ISO IEC 14496-30-2018 amd1-2022 PDF

Full title and description

ISO/IEC 14496-30:2018/Amd 1:2022 — Information technology — Coding of audio‑visual objects — Part 30: Timed text and other visual overlays in ISO base media file format — Amendment 1: Timing improvements. This amendment revises timing and presentation rules for timed text (e.g., TTML and WebVTT) and other visual overlays carried in ISO Base Media File Format (ISOBMFF) tracks to improve synchronization, reduce artefacts at sample boundaries, and clarify processing behaviour for implementers.

Abstract

This amendment updates ISO/IEC 14496-30:2018 with targeted timing improvements for timed text and visual overlay streams in ISOBMFF containers. It clarifies that rendering is driven by presentation time (taking edit lists into account), specifies refined timing-processing rules for TTML documents with ttp:timeBase="media", defines handling for empty or redundant samples, introduces flags and behaviours to avoid flicker at sample boundaries, and formalizes WebVTT sample configuration. The changes are intended to increase interoperability across players, streaming systems and authoring tools, and to improve subtitle/overlay timing accuracy in segmented and adaptive delivery scenarios.

General information

• Status: Published
• Publication date: 21 June 2022
• Publisher: ISO / IEC (ISO/IEC JTC 1/SC 29)
• ICS / categories: 35.040.40 (Coding of audio, video, multimedia and hypermedia information)
• Edition / version: Edition 2 (Amendment 1 to ISO/IEC 14496-30:2018)
• Number of pages: 6

Scope

This amendment applies to Part 30 of the MPEG-4 suite (ISO/IEC 14496-30:2018). It modifies and clarifies how timed text and other visual overlay samples carried in ISOBMFF tracks are timed and processed by renderers. The scope includes presentation-time driven rendering, interaction with edit lists, TTML timing resolution when ttp:timeBase is 'media', treatment of redundant/empty samples, and definitions for WebVTT sample entries and related metadata. The amendment is intended for authoring, packaging and playback implementations that carry subtitle/caption and overlay content inside MP4/ISOBMFF files and segments.

Key topics and requirements

• Presentation-time driven rendering: rendering is defined to occur at presentation time (with edit lists applied) and sample durations may be trimmed by edit lists.
• TTML timing processing: specific rules for processing TTML documents carried in tracks when ttp:timeBase="media", including use of the TTML "resolve timing" procedure and mapping to intermediate synchronic documents (ISDs).
• Sample clipping and ISD clipping: ISDs produced by TTML processors are clipped to the sample's timing interval to avoid overrun and unintended display outside sample boundaries.
• Redundancy and empty-sample handling: introduction of behaviour and flags (e.g., sample_has_redundancy semantics) allowing renderers to extend prior content or skip redundant samples to reduce flicker and processing overhead.
• WebVTT sample configuration: formalizes how WebVTT data is carried in ISOBMFF samples and what configuration metadata may be included.
• Guidance for streaming and segmentation: rules help ensure smooth subtitle behaviour across segment boundaries for DASH/HLS and similar adaptive streaming systems.
• Interoperability constraints and profiles: references to hypothetical render models and profile constraints (e.g., IMSC1-style constraints) to ensure predictable rendering across platforms.

Typical use and users

Implementers of media players and decoders, streaming-platform engineers, packagers and authoring tools, subtitle and caption creation vendors, broadcasters and OTT service providers, accessibility and localization teams, and archive/ingest engineers. Typical activities include authoring timed text tracks, packaging subtitles into MP4/ISOBMFF segments, implementing TTML/WebVTT renderers, and ensuring subtitle timing interoperability in segmented streaming workflows.

Related standards

ISO/IEC 14496-12 (ISO Base Media File Format) — foundational container and edit-list semantics; ISO/IEC 14496-14 (MP4 file format) — common file usage of ISOBMFF; W3C TTML (Timed Text Markup Language) — document timing and resolve-timing rules referenced by this amendment; IMSC1 (TTML profiles for subtitles/captions) — profile constraints and hypothetical render models; W3C WebVTT — text-track format formalized for ISOBMFF samples; other parts of the MPEG-4 family that handle packaging and track semantics.

Keywords

timed text, TTML, WebVTT, subtitles, captions, ISOBMFF, ISO base media file format, MP4, timed overlays, presentation time, edit list, redundancy, IMSC1, synchronization, streaming, DASH, HLS

FAQ

Q: What is this standard?

A: This is Amendment 1 (2022) to ISO/IEC 14496-30:2018, titled "Timing improvements". It updates Part 30 of the MPEG-4 timed-text and overlay specifications to clarify and improve timing and rendering behaviour for timed text and visual overlays carried in ISO base media file format tracks.

Q: What does it cover?

A: It covers timing-related processing rules: presentation-time driven rendering (with edit-list effects), TTML timing resolution when ttp:timeBase is "media", clipping of ISDs to sample intervals, handling of redundant or empty samples, WebVTT sample configuration in ISOBMFF, and guidance to improve subtitle timing across segments and platforms.

Q: Who typically uses it?

A: Media player and decoder developers, streaming platform and packager engineers, subtitle/caption authoring and localization teams, broadcasters, OTT services, and anyone authoring or consuming timed text and overlay data in MP4/ISOBMFF files or segments.

Q: Is it current or superseded?

A: This document is an amendment published on 21 June 2022 to ISO/IEC 14496-30:2018 (Edition 2). It is a published amendment (6 pages) that modifies the 2018 edition; it does not replace the base Part 30 document but supplements and changes specific timing behaviour defined there. Implementers should apply both the base Part 30 text and this amendment together.

Q: Is it part of a series?

A: Yes. ISO/IEC 14496 is a multipart standard (the MPEG-4 family). Part 30 is one part focused on timed text and visual overlays; related parts include ISO/IEC 14496-12 (ISOBMFF), 14496-14 (MP4 file format), and other parts that define codecs, packaging and related behaviours.

Q: What are the key keywords?

A: timed text, TTML, WebVTT, subtitles, captions, ISOBMFF, edit lists, presentation time, sample duration, redundancy, IMSC1, streaming.