32 lines
1000 B
TypeScript
32 lines
1000 B
TypeScript
/**
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* @returns duration in ms
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*/
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export default function getGifDuration(image: HTMLImageElement) {
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const src = image.src;
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return fetch(src)
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.then(response => response.arrayBuffer())
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.then(arrayBuffer => {
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const d = new Uint8Array(arrayBuffer);
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// Thanks to http://justinsomnia.org/2006/10/gif-animation-duration-calculation/
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// And http://www.w3.org/Graphics/GIF/spec-gif89a.txt
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let duration = 0;
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for(let i = 0, length = d.length; i < length; ++i) {
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// Find a Graphic Control Extension hex(21F904__ ____ __00)
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if(d[i] == 0x21
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&& d[i + 1] == 0xF9
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&& d[i + 2] == 0x04
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&& d[i + 7] == 0x00) {
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// Swap 5th and 6th bytes to get the delay per frame
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const delay = (d[i + 5] << 8) | (d[i + 4] & 0xFF);
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// Should be aware browsers have a minimum frame delay
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// e.g. 6ms for IE, 2ms modern browsers (50fps)
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duration += delay < 2 ? 10 : delay;
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}
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}
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return duration / 1000;
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});
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}
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