How Does SMIL Support Multi-Window Layouts?
The Synchronized Multimedia Integration Language (SMIL) enables multi-window layouts across multiple physical displays primarily through its modular layout architecture, most notably the MultiWindowLayout and HierarchicalLayout modules. By separating media synchronization from visual geometry, SMIL allows authors to declare multiple independent top-level presentation surfaces (top-level windows) or map a single extended virtual canvas across multiple physical screens.
The SMIL Layout Architecture
In standard SMIL configurations, layout definitions reside in the
document <head> within the
<layout> element. While early specifications relied
exclusively on a single <root-layout> container
representing a single screen or application window, the SMIL
specification expanded to support complex multi-surface and
multi-display setups.
Within this structure, two primary techniques manage multi-window output across physical hardware:
- **Top-Level Window Partitioning via
MultiWindowLayout** - Virtual Canvas Spanning Across Display Matrices
MultiWindowLayout
and the <topLayout> Element
The MultiWindowLayout module replaces or augments the
traditional <root-layout> element by introducing
<topLayout>.
- Independent Rendering Windows: Authors can declare
multiple
<topLayout>elements inside a single<layout>container. Each<topLayout>instance functions as an autonomous, top-level window. - Physical Screen Targeting: In operating systems or
dedicated media players configured for extended desktops, each
<topLayout>can be assigned specific screen coordinates (left,top,width,height) or designated display targets, effectively placing different windows on different physical monitors. - Nested Sub-Regions: Within each
<topLayout>, standard<region>tags define zones for video, text tickers, or images. Media elements in the<body>map directly to these regions using theregionattribute, completely independent of the playback schedule.
<smil xmlns="http://www.w3.org/ns/SMIL">
<head>
<layout>
<!-- Display 1: Primary Screen -->
<topLayout id="screen1" title="Main Display" left="0" top="0" width="1920" height="1080">
<region id="main_video" left="0" top="0" width="1920" height="1080" />
</topLayout>
<!-- Display 2: Secondary Screen -->
<topLayout id="screen2" title="Side Display" left="1920" top="0" width="1920" height="1080">
<region id="ticker" left="0" top="0" width="1920" height="200" />
<region id="side_ad" left="0" top="200" width="1920" height="880" />
</topLayout>
</layout>
</head>
<body>
<par>
<video src="hero.mp4" region="main_video" />
<text src="news.txt" region="ticker" />
<img src="promo.jpg" region="side_ad" />
</par>
</body>
</smil>Virtual Canvas Mapping (Digital Signage Configurations)
In digital signage and video wall environments, SMIL players often leverage a unified virtual desktop configuration.
- Unified Root Canvas: The author defines a single
large
<root-layout>encompassing the combined resolution of all connected monitors (e.g., 3840×1080 for two side-by-side Full HD screens). - Coordinate-Based Display Assignment: Individual
<region>elements are placed at coordinates that match the physical boundaries of each display. - Hardware Slicing: The host graphics card or digital signage media player splits the unified desktop output across the respective video output ports (such as HDMI or DisplayPort).
Synchronization Across Multiple Surfaces
A key strength of SMIL in multi-window environments is its native
timing and synchronization engine. Because all regions and windows
reside within a single SMIL document, media across different displays
can be orchestrated with millisecond accuracy using
<par> (parallel), <seq>
(sequential), and syncMaster attributes, ensuring seamless
transitions across multi-screen installations.