A Playback object is a queue of Playback Frame objects and a collection of Playback Stream objects.

Methods

playback.queueFrame(frame)

Adds the frame object to the playback queue.

Returns the new value for playback.availableMemory.

playback.openStream(stream)

Attaches the stream object to this playback. There must not already be an attached stream with the same .name property as this one.

All playback objects start with a 'playback' stream already open. The stream object in that case is the same as the playback object.

playback.closeStream(identifier)

Close the playback stream with the given identifier. The stream must currently exist, or an error is thrown.

Closing the 'playback' stream terminates the entire playback, clears the queue and prevents further frames from being added to the queue.

Properties

playback.name

Always 'playback'. This is the stream name of the playback object.

playback.width, playback.height

It's possible to have multiple video streams of different sizes, and at different positions. The total dimensions of the video space, if known. Individual video streams do not need to cover the entire video space.

These values will be Infinity if they are unknown.

playback.backgroundColor

A CSS color-value string for the background of the video space. By default, it is transparent.

playback.allocatedMemory

A number representing the maximum amount of memory we plan to be using at any one point in time (not in total) for this playback, in bytes.

By default this value is equivalent to screen.width * screen.height * 4 * 2, which is enough memory to store two copies of the user's entire screen as RGBA pixel data. (This is a completely arbitrary default, a rough guess at what is reasonable, and very much open to re-evaluation.)

playback.usedMemory

The sum of the .usedMemory values of each frame currently in the queue

Another way of looking at it is when a frame is added to the queue, its .usedMemory value is added to this value, and when it is taken off the queue its .usedMemory value is subtracted again.

playback.availableMemory

The same as (playback.allocatedMemory - playback.usedMemory).

It might be negative, these values are more of an experimental guideline than something to be strictly enforced.

Frames

Frame Properties

frame.delay

Time, in milliseconds, that should have elapsed since the previous frame in this stream.

frame.forStream

Identifier string for the stream that this frame is meant to be a part of.

frame.usedMemory

For a frame that represents pixel data or audio sample data, this should be the approximate size in bytes of the raw data involved. Non-data frames can have 0 for this value.

Frame Methods

frame.enter(playback, stream)

Method called to tell the frame that it is time for it to "go".

Streams

Most of the properties and methods depend on the kind of stream:

• Video Streams
• Audio Streams

Stream Properties

stream.name

Identifier string for the stream. It needs to be unique, but only in the context of this playback, not globally.

Video Streams

Video Stream Properties

video.width, video.height

Pixel dimensions of the video buffer.

video.top, video.left

Pixel offset from the top-left corner of the playback video space.

Usually there will be one video stream with the same .width and .height as the playback video space, and zero for .top and .left

video.zOrder

Usually, multiple overlapping video streams are overlaid in the order they were added, with the most recently-added one on top. Setting this property allows a later-added video stream to appear underneath an earlier-added one.

video.isOpaque

true if the video is guaranteed to have no transparent or semi-transparent pixels, false if not.

Audio Streams

Audio Stream Properties

audio.forChannel

Should be 'left', 'right' or 'mono'.