The SourceBuffers

Overview

The core/source-buffer directory contains the part of the code directly related to the insertion and removal of media segments.

This is done through SourceBuffers, which are JavaScript objects.

Some SourceBuffers are directly defined by the browser like the audio and video ones. Others, like for subtitles for example, are defined by the RxPlayer. Those custom SourceBuffers definitions are written in the src/custom_source_buffers directory.

SourceBuffersStore

The SourceBuffersStore is the main export from there. It facilitates the creation and destruction of SourceBuffers. More specifically, it keeps track of every SourceBuffer created for a given content.

As a rule, only ONE SourceBuffer is allowed by type of buffer (e.g. audio, video, text (subtitles), images (thumbnails)).

QueuedSourceBuffer

A QueuedSourceBuffer is a wrapper on top of a SourceBuffer (a native one or a custom RxPlayer implementation) that allows to push and remove segments sequentially. Basically, it waits for the previous action to be finished before going on the next step.

It also keeps an inventory of all segments currently contained in it, with the help of a SegmentInventory (see corresponding chapter).

It is the main interface the rest of the RxPlayer code has with SourceBuffers.

BufferGarbageCollector

The BufferGarbageCollector is a function used by the RxPlayer to periodically perform “garbage collection” manually on a given QueuedSourceBuffer.

It is based on the following building bricks:

• A clock, which is an observable emitting the current time (in seconds) when the garbage collection task should be performed

• The QueuedSourceBuffer on which the garbage collection task should run

• The maximum time margin authorized for the buffer behind the current position

• The maximum time margin authorized for the buffer ahead of the current position

Basically, each times the given clock ticks, the BufferGarbageCollector will ensure that the volume of data before and ahead of the current position does not grow into a larger value than what is configured.

The SegmentInventory

The SegmentInventory keeps track of which segments are currently bufferized to avoid unnecessary re-downloads.

You can have more information on it in the SegmentInventory documentation.