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/* eslint no-bitwise: "off" */
/**
* Adds up the frame delays to find out how long a GIF is
* I totally didn't steal this
* @param {data} gifFile the GIF data
*/
const calculateGifLength = (gifFile) => {
const d = new Uint8Array(gifFile);
// Thanks to http://justinsomnia.org/2006/10/gif-animation-duration-calculation/
// And http://www.w3.org/Graphics/GIF/spec-gif89a.txt
let duration = 0;
for (let i = 0; i < d.length; i++) {
// Find a Graphic Control Extension hex(21F904__ ____ __00)
if (d[i] === 0x21
&& d[i + 1] === 0xF9
&& d[i + 2] === 0x04
&& d[i + 7] === 0x00) {
// Swap 5th and 6th bytes to get the delay per frame
const delay = (d[i + 5] << 8) | (d[i + 4] & 0xFF);
// Should be aware browsers have a minimum frame delay
// e.g. 6ms for IE, 2ms modern browsers (50fps)
duration += delay < 2 ? 10 : delay;
}
}
return duration * 10;
};
export default calculateGifLength;
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