3GP与MP4文件格式规范详解

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"3GP和MP4是两种常见的数字媒体文件格式，广泛应用于移动设备和互联网上。3GP主要由3rd Generation Partnership Project (3GPP) 标准化，适用于移动通信系统如GSM、UMTS（第三代移动通信系统）和LTE（长期演进）。该格式设计时考虑了带宽限制和移动设备的存储容量，使得在移动网络上传输视频和音频更加高效。MP4则是MPEG-4 Part 14的简称，是Moving Picture Experts Group (MPEG) 制定的一种多媒体容器格式，它支持多种音视频编码标准，并且在质量和文件大小之间提供了更好的平衡，适合于高清视频和互联网流媒体服务。 3GP文件格式的主要特点： 1. 优化的文件大小：3GP格式通过使用更简单的编码技术和压缩算法，降低了文件大小，适应了3G网络的低带宽环境。 2. 支持多种媒体类型：3GP可以包含音频、视频以及同步文本数据，适用于多媒体消息服务(MMS)和流媒体服务。 3. 快速文件打开：3GP文件头小，使得文件能够快速加载和播放，尤其在移动设备上。 4. 适应性流媒体：3GP格式支持适应性流媒体技术，允许在网络条件变化时动态调整视频质量。 MP4文件格式的主要特点： 1. 高效的编码：MP4采用高效的编码技术如H.264和AAC，提供高质量的音视频体验，同时保持相对较小的文件大小。 2. 多轨支持：MP4文件可以包含多个音视频轨道，以及字幕、互动内容等，适合复杂多媒体应用。 3. 时间线结构：MP4采用基于时间线的结构，便于编辑和操作媒体数据。 4. 网络友好：MP4格式支持网络流传输，适应各种带宽条件，广泛用于在线视频服务。 3GP和MP4之间的转换：由于3GP和MP4在用途和特性上的差异，用户可能需要将文件从一种格式转换为另一种。这通常可以通过使用转换工具或多媒体编辑软件实现，如HandBrake、Format Factory等。转换过程中要注意保持音视频质量，并确保目标设备支持转换后的格式。总结来说，3GP与MP4都是为了满足不同场景需求而设计的媒体文件格式。3GP更适合移动通信环境，而MP4则倾向于提供更高级别的多媒体体验，特别是在高清视频和互联网应用中。了解这两种格式的特点和应用场景，有助于选择合适的文件类型和优化媒体内容的使用。"

ETSI

ETSI TS 126 244 V8.0.0 (200

01)

3GPP TS 26.244 version 8.0.0 Release 8

For the PSS, the 3GPP file format is mandated in [3] to be used for timed text and it should be supported by PSS

servers; 3GP files with streaming-server extensions should be used for storage in streaming servers and the "hint track"

mechanism should be used for the preparation for streaming.

5 Conformance

5.1 General

The 3GPP file format is structurally based on the ISO base media file format defined in [7]. However, the conformance

statement for 3GP files is defined here by addressing constraints and extensions to the ISO base media file format,

registration of codecs, file identification (file extension, brand identifier and MIME type) and profiles. If a 3GP file

contains codecs or functionalities not conforming to this specification they may be ignored, i.e. a 3GP compliant file

parser may ignore non-compliant boxes.

5.2 Definition

5.2.1 Limitations to the ISO base media file format

The following limitation to the ISO base media file format [7] shall apply to a 3GP file:

- compact sample sizes ('stz2') shall not be used for tracks containing H.263, MPEG-4 video, AMR, AMR-WB,

AAC or Timed text.

NOTE: The extended presentation format (see clause 11) is defined by using the Meta box of the ISO base media

file format (second edition) [7] that was not present in the first edition. Hence, extended presentations in

3GP files are explicitly signalled via the Extended-presentation profile (see clause 5.4.6).

5.2.2 Registration of codecs

Code streams for H.263 video [9], MPEG-4 video [10], H.264 (AVC) video [29], AMR narrow-band speech [11], AMR

wide-band speech [12], Extended AMR wide-band audio [21], Enhanced aacPlus audio [23, 24, 25], MPEG-4 AAC

audio [13], and timed text [4] can be included in 3GP files as described in clause 6 of the present document.

5.2.3 Extensions

The following extensions to the ISO base media file format [7] can be used in a 3GP file:

- streaming-server extensions (see clause 7);

- asset information (see clause 8);

- video-buffer information (see clause 9);

- AVC file format (see [20]);

- RTP and RTCP reception hint tracks (see [38]);

- SRTP and SRTCP reception hint tracks with key management information for SRTP recordings (see [38] and

clause 12).

If SDP information is included in a 3GP file, it shall be used as defined by the streaming-server extensions.

5.2.4 MPEG-4 systems specific elements

For the storage of MPEG-4 media specific information in 3GP files, this specification refers to MP4 [14] and the AVC

file format [20], which are also based on the ISO base media file format. However, tracks relative to MPEG-4 system

architectural elements (e.g. BIFS scene description tracks or OD Object descriptors) are optional in 3GP files and shall

be ignored. The inclusion of MPEG-4 media does not imply the usage of MPEG-4 systems architecture. Terminals and

ETSI

ETSI TS 126 244 V8.0.0 (2009

01)

3GPP TS 26.244 version 8.0.0 Release 8

servers are not required to implement any of the specific MPEG-4 system architectural elements.

5.2.5 Template fields

The ISO base media file format [7] defines the concept of template fields that may be used by derived file formats. The

template field 'alternate group' can be used in 3GP files, as defined in clause 7.2. No other template fields are used.

5.2.6 Interpretation of the 3GPP file format

All index numbers used in the 3GPP file format start with the value one rather than zero, in particular 'first-chunk' in

Sample to chunk box, 'sample-number' in Sync sample box and 'shadowed-sample-number', 'sync-sample-number' in

Shadow sync sample box.

5.3 Identification

5.3.1 General

3GP files can be identified using several mechanisms: file extension, MIME types and brands.

5.3.2 File extension

When stored in traditional computer file systems, 3GP files should be given the file extension '.3gp'. Readers should

allow mixed case for the alphabetic characters.

5.3.3 MIME types

The MIME types 'video/3gpp' (for visual or audio/visual content, where visual includes both video and timed text) and

'audio/3gpp' (for purely audio content) shall be used as defined in [27].

5.3.4 Brands

This specification defines several brand identifiers corresponding to the profiles defined in clause 5.4. Brands are

indicated in a file-type box, defined in [7], which shall be present in conforming files. The fields of the file-type box

shall be used as follows:

- Brand: Identifies the "best use" of the file and should match the file extension. For files with extension '.3gp'

and conforming to this specification, the brand shall be one of the profile brands defined in clause 5.4.

- MinorVersion: This identifies the minor version of the brand. For files with brand '3gLZ', where L is a letter

and Z a digit, and conforming to version Z.x.y of this specification, this field takes the value x*256 + y.

- CompatibleBrands: a list of brand identifiers (to the end of the box). Any profile of a 3GP file is declared by

including the corresponding brand from clause 5.4 in this list.

The brand identifier (of one of the profiles) must occur in the compatible-brands list, and may also be the primary

brand. Conformance to more than one profile is indicated by listing the corresponding brands in the compatible-brands

list. If the file is also conformant to earlier releases of this specification, it is recommended that the corresponding

brands ('3gp4', '3gp5', '3gp6' and/or '3gp7') also occur in the compatible-brands list. If, for instance, '3gp4' is not in the

compatible-brands list, then the file will not be processed by a Release 4 reader. Readers should check the compatible-

brands list for the identifiers they recognize, and not rely on the file having a particular primary brand, for maximum

compatibility. Files may be compatible with more than one brand, and have a 'best use' other than this specification, yet

still be compatible with this specification.

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