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web/libav: preallocate memory for output when remuxing

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dumbmoron 2024-08-12 18:06:59 +00:00
parent 2198a696ce
commit 940826697c
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1 changed files with 12 additions and 2 deletions
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14
web/src/lib/libav.ts
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@ -57,12 +57,16 @@ export default class LibAVWrapper {
// https://github.com/Yahweasel/libav.js/blob/7d359f69/docs/IO.md#block-writer-devices
await this.libav.mkwriterdev(outputName);
let writtenData = new Uint8Array(0);
// since we expect the output file to be roughly the same size
// as the original, preallocate its size for the output
let writtenData = new Uint8Array(blob.size), actualSize = 0;
this.libav.onwrite = (name, pos, data) => {
if (name !== outputName) return;
const newLen = Math.max(writtenData.length, pos + data.length);
actualSize = Math.max(pos + data.length, actualSize);
const newLen = Math.max(pos + data.length, writtenData.length);
if (newLen > writtenData.length) {
const newData = new Uint8Array(newLen);
newData.set(writtenData);
@ -71,6 +75,12 @@ export default class LibAVWrapper {
writtenData.set(data, pos);
};
// if we didn't need as much space as we allocated for some reason,
// shrink the buffer so that we don't inflate the file with zeros
if (writtenData.length > actualSize) {
writtenData = writtenData.slice(0, actualSize);
}
await this.libav.ffmpeg([
'-nostdin', '-y',
'-threads', this.concurrency.toString(),