Running in MultiThreading mode

Overview

The RxPlayer can rely on a WebWorker to run its main logic, effectively running in a separate thread from your application.

Here is some high level schema of how the RxPlayer roughly works without and with a WebWorker:

Running the RxPlayer without a WebWorker (the default):

+-------------------------------------------------------------------------------+
| Main thread (also running the UI)                                             |
|                                                                               |
| +------------------+     +----------------------+    +----------------------+ |
| | Your Application | --> |  RxPlayer Main [1]   | -> |   RxPlayer Core [2]  | |
| +------------------+     +----------------------+    +----------------------+ |
+-------------------------------------------------------------------------------+

Running with a WebWorker:

+----------------------------------------------------+
| Main thread (also running the UI)                  |
|                                                    |
| +------------------+      +----------------------+ |
| | Your Application | ---> |  RxPlayer Main [1]   | |
| +------------------+      +----------------------+ |
+--------------------------------------|-------------+
                                       | (messages)
+--------------------------------------|-------------+
| WebWorker                            V             |
|                           +----------------------+ |
|                           |  RxPlayer Core [2]   | |
|                           +----------------------+ |
+----------------------------------------------------+


[1] RxPlayer Main: Exposes an API to your application, performs some high-level
media monitoring, handles content decryption, displays text tracks and interacts
with web API that are only usable in the main thread.

[2] RxPlayer Core: Loads and parses the Manifest as well as media segments that
will be be played. Also monitors what's being played and will be played to
ensure a smooth playback.

This can be interesting for performance reasons, especially if you encounter one of the following situations:

  • Your application run on devices on which you can encounter performance issues. Here loading contents in a multithread mode might bring a better experience, such as a more responsive application and less rebuffering.

    We also noticed on various smart TV devices targeted by Canal+ noticeably far fewer unexpected media quality drops (and consequently, a much more stable video quality). This is because most of those drops were linked to heavy processing performed by the full application, which has an effect on the RxPlayer’s adaptive and networking logic.

    When running in “multithread” mode, performance issues coming from the application will influence much less negatively the RxPlayer code (and vice-versa), as its main logic will run in a separate thread.

  • Your application is very dynamic and you cannot afford to have a big media buffer (for example because you play live contents, because you’re playing very high quality content on a device with limited memory or both).

    Here the issue is that lengthy computations started by your application may prevent temporarily the RxPlayer from loading new media data. If the media buffer is small to begin with, we may be left with playback being frozen if the end of the buffer is reached before the RxPlayer had time to load new media data.

    When running in “multithreading” mode, loading segments (and in browsers supporting the feature, even buffering segments) is perfomed concurrently to any computation linked to your user interface, ensuring that this important buffering operation can run without being blocked.

If you do not encounter those situations, the advantages of “multithread” mode may be less evident. In any case, you may want to test that mode to see if it is improving your application.

About it being an “experimental” feature

This “multithread” mode is added as an “experimental” feature.

Like all other experimental features, it is considered stable enough to run in production. What we mean by “experimental” in the RxPlayer API is just that we may change its API at any RxPlayer version without impacting the RxPlayer’s major version due to semantic versionning principles.

For example, a new minor RxPlayer version could bring with it a complete API change regarding the corresponding MULTI_THREAD feature. Still, potential changes would be fully documented on that release’s release note and changelog file.

The choice of labeling this feature as experimental has been made so we can have more freedom if we find ways to provide sensible improvements to its API in the future.

Quick start

You can just test this feature quickly by running the following code:

// Import the RxPlayer (here the minimal version, but it also works with the
// default import)
import RxPlayer from "rx-player/minimal";

// Import the MULTI_THREAD experimental feature
import { MULTI_THREAD } from "rx-player/experimental/features";

// To simplify this example, we'll directly import "embedded" versions of the
// supplementary code used by the `MULTI_THREAD` feature.
// We could also load them on demand through URLs
import {
    EMBEDDED_WORKER,    // Code which will run in the "Worker"
    EMBEDDED_DASH_WASM, // To be able to play DASH contents
} from "rx-player/experimental/features/embeds";

// Add the MULTI_THREAD feature, like any other feature
RxPlayer.addFeatures([MULTI_THREAD]);

// Instantiate your player as usual
const player = new RxPlayer(/* your usual options */);

// After instantiation, you can at any time "attach" a WebWorker so any
// following `loadVideo` call can rely on it when possible.
player.attachWorker({
    workerUrl: EMBEDDED_WORKER,
    dashWasmUrl: EMBEDDED_DASH_WASM,
});

// Any further call to `loadVideo` may rely on WebWorker if possible (see
// limitations below)
player.loadVideo({
    /* ... */
});

// As a long as a content is loaded (or even loading or reloading), you can know
// if we rely on a WebWorker to play it by calling:
const currentModeInfo = player.getCurrentModeInformation();
if (currentModeInfo === null) {
    console.info("No content loaded."); // Note that this may also happen when an
                                        // error prevented the content from loading.
} else if (currentModeInfo.useWorker) {
    console.info("We're running the RxPlayer's main logic in a WebWorker!");
} else {
    console.info("We're running completely in main thread.");
}

Limitations

Note that the "multithread" mode will only run on a loadVideo call if all the following conditions are respected:

  • Your supported platforms both are compatible to the WebWorker browser feature (the great majority are) and WebAssembly (very old platforms might not).

  • You’ve added the MULTI_THREAD feature to the RxPlayer class (as shown in examples) before that loadVideo call.

  • You’ve called the attachWorker RxPlayer method (as shown in examples) before the loadVideo call on that same RxPlayer instance.

  • You’re playing a DASH content (through the "dash" transport option of the loadVideo call).

  • You’re not using any of those unsupported loadVideo options:

    • manifestLoader

    • segmentLoader

  • If using the representationFilter loadVideo option is defined, it is under a string form (see corresponding documentation page.

  • You did not force the "main" mode through the mode loadVideo option.

If any of those conditions may not be respected by your application, you might also want to be able to rely on the usual “main” mode (which runs everything on main thread).

Thankfully, this is very easy to do:

  • If you rely on the minimal build of the RxPlayer, ensure you’ve added the feature for the wanted streaming protocol(s).

    For example to both be able to play DASH contents on the main thread and through a WebWorker, you may do:

    import RxPlayer from "rx-player/minimal";
import { MULTI_THREAD } from "rx-player/experimental/features";
import { DASH } from "rx-player/features";

RxPlayer.addFeatures([
    // Allow DASH playback on the main thread
    DASH,

    // Allow DASH playback in "multithread" mode
    MULTI_THREAD,
]);

// ...

  • If you rely on the default RxPlayer build, you’ve nothing special to do, the DASH and SMOOTH features being already imported by default.

Also note that the addFeatures call and the attachWorker call may be performed in any order and at any point in time, even after some contents have already been loaded. This can for example allow dynamic importing of the MULTI_THREAD feature after some contents have already been played on the main thread.

How to rely on “multithread” mode

Step 1: Obtaining the Worker file and the WebAssembly file

The RxPlayer will need to be able to obtain two files to be able to run in multithread mode:

  • worker.js: The “worker” file, which will run in a WebWorker concurrently to your application.

  • mpd-parser.wasm: The DASH WebAssembly parser, today the only supported transport’s parser in a “multithread” scenario (Microsoft Smooth streaming, local contents and Metaplaylist are not yet supported).

You can find them at any of the following places:

  • The easiest way is to just import in your application the “embedded” versions of each of them, exported through the "rx-player/experimental/features/embeds" path:

    import {
  EMBEDDED_WORKER, // "embedded" version of the `worker.js` file
  EMBEDDED_DASH_WASM, // "embedded" version of the `mpd-parser.wasm` file
} from "rx-player/experimental/features/embeds";

    This allows to bypass the need to store and serve separately those two files. Note however that including those “embeds” in your application may sensibly increase its size.

    If you would prefer more control and a smaller bundle size, you may instead consider the other following ways to load those as separate files. This will lead to smaller file sizes and they will only be loaded on demand, but at a maintenance cost: you’ll have to store and serve those files yourself as well as not forget to update them each time you update the RxPlayer.

  • With every release note published on GitHub (you should only use the files linked to the RxPlayer’s version you’re using), as worker.js and mpd-parser.wasm respectively.

  • They are also available as respectively as dist/worker.js and dist/mpd-parser.wasm from the root directory of the project published on npm. As such, they might already be found in your project’s directory, for example in the node_modules directory (most probably in node_modules/rx-player/dist/ depending on your project).

Once you’ve retrieved those files and unless you relied on the embedded versions, you will need to store them and give its URL to the RxPlayer so it will be able to load them (embedded versions may be used directly instead, like an URL, in the attachWorker method shown below).

Step 2: importing the MULTI_THREAD feature and adding it

The MULTI_THREAD feature, then needs to be imported through the rx-player/experimental/features path and added to the RxPlayer’s class (and not an instance, addFeatures being a static method), like any other feature:

// Import the RxPlayer
// (here through the "minimal" build, though it doesn't change for other builds)
import RxPlayer from "rx-player/minimal";
import { MULTI_THREAD } from "rx-player/experimental/features";

RxPlayer.addFeatures([MULTI_THREAD]);

The point of this step is to provide to the RxPlayer the logic to “link” to a WebWorker. It is a form of dependency injection. That code is not present by default in RxPlayer builds to reduce bundle size when that feature isn’t needed.

Step 3: Attaching a WebWorker to your RxPlayer instance

After instantiating an RxPlayer, you can link it to its own WebWorker by calling the attachWorker method on this instance and by providing both the worker.js and mpd-parser.wasm files by providing their URL (obtained in step 1) - or the embedded version - to it:

const player = new RxPlayer({ /* ... */ });
player.attachWorker({
    workerUrl: URL_TO_WORKER_FILE,
    dashWasmUrl: URL_TO_DASH_WASM_FILE,
});

Step 4: Load a content

That should be all!

Now all contents that are compatible with the “multithread” mode should rely on the WebWorker. You can look at the limitations listed on this page to know what are the exact conditions and how you can still rely on the regular “main” mode for other contents.

You can know at any time whether a loaded content is relying on a WebWorker (“multithread” mode) or not (“main” mode), by calling the getCurrentModeInformation method:

const currentModeInfo = player.getCurrentModeInformation();
if (currentModeInfo === null) {
    console.info("No content loaded."); // Note that this may also happen when an
    // error prevented the content from loading.
} else if (currentModeInfo.useWorker) {
    console.info("We're running the RxPlayer's main logic in a WebWorker!");
} else {
    console.info("We're running completely in main thread.");
}

Running in MultiThreading mode

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