JavaScript API available in GPAC. More...

Collaboration diagram for JavaScript APIs:

Modules
	JS Core API for libgpac
	JavaScript API for libgpac core tools.

	JS Filter API
	JavaScript API for filters.

	XMLHttpRequest API
	XMLHttpRequest API.

	EVG JS API
	Embedded Vector Graphics JavaScript API.

	Compositor API
	GPAC Compositor and Scene API.

	Storage API
	Storage API.

	WebGL API
	WebGL API.

	JS FilterSession API
	JavaScript API for FilterSession.

	JS DASH Adaptation API
	JavaScript API for DASH client adaptation algorithm.

	JS HTTP output API
	JavaScript API for httpout filter.

Detailed Description

Parts of the GPAC code can be modified at run-time using JavaScript. This part of the documentation describes the various APIs used in GPAC.

For SVG and DOM scenegraph API, see https://www.w3.org/TR/SVGTiny12/svgudom.html.

For BIFS and VRML scenegraph, see https://www.web3d.org/documents/specifications/14772/V2.0/part1/javascript.html

SVG and BIFS APIs are automatically loaded when loading an SVG or BIFS scene with script nodes. They cannot be loaded in another way.

The JSFilter API is loaded through a dedicated filter, see gpac -h jsf.

All other APIs shall be loaded by the parent script (scene or JSFilter) as ECMAScript modules using the import directive.

GPAC uses the amazing QuickJS engine for JavaScript support: https://bellard.org/quickjs/quickjs.html. Although not JIT-enabled, it is small, fast and cross-platform which ensures the same behaviour on all devices.

The module loader is the same as the QuickJS libc module loader (https://bellard.org/quickjs/quickjs.html#Modules), except that it checks for .so, .dll or .dylib extensions for C modules.

This means that JS C modules as defined in QuickJS could also be used (https://bellard.org/quickjs/quickjs.html#C-Modules)

Warning: support for C modules is still not fully tested

There is currently no support for non-local modules (http, https ...).

The default GPAC compilation includes the following modules from QuickJS:

'std': documentation https://bellard.org/quickjs/quickjs.html#std-module
'os': documentation https://bellard.org/quickjs/quickjs.html#os-module (see below)

GPAC constants used in the API (error code, property types, specific flags for functions) are exported:

using the same name as native code, e.g. GF_STATS_LOCAL, GF_FILTER_SAP_1, etc...
in the global object of the javascript context

Unless indicated otherwise, all errors are handled through exceptions. An exception object contains a code (integer) attribute and optionally a message (string) attribute.

Types and interfaces are described using WebIDL, see https://heycam.github.io/webidl/, with some slight modifications.

Warning: These IDL files are only intended to document the APIs, and are likely useless for other purposes.

Notes on QuickJS 'os' module support:

Workers are supported on OSX, Windows, iOS and Linux; final dereference of the worker object will end the worker thread.
On Windows, the exec function retuns an array rather than an int when run in asynchronous mode. The waitpid function will return an array where the first item is this pid object when the process is over, to keep the same behavious as under non Windows systems.
On Windows, the exec function ignores uid, gid and user-specified stdin/stderr/stdout.