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DASH: Remove "native" JS parser
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From the v4.1.0, we had 3 MPD parsers:

  - The "native" one, relying on the web's DOMParser API.

    This is historically the first one we used and still the one we rely
    by default on main thread.

  - The "WebAssembly" one, added in 2021.

    This one was initially written when we had to manage multi-megabytes
    MPD. Those took forever to parse on low-end devices but worse even
    on a PC, parsing it often (e.g. for a live content) could lead to a
    crash after several hours due to GC pressure.

    The idea was to parse the MPD in another thread (the initial
    MULTI_THREAD attempts date back from here :p) and to rely on
    WebAssembly to better control memory usage and performance (also the
    "native" one wasn't usable anyway on a WebWorker due to browser
    limitations).

    It turned out that the WebAssembly version was so light (note: we
    also rely on XML StAX parsing instead of DOM parsing which may have
    helped for that part) and fast that we didn't yet need the
    complexity of bringing another thread here.

  - The "fast js" one, added at the last `v4.1.0` release.

    This one follows attempts to make the `MULTI_THREAD` feature usable
    on non-WebAssembly devices. We noticed that other developers had
    recently made attempts for fast JS parsing without even needing the
    use of the DOMParser. They reported even faster performance due to
    much fewer XML integrity checks (which is OK for us, as MPD parsing
    performance is one of the most important aspect for us).

This commit proposes that we remove the "native" one to just replace it
by the "fast js" one.

The "fast js" one has already been used in production for more than 6
months without issue, is equal-to-faster than the native one and it
would lead to much less code.
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@peaBerberian
peaBerberian committed Sep 4, 2024
1 parent 683b02e commit 44c2921
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Showing 66 changed files with 92 additions and 4,108 deletions.
4 changes: 2 additions & 2 deletions src/core/main/worker/worker_main.ts
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Expand Up @@ -10,7 +10,7 @@ import type {
IReferenceUpdateMessage,
} from "../../../multithread_types";
import { MainThreadMessageType, WorkerMessageType } from "../../../multithread_types";
import DashFastJsParser from "../../../parsers/manifest/dash/fast-js-parser";
import DashJsParser from "../../../parsers/manifest/dash/js-parser";
import DashWasmParser from "../../../parsers/manifest/dash/wasm-parser";
import { ObservationPosition } from "../../../playback_observer";
import type { IWorkerPlaybackObservation } from "../../../playback_observer/worker_playback_observer";
Expand Down Expand Up @@ -72,7 +72,7 @@ export default function initializeWorkerMain() {
// TODO allow worker-side feature-switching? Not sure how
const dashWasmParser = new DashWasmParser();
features.dashParsers.wasm = dashWasmParser;
features.dashParsers.fastJs = DashFastJsParser;
features.dashParsers.js = DashJsParser;
features.transports.dash = createDashPipelines;

/**
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2 changes: 1 addition & 1 deletion src/features/features_object.ts
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Expand Up @@ -21,7 +21,7 @@ import type { IFeaturesObject } from "./types";
* @type {Object}
*/
const features: IFeaturesObject = {
dashParsers: { wasm: null, native: null, fastJs: null },
dashParsers: { wasm: null, js: null },
createDebugElement: null,
directfile: null,
decrypt: null,
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6 changes: 3 additions & 3 deletions src/features/list/__tests__/dash.test.ts
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@@ -1,6 +1,6 @@
import { describe, it, expect } from "vitest";
import MediaSourceContentInitializer from "../../../main_thread/init/media_source_content_initializer";
import nativeDashParser from "../../../parsers/manifest/dash/native-parser";
import dashJsParser from "../../../parsers/manifest/dash/js-parser";
import DASHFeature from "../../../transports/dash";
import type { IFeaturesObject } from "../../types";
import addDASHFeature from "../dash";
Expand All @@ -9,13 +9,13 @@ describe("Features list - DASH", () => {
it("should add DASH in the current features", () => {
const featureObject = {
transports: {},
dashParsers: { fastJs: null, native: null, wasm: null },
dashParsers: { js: null, wasm: null },
mainThreadMediaSourceInit: null,
} as unknown as IFeaturesObject;
addDASHFeature(featureObject);
expect(featureObject).toEqual({
transports: { dash: DASHFeature },
dashParsers: { native: nativeDashParser, fastJs: null, wasm: null },
dashParsers: { js: dashJsParser, wasm: null },
mainThreadMediaSourceInit: MediaSourceContentInitializer,
});
expect(featureObject.transports.dash).toBe(DASHFeature);
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5 changes: 2 additions & 3 deletions src/features/list/__tests__/dash_wasm.test.ts
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Expand Up @@ -21,12 +21,11 @@ describe("Features list - DASH WASM Parser", () => {

const featureObject = {
transports: {},
dashParsers: { native: null, fastJs: null, wasm: null },
dashParsers: { js: null, wasm: null },
} as unknown as IFeaturesObject;
DASH_WASM._addFeature(featureObject);
expect(featureObject.transports).toEqual({ dash: DASHFeature });
expect(featureObject.dashParsers.native).toEqual(null);
expect(featureObject.dashParsers.fastJs).toEqual(null);
expect(featureObject.dashParsers.js).toEqual(null);
expect(featureObject.dashParsers.wasm).toBeInstanceOf(DashWasmParser);
});
});
4 changes: 2 additions & 2 deletions src/features/list/dash.ts
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Expand Up @@ -15,7 +15,7 @@
*/

import MediaSourceContentInitializer from "../../main_thread/init/media_source_content_initializer";
import dashJsParser from "../../parsers/manifest/dash/native-parser";
import dashJsParser from "../../parsers/manifest/dash/js-parser";
import dash from "../../transports/dash";
import type { IFeaturesObject } from "../types";

Expand All @@ -27,7 +27,7 @@ function addDASHFeature(features: IFeaturesObject): void {
if (features.transports.dash === undefined) {
features.transports.dash = dash;
}
features.dashParsers.native = dashJsParser;
features.dashParsers.js = dashJsParser;
features.mainThreadMediaSourceInit = MediaSourceContentInitializer;
}

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13 changes: 2 additions & 11 deletions src/features/types.ts
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Expand Up @@ -61,12 +61,7 @@ export type IHTMLTextTracksBuffer = new (
*/
export type INativeTextTracksBuffer = new (mediaElement: IMediaElement) => SegmentSink;

export type IDashNativeParser = (
dom: Document,
args: IMPDParserArguments,
) => IDashParserResponse<string>;

export type IDashFastJsParser = (
export type IDashJsParser = (
xml: string,
args: IMPDParserArguments,
) => IDashParserResponse<string>;
Expand Down Expand Up @@ -142,11 +137,7 @@ export interface IFeaturesObject {
/**
* Entirely JavaScript-based Manifest DASH parser.
*/
fastJs: IDashFastJsParser | null;
/**
* JavaScript+Browser's DOMParser-based Manifest DASH parser.
*/
native: IDashNativeParser | null;
js: IDashJsParser | null;
};
/** Implement text track rendering through `<track>` HTML elements. */
nativeTextDisplayer: typeof NativeTextDisplayer | null;
Expand Down
52 changes: 36 additions & 16 deletions src/main_thread/init/utils/__tests__/refresh_scheduled_events_list.test.ts
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Expand Up @@ -7,36 +7,57 @@ import { describe, it, expect, vi } from "vitest";
/* eslint-disable @typescript-eslint/no-explicit-any */

describe("init - refreshScheduledEventsList", () => {
it("should correclty refresh scheduled events", async () => {
function generateEventData() {
it("should correctly refresh scheduled events", async () => {
function generateInputEventData() {
return {
type: "dash-event-stream",
value: {
schemeIdUri: "toto",
timescale: 1,
element: document.createElement("div"),
xmlData: { data: "<div />", namespaces: [] },
},
};
}
function generateOutputEventData() {
const parsedDom = new DOMParser().parseFromString(
"<toremove><div /></toremove>",
"application/xml",
).documentElement;

const element =
parsedDom.children.length > 0
? parsedDom.children[0]
: (parsedDom.childNodes[0] as HTMLElement);

return {
type: "dash-event-stream",
value: {
schemeIdUri: "toto",
timescale: 1,
element,
xmlData: { data: "<div />", namespaces: [] },
},
};
}
const manifest = {
periods: [
{
start: 0,
streamEvents: [{ start: 0, end: 1, data: generateEventData(), id: "1" }],
streamEvents: [{ start: 0, end: 1, data: generateInputEventData(), id: "1" }],
},
{
start: 10,
streamEvents: [
{ start: 11, end: 20, data: generateEventData(), id: "2" },
{ start: 12, data: generateEventData(), id: "3" },
{ start: 13, end: 13.1, data: generateEventData(), id: "4" },
{ start: 11, end: 20, data: generateInputEventData(), id: "2" },
{ start: 12, data: generateInputEventData(), id: "3" },
{ start: 13, end: 13.1, data: generateInputEventData(), id: "4" },
],
},
],
};
const oldScheduledEvents = [
{ start: 1000, end: 1000000, id: "must-disapear", _isBeingPlayed: true },
{ start: 0, end: 1, data: generateEventData(), id: "1" },
{ start: 0, end: 1, data: generateOutputEventData(), id: "1" },
];
const refreshScheduledEventsList = (
(await vi.importActual(
Expand All @@ -46,27 +67,26 @@ describe("init - refreshScheduledEventsList", () => {

const scheduledEvents = refreshScheduledEventsList(oldScheduledEvents, manifest);
expect(scheduledEvents).toEqual([
{ start: 0, end: 1, id: "1", data: generateEventData() },
{ start: 0, end: 1, id: "1", data: generateOutputEventData() },
{
start: 11,
end: 20,
id: "2",
publicEvent: { start: 11, end: 20, data: generateEventData() },
data: generateEventData(),
publicEvent: { start: 11, end: 20, data: generateOutputEventData() },
data: generateOutputEventData(),
},
{
start: 12,
end: undefined,
id: "3",
publicEvent: { start: 12, data: generateEventData() },
data: generateEventData(),
publicEvent: { start: 12, data: generateOutputEventData() },
data: generateOutputEventData(),
},
{
start: 13,
end: 13.1,
id: "4",
publicEvent: { start: 13, end: 13.1, data: generateEventData() },
data: generateEventData(),
publicEvent: { start: 13, end: 13.1, data: generateOutputEventData() },
data: generateOutputEventData(),
},
]);
});
Expand Down
4 changes: 1 addition & 3 deletions src/main_thread/init/utils/stream_events_emitter/refresh_scheduled_events_list.ts
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Expand Up @@ -41,9 +41,7 @@ function refreshScheduledEventsList(
}

let element: Element;
if (data.value.element !== undefined) {
element = data.value.element;
} else if (data.value.xmlData !== undefined) {
if (data.value.xmlData !== undefined) {
// First, we will create a parent Element defining all namespaces that
// should have been encountered until know.
// This is needed because the DOMParser API might throw when
Expand Down
104 changes: 1 addition & 103 deletions src/parsers/manifest/dash/common/indexes/timeline/__tests__/parse_s_element.test.ts
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Expand Up @@ -2,64 +2,11 @@ import { describe, it, expect, vi } from "vitest";
import log from "../../../../../../../log";
import type { ITNode } from "../../../../../../../utils/xml-parser";
import { parseXml } from "../../../../../../../utils/xml-parser";
import { parseSHTMLElement, parseSElementNode } from "../parse_s_element";
import { parseSElementNode } from "../parse_s_element";

function testNumberAttribute(attributeName: string, variableName?: string): void {
const _variableName = variableName ?? attributeName;

it(`should correctly parse an HTML S element with a correct ${attributeName} attribute`, () => {
const spyLog = vi.spyOn(log, "warn").mockImplementation(vi.fn());
const element1 = new DOMParser().parseFromString(
`<S ${attributeName}="012" />`,
"text/xml",
).childNodes[0] as Element;
expect(parseSHTMLElement(element1)).toEqual({ [_variableName]: 12 });

const element2 = new DOMParser().parseFromString(
`<S ${attributeName}="0" />`,
"text/xml",
).childNodes[0] as Element;
expect(parseSHTMLElement(element2)).toEqual({ [_variableName]: 0 });

const element3 = new DOMParser().parseFromString(
`<S ${attributeName}="-50" />`,
"text/xml",
).childNodes[0] as Element;
expect(parseSHTMLElement(element3)).toEqual({ [_variableName]: -50 });

expect(spyLog).not.toHaveBeenCalled();
spyLog.mockRestore();
});

it(`should correctly parse an HTML S element with an incorrect ${attributeName} attribute`, () => {
const spyLog = vi.spyOn(log, "warn").mockImplementation(vi.fn());
const element1 = new DOMParser().parseFromString(
`<S ${attributeName}="toto" />`,
"text/xml",
).childNodes[0] as Element;
expect(parseSHTMLElement(element1)).toEqual({});
expect(spyLog).toHaveBeenCalledTimes(1);
expect(spyLog).toHaveBeenCalledWith(`DASH: invalid ${attributeName} ("toto")`);

const element2 = new DOMParser().parseFromString(
`<S ${attributeName}="PT5M" />`,
"text/xml",
).childNodes[0] as Element;
expect(parseSHTMLElement(element2)).toEqual({});
expect(spyLog).toHaveBeenCalledTimes(2);
expect(spyLog).toHaveBeenCalledWith(`DASH: invalid ${attributeName} ("PT5M")`);

const element3 = new DOMParser().parseFromString(
`<S ${attributeName}="" />`,
"text/xml",
).childNodes[0] as Element;

expect(parseSHTMLElement(element3)).toEqual({});
expect(spyLog).toHaveBeenCalledTimes(3);
expect(spyLog).toHaveBeenCalledWith(`DASH: invalid ${attributeName} ("")`);
spyLog.mockRestore();
});

it(`should correctly parse a node S element with a correct ${attributeName} attribute`, () => {
const spyLog = vi.spyOn(log, "warn").mockImplementation(vi.fn());
const element1 = parseXml(`<S ${attributeName}="012" />`)[0] as ITNode;
Expand Down Expand Up @@ -97,43 +44,10 @@ function testNumberAttribute(attributeName: string, variableName?: string): void
}

describe("DASH Node Parsers - S", () => {
it("should correctly parse an HTML S element without attributes", () => {
const element = new DOMParser().parseFromString("<S />", "text/xml")
.childNodes[0] as Element;
expect(parseSHTMLElement(element)).toEqual({});
});

it("should correctly parse a Node S element without attributes", () => {
const element = parseXml("<S />")[0] as ITNode;
expect(parseSElementNode(element)).toEqual({});
});

testNumberAttribute("t", "start");
testNumberAttribute("r", "repeatCount");
testNumberAttribute("d", "duration");

it("should correctly parse an HTML S Element with every attributes", () => {
const element1 = new DOMParser().parseFromString(
'<S t="0" d="4" r="12" />',
"text/xml",
).childNodes[0] as Element;
expect(parseSHTMLElement(element1)).toEqual({
start: 0,
repeatCount: 12,
duration: 4,
});

const element2 = new DOMParser().parseFromString(
'<S t="99" d="4" r="0" />',
"text/xml",
).childNodes[0] as Element;
expect(parseSHTMLElement(element2)).toEqual({
start: 99,
repeatCount: 0,
duration: 4,
});
});

it("should correctly parse a node S Element with every attributes", () => {
const element1 = parseXml('<S t="0" d="4" r="12" />')[0] as ITNode;
expect(parseSElementNode(element1)).toEqual({
Expand All @@ -150,22 +64,6 @@ describe("DASH Node Parsers - S", () => {
});
});

it("should correctly parse an HTML S Element with unknown attributes", () => {
const element1 = new DOMParser().parseFromString(
'<S t="0" d="4" r="12" f="9" />',
"text/xml",
).childNodes[0] as Element;
expect(parseSHTMLElement(element1)).toEqual({
start: 0,
repeatCount: 12,
duration: 4,
});

const element2 = new DOMParser().parseFromString('<S b="7000" />', "text/xml")
.childNodes[0] as Element;
expect(parseSHTMLElement(element2)).toEqual({});
});

it("should correctly parse a node S Element with unknown attributes", () => {
const element1 = parseXml('<S t="0" d="4" r="12" f="9" />')[0] as ITNode;
expect(parseSElementNode(element1)).toEqual({
Expand Down
16 changes: 5 additions & 11 deletions src/parsers/manifest/dash/common/indexes/timeline/construct_timeline_from_elements.ts
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Expand Up @@ -18,29 +18,23 @@ import type { ITNode } from "../../../../../../utils/xml-parser";
import type { IIndexSegment } from "../../../../utils/index_helpers";
import convertElementsToIndexSegment from "./convert_element_to_index_segment";
import type { IParsedS } from "./parse_s_element";
import { parseSElementNode, parseSHTMLElement } from "./parse_s_element";
import { parseSElementNode } from "./parse_s_element";

/**
* Allows to generate the "timeline" for the "Timeline" RepresentationIndex.
* Call this function when the timeline is unknown.
* This function was added to only perform that task lazily, i.e. only when
* first needed.
* @param {Array.<Object>|HTMLCollection} elements - All S nodes constituting
* @param {Array.<Object>} elements - All S nodes constituting
* the corresponding SegmentTimeline node.
* @returns {Array.<Object>}
*/
export default function constructTimelineFromElements(
elements: ITNode[] | HTMLCollection,
elements: ITNode[],
): IIndexSegment[] {
const initialTimeline: IParsedS[] = [];
if (Array.isArray(elements)) {
for (let i = 0; i < elements.length; i++) {
initialTimeline.push(parseSElementNode(elements[i]));
}
} else {
for (let i = 0; i < elements.length; i++) {
initialTimeline.push(parseSHTMLElement(elements[i]));
}
for (let i = 0; i < elements.length; i++) {
initialTimeline.push(parseSElementNode(elements[i]));
}
const timeline: IIndexSegment[] = [];
for (let i = 0; i < initialTimeline.length; i++) {
Expand Down
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