苹果QuickTime文件格式规范详解

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"快速时间文件格式规范" 快速时间文件格式（QuickTime File Format）是由苹果公司开发的一种多媒体容器格式，用于存储音频、视频和其他相关数据。该格式被广泛应用于苹果的操作系统，如Mac OS X和iOS，以及一些跨平台的应用程序。QuickTime文件格式规范详细描述了如何组织和编码这些多媒体数据，以便于存储、播放和编辑。规范内容包括以下几个关键方面： 1. 文件结构：QuickTime文件基于ISO基础媒体文件格式，采用Box结构，每个Box包含特定的信息，如文件头、时间轴、媒体数据等。Box可以嵌套，使得文件结构灵活且可扩展。 2. 时间轴（Track）：QuickTime文件中的每个音视频流都被称为一个“轨道”。每个轨道包含一系列的样本，每个样本代表一段时间内的媒体数据。时间轴还包含了关于轨道的元数据，如类型、时间戳、持续时间和同步信息。 3. 数据编码：QuickTime支持多种编解码器，如H.264视频编码和AAC音频编码。文件中可以包含编解码器的元数据，帮助播放器识别并正确解码数据。 4. 音频和视频处理：QuickTime文件格式支持各种音频和视频特性，如交错视频、多通道音频、变帧率视频等。它还提供了对回放速度控制、音视频同步和时间码的支持。 5. 导出和导入：QuickTime格式允许应用程序导出或导入媒体数据，这使得与其他格式之间的转换变得可能。例如，可以将QuickTime电影转换为其他常见的视频格式，如MP4或MOV。 6. 扩展性：QuickTime格式通过扩展Box类型来适应新的功能和技术。这种灵活性使得QuickTime能够适应未来可能出现的新编码标准和技术发展。 7. 兼容性和版权保护：虽然QuickTime最初是为苹果产品设计的，但它也支持在非苹果设备上播放。此外，文件中可以包含版权信息和数字权限管理（DRM）机制，以保护内容不被非法复制和分发。 8. 应用开发：QuickTime文件格式规范为开发者提供详细的指南，帮助他们创建能够读取、写入和操作QuickTime文件的应用程序。这包括对API的使用说明，以及如何处理错误和异常的建议。总结来说，QuickTime文件格式规范是一份详尽的技术文档，它定义了如何构建和解析QuickTime文件，以实现高效的多媒体数据存储和处理。对于开发多媒体应用或需要与QuickTime格式交互的程序员而言，这份规范是不可或缺的参考材料。

QuickTime files are described in general, rather than how they are supported on a specific computing platform

or in a specific programming language. As a result, the file format information is presented in a tabular

manner, rather than in coded data structures. Similarly, field names are presented in English rather than as

programming language tags. Furthermore, to the extent possible, data types are described generically. For

example, this book uses “32-bit signed integer” rather than “long” to define a 32-bit integer value.

QuickTime files are used to store QuickTime movies, as well as other data. If you are writing an application

that parses QuickTime files, you should recognize that there may be non-movie data in the files.

Licensing Information

The QuickTime File Format Specification is provided for informational purposes. Apple may have patents,

patent applications, trademarks, copyrights, or other intellectual property rights covering subject matter in

this document. The furnishing of this document does not give you a license to any patents, trademarks,

copyrights, or other intellectual property.

Important: For more information about licensing the QuickTime File Format, contact: Apple, Inc., Software

Licensing Department, 12545 Riata Vista Circle, MS 198 3-SWL, Austin, TX 78727. Email Address:

sw.license@apple.com

Special Fonts

All code listings, reserved words, and the names of actual data structures, constants, fields, parameters, and

routines are shown code voice.

Words that appear in boldface are key terms or concepts and are defined in the glossary.

Updates to This Specification

For updates or changes to this specification, go to the QuickTime documentation site at

QuickTime Reference Library

and click the File Format Specification link.

For More Information

For information about membership in Apple’s developer program and developer technical support, you

should go to this URL:

Apple Developer

For information on registering signatures, file types, and other technical information, contact

Licensing Information

INTRODUCTION

Introduction to QuickTime File Format Specification

QuickTime movies are stored on disk, using two basic structures for storing information: atoms (also known

as simple atoms or classic atoms), and QT atoms. To understand how QuickTime movies are stored, you need

to understand the basic atom structures described in this chapter. Most atoms you encounter in the QuickTime

File Format are simple or classic atoms. Both simple atoms and QT atoms, however, allow you to construct

arbitrarily complex hierarchical data structures. Both also allow your application to ignore data they don’t

understand.

Media Description

A QuickTime file stores the description of its media separately from the media data. The description is called

the movie resource, movie atom, or simply the movie, and contains information such as the number of tracks,

the video compression format, and timing information. The movie resource also contains an index describing

where all the media data is stored.

The media data is the actual sample data, such as video frames and audio samples, used in the movie. The

media data may be stored in the same file as the QuickTime movie, in a separate file, in multiple files, in

alternate sources such as databases or real-time streams, or in some combination of these.

Atoms

The basic data unit in a QuickTime file is the atom. Each atom contains size and type fields that precede any

other data. The size field indicates the total number of bytes in the atom, including the size and type fields.

The type field specifies the type of data stored in the atom and, by implication, the format of that data. In

some cases, the size and type fields are followed by a version field and a flags field. An atom with these

version and flags fields is sometimes called a full atom.

Note: An atom, as described in this document, is functionally identical to a box, as described in the ISO

specifications for MPEG-4 and JPEG-2000. An atom that includes version and flags fields is functionally identical

to a full box as defined in those specifications.

Atom types are specified by a 32-bit unsigned integer, typically interpreted as a four-character ASCII code.

Apple, Inc. reserves all four-character codes consisting entirely of lowercase letters. Unless otherwise stated,

all data in a QuickTime movie is stored in big-endian byte ordering, also known as network byte ordering,

in which the most significant bytes are stored and transmitted first.

Atoms are hierarchical in nature. That is, one atom can contain other atoms, which can contain still others,

and so on. This hierarchy is sometimes described in terms of a parent, children, siblings, grandchildren, and

so on. An atom that contains other atoms is called a container atom. The parent atom is the container atom

exactly one level above a given atom in the hierarchy.

Media Description 19

CHAPTER 1

Overview of QTFF

For example, a movie atom contains several different kinds of atoms, including one track atom for each track

in the movie. The track atoms, in turn, contain one media atom each, along with other atoms that define

other track characteristics. The movie atom is the parent atom of the track atoms. The track atoms are siblings.

The track atoms are parent atoms of the media atoms. The movie atom is not the parent of the media atoms,

because it is more than one layer above them in the hierarchy.

An atom that does not contain other atoms is called a leaf atom, and typically contains data as one or more

fields or tables. Some leaf atoms act as flags or placeholders, however, and contain no data beyond their size

and type fields.

The format of the data stored within a given atom cannot always be determined by the type field of the

atom alone; the type of the parent atom may also be significant. In other words, a given atom type can

contain different kinds of information depending on its parent atom. For example, the profile atom inside a

movie atom contains information about the movie, while the profile atom inside a track atom contains

information about the track. This means that all QuickTime file readers must take into consideration not only

the atom type, but also the atom’s containment hierarchy.

Atom Layout

Figure 1-1 (page 20) shows the layout of a sample atom. Each atom carries its own size and type information

as well as its data. Throughout this document, the name of a container atom (an atom that contains other

atoms, including other container atoms) is printed in a gray box, and the name of a leaf atom (an atom that

contains no other atoms) is printed in a white box. Leaf atoms contain data, usually in the form of tables.

Figure 1-1 A sample atom

Container atom

Atom size

Atom type

Container atom

Leaf atom

Atom size

Atom type

Atom data

Atom size

Atom type

A leaf atom, as shown in Figure 1-1 (page 20), simply contains a series of data fields accessible by offsets.

Atoms within container atoms do not generally have to be in any particular order, unless such an order is

specifically called out in this document. One such example is the handler description atom, which must come

before the data being handled. For example, a media handler description atom must come before a media

information atom, and a data handler description atom must come before a data information atom.

Atoms

CHAPTER 1

Overview of QTFF

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