hvml

HVML Parser for Node.js

HVML (Hypervideo Markup Language) is a video metadata vocabulary. It covers three main classes of metadata:

• Technical details, like the available resolutions or codecs of a media file;
• Artistic details, like who appears in a given movie or what awards it has won; and
• Interactive UI instructions for compatible video players such as RedBlue.

HVML is designed to be human-friendly enough to write by hand in most cases. This library is not required in order to use it; it just provides an imperative API for working with it programmatically.

Installation

yarn add hvml

or

npm install hvml

Example Usage

const { HVML, Video } = require( 'hvml' );

const hvml = new HVML( './hvml.xml' );
hvml.ready.then( () => {
  // Instance methods available now
  console.log( hvml.toJson() );
} );

const video = new Video( {
  "type": ["personal", "documentary"],
  "lang": "en-US",
  "id": "welcome-to-my-channel",
} );
video.setTitle( 'Welcome to My Channel!' );
video.setTitle( 'チャンネルへようこそ！', 'ja' );
// The Video types `personal` and `documentary` combine
// to create an implicit "vlog episode" semantic.
console.log( video.isVlogEpisode() ); // true

API

HVML

A Class representing the hvml root element.

Constructor: new HVML(path, [config])

• path: HVML file to be read.
• config: (optional) Configuration object with keys:
  • schemaPath Path to validation schema. Defaults to rng/hvml.rng (relative to node_modules/hvml/).
  • schemaType: Type of validation schema, rng for RELAX NG or xsd for XML Schema Definition. Currently only rng is supported. Defaults to rng.
  • encoding: readFile character encoding. Defaults to utf8.

Returns Object, an instance of HVML.

Instance Properties

.ready

Promise that resolves when your HVML file and the internal schema used for validation are both successfully read from the file system.

The Promise itself returns a libxmljs object representing the XML tree of the file. This object is also accessible as the instance property .xml, so you don’t need to capture it on your first then().

.xml

Object representing the XML tree of your HVML file, as returned from libxmljs.

This is mostly just used internally but it’s provided as a convenience for custom operations.

.hvmlPath

String. The HVML file path specified in the constructor.

Instance Methods

.toJson()

Transforms the current HVML tree to its JSON representation (i.e. an object literal).

Returns Object.

.validate([xmllintPath])

Validates the HVML file against an internal RELAX NG schema.

• xmllintPath: Path where Node can find xmllint¹. Defaults to xmllint (which assumes it is somewhere in your system’s $PATH, such as /usr/bin/).

Returns a Promise that

• Resolves to true on validation success; or
• Rejects with an object on validation error, for example:

  {
    "message": "./bad.hvml:3: element ovml: Relax-NG validity error : Expecting element hvml, got ovml",
    "error": "Expecting element hvml, got ovml",
    "file": "./bad.hvml",
    "line": "3",
    "type": "validity",
    "expecting": "hvml",
    "got": "ovml"
  }

¹ xmllint is a command-line tool written in C which performs XML validation according to schema rules. Due to the added complexity of porting this utility to JavaScript, .validate() currently requires the xmllint binary to be installed on your system and available to Node. It comes bundled with libxml2, which you may already have if you work with XML a lot.

If you don’t have libxml2 installed, you must download it and compile the source code using the following steps:

cd libxml2/
./autogen.sh
configure
make
make install

We realize this is a pain but we’d rather ship the feature than be blocked by a lack of C/C++ experience. Pull requests welcome!

Video

A Class representing a video element.

Constructor: new Video([config])

• config: (optional) Configuration object with keys:
  • type: Space-separated string or array containing valid video types (narrative, documentary, ad, personal, historical).
  • lang: A BCP 47 language/region tag, e.g. en or en-US.
  • id: An XML/HTML-style unique ID for querying.

Returns Object, an instance of Video.

Example

const { Video } = require( 'hvml' );
const video = new Video( {
  "type": ["personal", "documentary"],
  "lang": "en-US",
  "id": "welcome-to-my-channel",
} );

Static Methods

isValidType(type)

Checks if the given video type is allowed in HVML.

• type: String of individual type to check.

Returns Boolean.

Example

const { Video } = require( 'hvml' );
console.log( Video.isValidType( 'narrative' ) ); // true
console.log( Video.isValidType( 'big-chungus' ) ); // false

Instance Methods

hasType(type)

Checks if a Video object has a given type set.

Returns Boolean.

Example

const { Video } = require( 'hvml' );
const video = new Video( {
  "type": ["personal", "documentary"],
  "lang": "en-US",
  "id": "welcome-to-my-channel",
} );
console.log( Video.hasType( 'documentary' ) ); // true
console.log( Video.hasType( 'ad' ) ); // false

isVlogEpisode()

Convenience method. Checks if a Video object contains the special type combination personal + documentary.

Returns Boolean.

Example

const { Video } = require( 'hvml' );
const video = new Video( {
  "type": ["personal", "documentary"],
  "lang": "en-US",
  "id": "welcome-to-my-channel",
} );
console.log( video.isVlogEpisode() ); // true

isArchived()

Convenience method. Checks if a Video object contains the special type combination personal + historical.

Returns Boolean.

Example

const { Video } = require( 'hvml' );
const video = new Video( {
  "type": ["personal", "historical"],
  "lang": "en-US",
  "id": "welcome-to-my-channel",
} );
console.log( video.isArchived() ); // true