ISO/IEC 14496-18:2004
Information technology — Coding of audio-visual objects — Part 18: Font compression and streaming
Information technology — Coding of audio-visual objects — Part 18: Font compression and streaming
- Статус документа:
- Действующий
- Формат:
- Электронный (PDF)
- Количество страниц:
- 18
- Дата публикации:
- 30 июня 2004 г.
- Издание:
- ISO/IEC IS 14496 edition 1 version 1
- ICS:
- 35.040
ISO/IEC 14496-18:2004 is part of the MPEG-4 suite of International Standards. It specifies font data representation, compression and streaming, providing an efficient mechanism to embed font data in MPEG-4 encoded presentations. It also defines MPEG-4 Text profiles and levels. The ISO/IEC 14496 (MPEG-4) series has been developed by MPEG (Motion Picture Experts Group) and defines the set of technologies for compression, encoding and delivery of complex audio-visual scenes composed of different media objects: video objects (natural or synthetic video); audio objects; still images; text and vector graphics; computer-animated images. MPEG-4 provides a standardized way to: represent the content of audio-visual objects; describe the composition of these objects in compound media scenes; encode, multiplex and synchronize the data associated with the media objects; transport the media presentation over different channels; interact with the audio-visual scene at the receiver's end. An essential part of almost any media presentation involves text objects that are created using specific or custom fonts. Font selection determines the appearance of text in multimedia content and also plays a critical role in the overall scene composition, since the metric properties of a font are used for textual parts of multimedia content layout. Many thousands of fonts are available today for use in content creation. In order to assure the readability and legibility of text as well as the correct appearance and layout of content, the font data must be included (embedded) with the text objects as part of the multimedia presentation.
Abstract
Overview
ISO/IEC 14496-18:2004 - part of the MPEG‑4 family - specifies font compression and streaming for embedding and delivering font data in MPEG‑4 audio‑visual presentations. The standard adopts OpenType (version 1.4) as the font data format (fonts must include a Unicode ‘cmap’), defines a lossless compression mechanism for TrueType / OpenType with TrueType outlines, and describes the coded font data stream and MPEG‑4 Text profiles and levels used to render text reliably across platforms and constrained devices.
Key topics and requirements
- Font data format
- Uses OpenType as the canonical file format for transmitted fonts.
- Requires a Unicode character map (‘cmap’) to ensure correct character mapping.
- Compression technology
- Specifies a lossless compression scheme (MicroType® Express 2.0 is adopted in the standard) optimized for TrueType outlines.
- Compression targets font tables (especially the ‘glyf’ glyph table) using table‑aware methods to reduce size while preserving typographic features.
- Supports mixed compressed/uncompressed tables and random access to compressed data so a font rasterizer can render glyphs without decompressing the whole font.
- Compressed font layout
- Maintains the SFNT/OpenType table directory structure; introduces an ‘act3’ table to map original tables to compressed/uncompressed blocks (including TTC support).
- Font data stream
- Defines structure of font streams, access units, time base, and font decoder configuration for streaming delivery and synchronization with other media.
- Text profiles and levels
- Specifies MPEG‑4 Text profiles such as Simple Text, Advanced Simple Text and Main Text, with levels that constrain capabilities for interoperability.
Applications and who uses it
- Multimedia and streaming platform vendors embedding custom fonts in video, interactive content and captions.
- Browser, player and font rasterizer implementers ensuring correct appearance and layout in MPEG‑4 scenes.
- Mobile and embedded device manufacturers optimizing memory/ROM/RAM usage for on‑device text rendering.
- Content creators and streaming services requiring reliable font embedding and multilingual support in bandwidth‑limited delivery.
Related standards
- ISO/IEC 14496‑1 (Systems) - synchronization and container model
- ISO/IEC 14496‑11 (Scene description and application engine)
- ISO/IEC 14496‑17 (Streaming text format)
- OpenType font file specification (normative reference for table formats)
Keywords: ISO/IEC 14496-18:2004, MPEG‑4, font compression and streaming, OpenType, TrueType, MicroType Express, font embedding, font streaming, font data stream, ACT3, glyf, text profiles.
Технические детали
- Технический комитет
- ISO/IEC JTC 1/SC 29 - Coding of audio, picture, multimedia and hypermedia information
- SKU
- ISO/IEC 14496-18:2004
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