46 lines
1.1 KiB
TypeScript
46 lines
1.1 KiB
TypeScript
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const MP4_BRANDS = new Set([
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"avc1",
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"dash",
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"isom",
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"M4A ",
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"M4B ",
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"M4P ",
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"M4V ",
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"mp41",
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"mp42",
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"MSNV",
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]);
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function fourCharacters(bytes: Uint8Array, offset: number) {
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return String.fromCharCode(...bytes.slice(offset, offset + 4));
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}
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function isMp4Brand(brand: string) {
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return (
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MP4_BRANDS.has(brand) ||
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/^iso[2-9]$/.test(brand) ||
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/^3g[2p]$/.test(brand.slice(0, 3))
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);
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}
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/** Rejects HTML/JSON/error payloads and non-MP4 containers before download. */
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export function hasMp4FileSignature(input: ArrayBuffer | Uint8Array) {
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const bytes = input instanceof Uint8Array ? input : new Uint8Array(input);
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if (bytes.byteLength < 12 || fourCharacters(bytes, 4) !== "ftyp") {
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return false;
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}
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const declaredSize = new DataView(
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bytes.buffer,
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bytes.byteOffset,
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bytes.byteLength,
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).getUint32(0);
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const boxEnd = Math.min(
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bytes.byteLength,
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declaredSize >= 12 ? declaredSize : bytes.byteLength,
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);
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for (let offset = 8; offset + 4 <= boxEnd; offset += 4) {
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if (isMp4Brand(fourCharacters(bytes, offset))) return true;
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}
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return false;
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}
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