# gizai:video/decode

any audio or video file decoded with ffmpeg.

```gizlang
import * as Decode from "gizai:video/decode";
```

## Functions

### `ffmpegOut`

```gizlang
function ffmpegOut(sys: System, ffmpeg: string, args: Vec<string>, input: bytes = b""): bytes throws string
```

What the program `ffmpeg` (its name on PATH, or a path) writes to its standard output when it runs with `args`, its
standard input `input`; its error output when it fails.

Effects: fail, read, write, io.

### `ffprobe`

```gizlang
function ffprobe(ffmpeg: string): string
```

The ffprobe beside the program `ffmpeg`: in its folder, else on PATH.

Effects: fail.

### `audio`

```gizlang
function audio(sys: System, ffmpeg: string, path: string, most: f64 = 0.0, rate: i64 = 0, channels: i64 = 0, bits: i64 = 32): Wave throws string
```

The samples of the audio in the file `path` (any audio or video file ffmpeg reads: MP3, AAC, M4A, FLAC, Ogg, MP4,
WebM, ...) through the program `ffmpeg`: at most `most` seconds (when above 0), so a long file stays small;
resampled by ffmpeg to `rate` and mixed to `channels` (0: the file's own); as `bits`-bit samples (32: floats; 16:
PCM, as a reference decoder that reads 16-bit WAV gets them).

Effects: fail, read, write, io.

### `mono`

```gizlang
function mono(wave: Wave, rate: i64): Vec<f32>
```

The mean of the channels of `wave`, at `rate` (resampled as torchaudio does): a speech model's mono input.

Effects: fail.

### `probe`

```gizlang
function probe(sys: System, ffmpeg: string, path: string): Result<Vec<i64>, string>
```

The width, height, (whole) frame rate and frames (by its duration; 0: not known) of the first video stream of the
file `path`, by ffprobe next to `ffmpeg`.

Effects: fail, read, write, io.

### `frameIndices`

```gizlang
function frameIndices(rate: i64, target: i64, count: i64): Vec<i64>
```

The source frames that WanGP picks for `count` frames at `target` fps from a video of `rate` fps (its
_resample_frame_indices from frame 0, which H3 and Qwen's video readers share).

Effects: fail.

### `frames`

```gizlang
function frames(sys: System, ffmpeg: string, path: string, wanted: Vec<i64>, width: i64, height: i64, mask: bool): Result<Vec<bytes>, string>
```

The frames `wanted` (ascending indices, as frameIndices gives them) of the video `path`, as `width` x `height` RGB
bytes each (a mask: one byte each, 1 where the gray is over 127.5), resized by Lanczos as WanGP's
preprocess_video_with_mask does; those past its end are left out.

Effects: fail, read, write, io.

### `filtered`

```gizlang
function filtered(sys: System, ffmpeg: string, path: string, n: i64, filter: string, format: string, size: i64): Vec<bytes> throws string
```

At most the first `n` frames of the video `path` through ffmpeg's `filter`, as `format` (rgb24, gray) frames of
`size` bytes.

Effects: fail, read, write, io.