# gizlang:mp4

MP4 files (ISO/IEC 14496-12 and 14496-14) of a video track (H.264, HEVC or AV1) and an AAC-LC track (ISO/IEC 14496-3). A browser plays the file as it arrives: the index (moov) comes before the samples.

```gizlang
import * as Mp4 from "gizlang:mp4";
```

## Types

### `Track`

```gizlang
type Track = { codec: string; width: i64; height: i64; fps: i64; headers: Vec<bytes>; frames: Vec<bytes>; keys: Vec<bool>; }
```

A video track: its codec ("h264", "hevc" or "av1"), size, frames a second, parameter sets, and frames with their key
flags.

- `codec`: `string`
- `width`: `i64`
- `height`: `i64`
- `fps`: `i64`
- `headers`: `Vec<bytes>`
- `frames`: `Vec<bytes>`
- `keys`: `Vec<bool>`

### `Aac`

```gizlang
type Aac = { rate: i64; channels: i64; config: bytes; frames: Vec<bytes>; delay: i64; samples: i64; }
```

An AAC-LC track: its rate, channels, AudioSpecificConfig, and raw frames of 1024 samples a channel. The first
`delay` samples it decodes to are the encoder's priming, before the audio; `samples` is the audio's length.

- `rate`: `i64`
- `channels`: `i64`
- `config`: `bytes`
- `frames`: `Vec<bytes>`
- `delay`: `i64`
- `samples`: `i64`

## Functions

### `mp4`

```gizlang
function mp4(video: Track, audio: Option<Aac>): bytes
```

The MP4 file of `video` and, when given, `audio`. The samples of each track are one chunk, the video's first.

Effects: fail.