@sub37/captions-renderer

This is the main element that handles captions rendering and allows styiling them with custom CSS properties (described below). All the areas in which subtitles get rendered are considered as regions to achieve a uniformed behavior.

Importing

The minimum requirement to make @sub37/captions-renderer usable is to import it as a side-effect. Importing it like this, will make captions-renderer to be registered onto window's custom elements registry.

import "@sub37/captions-renderer`;

It also exposes some properties that might require you to import them as classicly. For example:

import type { OrchestratorSettings } from "@sub37/captions-renderer";
import { CSSVAR_TEXT_COLOR, ... } from "@sub37/captions-renderer";

Rendering behaviors

Captions are known to have three types of behaviors when they get rendered. This is regardless of using @sub27/captions-renderer.

• Pop-on
• Roll-up
• Paint-on

Each of these is supported by captions-renderer, but it is not the only responsible for them to happen. Continue reading to understand how they can be obtained.

Pop-on

Pop-on mode is the most classic rendering mode: captions gets rendered and remain visible for the track's pre-established amount of time. Then they get removed to leave place to other cues.

This behavior is automatically supported by captions-renderer.

Roll-up

Roll-up mode was popular in old television subtitles and it is deployed today in captions like Youtube's. It consists into painting the whole line and, once the available space ends, push the whole line up to leave space to another line. Once the available region space is reached (tipically 2 or 3 lines), older lines gets hidden.

Cues following roll-up, could be splitted into different regions that proceed distinctly. This might be useful to represent some dialogs.

captions-renderer supports this behavior by default. Cues are splitted by words to allow it to determine how many lines should be occupied by each cue.

Paint-on

Paint-on is one of the most interesting rendering mode, as it goes hand in hand with the previous two modes, especially roll-up. It consists into rendering each word with a different time from the previous or the next one.

This might be useful to obtain a speaker-like effect.

captions-renderer supports this by default, but to achieve the timing, tracks, adapters implementation and subtitle format must support this.

For example, WebVTT standard supports timestamps, which allow words to be splitted inside the tracks. Then, @sub37/webvtt-adapter supports parsing and normalization of these timestamps.

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Properties

Some properties are available to customize the rendering experience. These properties should be considered as defaults replacements, but might be ignored if provided tracks have such properties.

These properties can be set like follows:

const renderer = document.getElementsByTagName("captions-renderer")[0];

renderer.setRegionProperties({ ... });

These properties are described into an exposed typescript interface:

import type { OrchestratorSettings } from "@sub37/captions-renderer";

Supported Properties

Property name	Default	Description
lines	2	The maximum amount of lines that should be rendered by this element before hiding the previous lines. Is overridden by tracks' regions lines property.
shiftDownFirstLine	false	Allows obtaining a Youtube-like effect, where the first line is shifted down if no other lines are available to be showed.

Custom CSS variables

import { CSSVAR_TEXT_COLOR, ... } from "@sub37/captions-renderer";

CSS Variable Name	Javascript Constant Name	Default	Description
--sub37-text-color	CSSVAR_TEXT_COLOR	#FFF	Allows changing the color of text. This text overrides the color harcoded into provided tracks
--sub37-text-bg-color	CSSVAR_TEXT_BG_COLOR	rgba(0,0,0,0.7)	This is the background color. Set to transparent to remove it.
--sub37-region-bg-color	CSSVAR_REGION_BG_COLOR	rgba(0,0,0,0.4)	This is the background color of the regions. Set to transparent to remove it.
--sub37-bottom-spacing	CSSVAR_BOTTOM_SPACING	0px	This is the amount of space that regions should leave from bottom. This might be useful to make the regions move, for example, to show controls.
--sub37-bottom-transition	CSSVAR_BOTTOM_TRANSITION	0s linear	This is the transition proprieties that can be applied to regions when --sub37-bottom-spacing gets changed. Make it smoooooth, baby!

Testing

This package uses the sub37 sample page (packages/sample/pages/sub37-example) to run the tests. Playwright automatically navigates starts the server and navigates there.

Assuming that dependencies have been already installed, to run tests, run the following command:

$ npm test