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/**
* Adds up the chunk delays to find out how long a APNG is
* @param {data} apngFile the APNG data
*/
const calculateApngLength = (apngFile) => {
const d = new Uint8Array(apngFile);
// https://wiki.mozilla.org/APNG_Specification#.60fcTL.60:_The_Frame_Control_Chunk
let duration = 0;
for (let i = 0; i < d.length; i++) {
// Find fcTL header (66 63 54 4C)
if (
d[i] === 0x66 &&
d[i + 1] === 0x63 &&
d[i + 2] === 0x54 &&
d[i + 3] === 0x4c
) {
// numerator and denominator
const delayNum = Number(d[i + 23]);
const delayDen = Number(d[i + 25]);
let delay;
// minimum is 100ms
if (delayDen === 0) {
delay = delayNum / 100;
} else {
delay = delayNum / delayDen;
}
duration += delay;
}
}
return duration * 10;
};
export default calculateApngLength;
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