ISO/IEC 14496-17:2006

Overview - ISO/IEC 14496-17:2006 (Streaming text format)

ISO/IEC 14496-17:2006 defines a transport-agnostic streaming text format for timed presentation of textual data in audiovisual services. It provides a low-bitrate, byte-stream representation for subtitles, karaoke lyrics and other timed text components that can be carried as separate streams alongside audio/video. The standard specifies the concept of text streams, text access units, and a decoder configuration (TextConfig) that signals the text data format (for example, 3GPP Timed Text). It focuses on efficient carriage, timing, random access and reasonable error robustness for bandwidth-constrained networks such as mobile IP.

Key topics and technical requirements

• Text stream and access unit model: A text stream is a byte stream carrying sequential text access units; each access unit has a single timestamp that specifies when it must be presented.
• TextConfig: A configuration box that signals the textFormat (e.g., 0x01 = 3GPP Timed Text) and format-specific parameters required by the decoder.
• 3GPP text support: The standard defines how 3GPP Timed Text (per 3GPP TS 26.245) is carried - including text samples, text strings (UTF-8/UTF-16) and text modifiers, plus sample descriptions (fonts, positioning).
• Framing for transport (TTU): Introduces Timed Text Units (TTUs) - a flexible framing structure to aggregate small text access units into larger transport packets or to fragment large units across packets, improving adaptation to different transports and error resilience.
• Transport-agnostic signaling: Specifies usage within MPEG-4 (streamType 0x0D, objectTypeIndication 0x08) while allowing transport over RTP, MPEG-2 Systems, optical media or other IP/broadcast systems.
• Interleaving and in-band sample descriptions: Allows sample descriptions to be carried in-band or out-of-band; each text sample refers to one sample description index.

Applications and who uses it

• Mobile service providers and streaming platform engineers needing low-bitrate subtitles and timed text for bandwidth-limited networks.
• Broadcasters and OTT providers implementing subtitle/closed-caption carriage over RTP, MPEG-2 Systems or MP4-based workflows.
• Device manufacturers and media player developers building timed-text decoders compatible with MPEG-4 systems and 3GPP timed text.
• Content creators for Karaoke, accessibility (hard-of-hearing captions), multi-language subtitle distribution, and lightweight standalone text streaming services.

Related standards

• ISO/IEC 14496 (MPEG-4) family - particularly Part 12 (ISO base media file format) and Part 14 (MP4 file format) for storage/packaging.
• ISO/IEC 14496-18:2004 (Font compression and streaming)
• 3GPP TS 26.245 (Timed Text format) - defines the timed text sample and modifier formats referenced by this part.
• Transport systems referenced: RTP, MPEG-2 Systems (for broadcast/optical media transport)

Keywords: ISO/IEC 14496-17, streaming text format, timed text, TTU, 3GPP Timed Text, subtitles, low bitrate, TextConfig, text access unit, MPEG-4.