av-club/sidecar/ffmpeg/vocabulary.ts

/**
 * The ffmpeg surface av-club exposes, as data — the same shape as the sharp vocabulary.
 *
 * Options are spelled the way ffmpeg spells them (`c:v`, `crf`, `pix_fmt`), so ffmpeg's own
 * documentation is the reference. What is NOT here is anything that names a file: no `-i`, no output
 * path, no protocol. See docs/SECURITY.md — that single restriction is what makes the rest of this
 * safe to open up.
 */

export type FfmpegParam =
  | { kind: "int"; min: number; max: number; note?: string }
  | { kind: "number"; min: number; max: number; note?: string }
  | { kind: "enum"; values: readonly string[]; note?: string }
  | { kind: "bitrate"; note?: string };

/** Options that go BEFORE `-i`: seeking and trimming, which are far cheaper applied to the input. */
export const INPUT_OPTIONS: Record<string, FfmpegParam> = {
  ss: { kind: "number", min: 0, max: 86_400, note: "Start at this many seconds." },
  t: { kind: "number", min: 0.001, max: 86_400, note: "Take this many seconds." },
  to: { kind: "number", min: 0, max: 86_400, note: "Stop at this timestamp." },
};

/**
 * Output options.
 *
 * The encoder list is short on purpose: these are the codecs a browser plays. An encoder ffmpeg
 * happens to have compiled in is not automatically something worth publishing.
 */
export const OUTPUT_OPTIONS: Record<string, FfmpegParam> = {
  "c:v": { kind: "enum", values: ["libx264", "libvpx-vp9", "libaom-av1", "copy"], note: "Video encoder. libx264 is the one every browser plays." },
  "c:a": { kind: "enum", values: ["aac", "libopus", "copy"], note: "Audio encoder." },
  crf: { kind: "int", min: 0, max: 63, note: "Quality. Lower is better and bigger; 23 is a sane default for x264." },
  preset: { kind: "enum", values: ["ultrafast", "superfast", "veryfast", "faster", "fast", "medium", "slow", "slower", "veryslow"], note: "Encoder effort. Slower is smaller at the same quality." },
  tune: { kind: "enum", values: ["film", "animation", "grain", "stillimage", "fastdecode", "zerolatency"] },
  "profile:v": { kind: "enum", values: ["baseline", "main", "high"], note: "`high` is fine everywhere current." },
  level: { kind: "enum", values: ["3.0", "3.1", "4.0", "4.1", "4.2", "5.0", "5.1"] },
  pix_fmt: { kind: "enum", values: ["yuv420p", "yuv422p", "yuv444p"], note: "yuv420p, or Safari and QuickTime will not play it." },
  "b:v": { kind: "bitrate", note: "Target video bitrate, e.g. 2M." },
  "b:a": { kind: "bitrate", note: "Target audio bitrate, e.g. 128k." },
  maxrate: { kind: "bitrate" },
  bufsize: { kind: "bitrate" },
  r: { kind: "number", min: 1, max: 120, note: "Output frame rate." },
  g: { kind: "int", min: 1, max: 600, note: "Keyframe interval." },
  ar: { kind: "enum", values: ["22050", "44100", "48000"], note: "Audio sample rate." },
  ac: { kind: "int", min: 1, max: 2 },
  "frames:v": { kind: "int", min: 1, max: 10_000, note: "Stop after this many frames — 1 gives a poster." },
  movflags: { kind: "enum", values: ["+faststart"], note: "Moves the index to the front so playback can start before the file has arrived. Always want this for web." },
  an: { kind: "enum", values: ["1"], note: "Drop audio entirely." },
};

/** Output containers. `image2` is how a single frame comes out as a still. */
export const FORMATS: Record<string, { extension: string; describe: string }> = {
  mp4: { extension: "mp4", describe: "H.264/AAC in MP4 — plays everywhere." },
  webm: { extension: "webm", describe: "VP9/Opus. Smaller, but not on older Safari." },
  mp3: { extension: "mp3", describe: "Audio only." },
  image2: { extension: "jpg", describe: "A single frame, for poster images." },
};

/**
 * Filters, default-deny.
 *
 * ffmpeg's filter graph is a language, and most of it is arithmetic on pixels. A small, specific part
 * of it reads files or loads native code — `movie`, `subtitles`, `frei0r`, `ladspa` and relatives —
 * and those are not in this list, so they are refused. A filter nobody has classified is refused too:
 * a blocklist would silently admit whatever the next ffmpeg release adds.
 */
export const VIDEO_FILTERS: Record<string, Record<string, FfmpegParam>> = {
  scale: {
    w: { kind: "int", min: -2, max: 8192, note: "-2 keeps the aspect ratio and an even number of pixels, which h264 requires." },
    h: { kind: "int", min: -2, max: 8192 },
  },
  crop: {
    w: { kind: "int", min: 1, max: 8192 },
    h: { kind: "int", min: 1, max: 8192 },
    x: { kind: "int", min: 0, max: 8192 },
    y: { kind: "int", min: 0, max: 8192 },
  },
  fps: { fps: { kind: "number", min: 1, max: 120 } },
  format: { pix_fmts: { kind: "enum", values: ["yuv420p", "yuv422p", "yuv444p", "rgb24"] } },
  transpose: { dir: { kind: "enum", values: ["0", "1", "2", "3"] } },
  hflip: {},
  vflip: {},
  eq: {
    brightness: { kind: "number", min: -1, max: 1 },
    contrast: { kind: "number", min: -1000, max: 1000 },
    saturation: { kind: "number", min: 0, max: 3 },
    gamma: { kind: "number", min: 0.1, max: 10 },
  },
  unsharp: {
    luma_msize_x: { kind: "int", min: 3, max: 23 },
    luma_msize_y: { kind: "int", min: 3, max: 23 },
    luma_amount: { kind: "number", min: -2, max: 5 },
  },
};

export const AUDIO_FILTERS: Record<string, Record<string, FfmpegParam>> = {
  volume: { volume: { kind: "number", min: 0, max: 10 } },
  aresample: { osr: { kind: "enum", values: ["22050", "44100", "48000"] } },
  loudnorm: {
    I: { kind: "number", min: -70, max: -5, note: "Target loudness in LUFS. -16 suits the web." },
    TP: { kind: "number", min: -9, max: 0 },
  },
};

/**
 * Named presets, so a caller does not have to know encoder settings to get a web-playable file.
 *
 * This is where the media knowledge lives — the whole reason av-club is a separate repo. A consumer
 * says what the media is FOR; what that means in flags is decided here and can be revised in one
 * place for every site that uses it.
 */
export const PRESETS: Record<string, { describe: string; format: string; options: Record<string, string | number>; filters?: { v?: { name: string; args: Record<string, number | string> }[] } }> = {
  "web-1080": {
    describe: "H.264 up to 1080p. The safe default — plays in every browser.",
    format: "mp4",
    options: { "c:v": "libx264", crf: 23, preset: "medium", "profile:v": "high", pix_fmt: "yuv420p", "c:a": "aac", "b:a": "128k", movflags: "+faststart" },
    filters: { v: [{ name: "scale", args: { w: -2, h: 1080 } }] },
  },
  "web-720": {
    describe: "H.264 up to 720p.",
    format: "mp4",
    options: { "c:v": "libx264", crf: 23, preset: "medium", "profile:v": "high", pix_fmt: "yuv420p", "c:a": "aac", "b:a": "128k", movflags: "+faststart" },
    filters: { v: [{ name: "scale", args: { w: -2, h: 720 } }] },
  },
  "web-480": {
    describe: "H.264 up to 480p, for slow connections.",
    format: "mp4",
    options: { "c:v": "libx264", crf: 26, preset: "medium", "profile:v": "main", pix_fmt: "yuv420p", "c:a": "aac", "b:a": "96k", movflags: "+faststart" },
    filters: { v: [{ name: "scale", args: { w: -2, h: 480 } }] },
  },
  poster: {
    describe: "One frame as a JPEG, for a video's poster image.",
    format: "image2",
    options: { "frames:v": 1 },
  },
};