The Stream

Overview

Even if the API is the front-facing block of code in the Rx-player, the Stream is the part of the code actually starting the logic behind playing a content.

Its code is written in the src/core/stream directory. More specifically, all code needed in the rest of the code should be exported by its “index file” src/core/stream/index.ts.

Every time you’re calling the API to load a new video, the Stream function is called by it with a handful of arguments.

The Stream does then the major part of the job and communicate back its progress to the API through events.

                 +-----------+
 1. LOAD VIDEO   |           |      2. CALLS
---------------> |    API    | -------------------+
                 |           |                    |
                 +-----------+                    |
                       ^                          v
                       |                    +--------------+
                       |   3. EMIT EVENTS   |              |
                       +------------------- |    STREAM    |
                                            |              |
                                            +--------------+

Basically, the job of the Stream is to:

• initialize the content (creating the MediaSource, downloading the manifest)

• Connect most core parts of the player together, such as adaptive streaming management, segment pipelines, DRMs, speed management…

• Call with the right argument the PeriodBufferManager, which will download and push segment to be decoded by the browser.

As such, during the various events happening on content playback, the Stream will create / destroy / update various player blocks. Such example of blocks are:

• Adaptive streaming management

• DRM management

• Manifest loading, parsing and refreshing

• Buffer management

• …

Usage

Concretely, the Stream is a function which returns an Observable. This Observable:

• will automatically load the described content on subscription

• will automatically stop and clean-up infos related to the content on unsubscription

• communicate on various streaming events through emitted notifications

• throw in the case of a fatal error (i.e. an error interrupting playback)

Communication between the API and the Stream

Objects emitted by the Observable is the only way the Stream should be able to communicate with the API.

The API is then able to communicate back to the Stream, either:

• by Observable provided by the API as arguments when the Stream function was called

• by emitting through Subject provided by the Stream, as a payload of one of its event

Thus, there is three ways the API and Stream can communicate:

• API -> Stream: When the Stream function is called (so a single time)

• Stream -> API: Through events emitted by the returned Observable

• API -> Stream: Through Observables/Subjects the Stream is in possession of.

Emitted Events

Events allows the Stream to reports milestones of the content playback, such as when the content is ready to play.

It’s also a way for the Stream to communicate informations about the content and give some controls to the user.

For example, as available audio languages are only known after the manifest has been downloaded and parsed, and as it is most of all a user preference, the Stream can emit to the API RxJS Subjects allowing the API to “choose” at any time the wanted language.

The SpeedManager

The SpeedManager is the part of the Stream updating the playback speed of the content.

Playback speed can be updated on two occasions:

• the API set a new Speed (speed$ Observable).

• the content needs to build its buffer.

  In which case, the playback speed will be set to 0 (paused) even if the API set another speed. The regular speed will be set when enough buffer is available.

The StallingManager

The StallingManager listens to various browser events and properties to detect when the player is “stalled” (i.e. stuck on the current position).

It then try to adopt a strategy to easily get out of this situation if it can.