graphics and type: keeps thin type and hard edges clean |
| `--quality 0.85` | A constant quality from 0 to 1, if the presets don't fit |
| `--kbps 12000` | A fixed bitrate |
| `--10bit` | 10-bit output |

`--quality` asks for constant quality: each frame gets the bits it needs, so a flat motion graphic stays small and a
busy one stays clean.

Blotchy dark areas come from the encoder, not the composition. Export dark material as PNG frames and encode them
with more bits for the darks:

```sh
RAEA_READBACK=rgba raea render piece.tsx -o frames/
```

## A share copy

A raea MP4 is standard but large. For a copy any player and any upload takes, re-encode it with ffmpeg:

```sh
ffmpeg -i film.mp4 -c:v libx264 -preset slow -crf 23 -maxrate 2600k -bufsize 5200k -pix_fmt yuv420p -c:a aac -b:a 128k -movflags +faststart film-share.mp4
```

## The quick check

```sh
raea check piece.tsx --quick
```

The quick check renders three stills of a composition and measures its text: clipped, cramped, inside the safe areas
and large enough to read. It takes about a second. Run it after every save. Add `--platform tiktok` (or `reels`,
`shorts`) to check against that platform's buttons and captions.

## The full check

Render with a manifest, then check the export:

```sh
raea render piece.tsx -o piece.mp4 --manifest render.json
raea check piece.mp4 --manifest render.json --words words.json --platform tiktok -o check.json
```

The manifest records where every element was on every frame, so the check can say which element a problem belongs
to. The full check measures:

- clipped text, text under the platform's buttons, and text over a face
- captions on screen too briefly to read, and caption contrast against the pixels behind them
- frozen stretches and flashing past the safe limit
- cues that miss the word they were tied to (with `--words`)
- loudness, sound that stops dead, and sound that fights the voice
- blotching in dark areas

Each finding is ranked P0 (broken) to P3 (polish) and comes with its fix. The command exits 1 while any P0 or P1
stands, so a script or an agent can stop on it. `-o check.json` writes the findings for a later review.

An exception in the composition fails the render itself and names the line: a value that turned into NaN, keyframes
out of order, a phrase `word()` can't find, or a missing prop.

## Loudness

When the composition has a `<Mix>`, the export comes out at -14 LUFS integrated (within 1) with true peak at or below
-1 dBTP, which is what the major platforms play back at.

## Mistakes to avoid

- Judging layout from the code. Text overflow and contrast against footage only show in pixels.
- Checking frame 0 only. Most problems are at cues and joins.
- Calling it done without listening. The voice must stay clear over the music, and every sound should land.
- Rendering a new version over the old one. Render `piece-v2.mp4` beside `piece.mp4`.