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Implement optimized fragmented MP4 demuxing

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This commit is contained in:
David Payr
2024-12-14 21:50:51 +01:00
parent 5978110de9
commit 07689fbd8d
14 changed files with 2543 additions and 163 deletions
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src/reader.ts
+25 -11
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@@ -1,8 +1,6 @@
import { assert, binarySearchLessOrEqual, removeItem } from './misc';
import { Source } from './source';
const PAGE_SIZE = 4096;
type ReadSegment = {
start: number;
end: number;
@@ -27,32 +25,29 @@ export class Reader {
constructor(public source: Source, public maxStorableBytes = Infinity) {}
async loadRange(start: number, end: number) {
// Read rounded to the nearest page
const alignedStart = Math.floor(start / PAGE_SIZE) * PAGE_SIZE;
let alignedEnd = Math.ceil(end / PAGE_SIZE) * PAGE_SIZE;
alignedEnd = Math.min(alignedEnd, await this.source._getSize());
end = Math.min(end, await this.source._getSize());
const matchingLoadingSegment = this.loadingSegments.find(x => x.start <= alignedStart && x.end >= alignedEnd);
const matchingLoadingSegment = this.loadingSegments.find(x => x.start <= start && x.end >= end);
if (matchingLoadingSegment) {
// Simply wait for the existing promise to finish to avoid loading the same range twice
await matchingLoadingSegment.promise;
return;
}
const encasingSegmentExists = this.loadedSegments.some(x => x.start <= alignedStart && x.end >= alignedEnd);
const encasingSegmentExists = this.loadedSegments.some(x => x.start <= start && x.end >= end);
if (encasingSegmentExists) {
// Nothing to load
return;
}
const bytesPromise = this.source._read(alignedStart, alignedEnd);
const loadingSegment: LoadingSegment = { start: alignedStart, end: alignedEnd, promise: bytesPromise };
const bytesPromise = this.source._read(start, end);
const loadingSegment: LoadingSegment = { start, end, promise: bytesPromise };
this.loadingSegments.push(loadingSegment);
const bytes = await bytesPromise;
removeItem(this.loadingSegments, loadingSegment);
this.insertIntoLoadedSegments(alignedStart, bytes);
this.insertIntoLoadedSegments(start, bytes);
}
private insertIntoLoadedSegments(start: number, bytes: Uint8Array) {
@@ -136,4 +131,23 @@ export class Reader {
offset: segment.bytes.byteOffset + start - segment.start,
};
}
forgetRange(start: number, end: number) {
if (end <= start) {
return;
}
const startIndex = binarySearchLessOrEqual(this.loadedSegments, start, x => x.start);
if (startIndex === -1) {
return;
}
const segment = this.loadedSegments[startIndex]!;
if (segment.start !== start || segment.end !== end) {
return;
}
this.loadedSegments.splice(startIndex, 1);
this.totalStoredBytes -= segment.bytes.byteLength;
}
}