MP4技术:ISO媒体文件格式规范

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"ISO Media File format specification MP4 Technology under consideration for ISO/IEC 14496-1:2001/Amd 3" 本文档是关于ISO/IEC JTC1/SC29/WG11,即国际标准化组织/国际电工委员会下属的运动图像专家组(MPEG-4 Systems)的工作文件,详细阐述了ISO Media File Format,特别是针对ISO/IEC 14496-1:2001标准第三修正案(Amendment 3)中的MP4技术规范。 MP4(MPEG-4 Part 14)是一种用于存储数字媒体的容器格式,它允许组合多种数据流,如音频、视频、字幕和交互式内容。这个文件格式的规范旨在促进不同系统之间的多媒体内容交换,并支持多种应用场景。 文档的章节结构如下: 0.1 Base Format 这部分介绍了MP4文件的基础格式,包括文件的基本构成和其兼容性。 0.2 Usage - Interchange: 描述了MP4格式在不同系统和设备间进行多媒体数据交换的用途。 - Content Creation: 关注于内容创作者如何利用MP4格式来创作多媒体作品。 - Preparation for streaming: 阐述了MP4文件如何被优化以适应流式传输。 - Local presentation: 提供了MP4文件在本地播放时的处理方式。 - Streamed presentation: 讨论了MP4在实时流媒体环境中的应用。 0.3 Design principles 这一部分详细阐述了设计MP4格式时遵循的基本原则,这些原则确保了格式的灵活性、可扩展性和高效性。 0.4 Definitions 提供了与MP4文件格式相关的术语和定义,以便读者理解和应用规范。 1 Scope 明确了文档覆盖的范围,包括MP4格式的主要功能和目标。 2 Normative references 列出了规范制定所依据的标准参考文献。 3 Additional references 提供了对理解MP4格式有帮助的额外参考资料。 4 Streaming Support 讨论了MP4格式如何支持流媒体服务,包括: - Handling of Streaming Protocols: 介绍了MP4如何处理各种流媒体协议。 - Protocol ‘hint’ tracks: 解释了如何在MP4文件中添加“提示”轨道以支持流传输。 - Hint Track Format: 描述了提示轨道的具体格式。 5 File organization 深入探讨了MP4文件的组织结构: - Presentation structure: 包括文件结构、对象结构、元数据和媒体数据以及轨道标识。 - Meta-data Structure (Objects): 关注于元数据对象的结构和组成。 文档的其余部分可能继续详细说明文件结构的其他方面,如时间同步、数据类型、编码规则等,以确保MP4文件能在不同环境中正确解析和播放。MP4格式的设计不仅考虑了多媒体内容的存储,还考虑了网络传输、存储效率和未来技术的扩展性,使其成为当今广泛使用的多媒体容器格式之一。

## Problem 7: Is BST Write a function `is_bst`, which takes a Tree `t` and returns `True` if, and only if, `t` is a valid binary search tree, which means that: - Each node has at most two children (a leaf is automatically a valid binary search tree). - The children are valid binary search trees. - For every node, the entries in that node's left child are less than or equal to the label of the node. - For every node, the entries in that node's right child are greater than the label of the node. An example of a BST is: ![bst](pic/bst.png) Note that, if a node has only one child, that child could be considered either the left or right child. You should take this into consideration. Hint: It may be helpful to write helper functions `bst_min` and `bst_max` that return the minimum and maximum, respectively, of a Tree if it is a valid binary search tree. ```python def is_bst(t): """Returns True if the Tree t has the structure of a valid BST. >>> t1 = Tree(6, [Tree(2, [Tree(1), Tree(4)]), Tree(7, [Tree(7), Tree(8)])]) >>> is_bst(t1) True >>> t2 = Tree(8, [Tree(2, [Tree(9), Tree(1)]), Tree(3, [Tree(6)]), Tree(5)]) >>> is_bst(t2) False >>> t3 = Tree(6, [Tree(2, [Tree(4), Tree(1)]), Tree(7, [Tree(7), Tree(8)])]) >>> is_bst(t3) False >>> t4 = Tree(1, [Tree(2, [Tree(3, [Tree(4)])])]) >>> is_bst(t4) True >>> t5 = Tree(1, [Tree(0, [Tree(-1, [Tree(-2)])])]) >>> is_bst(t5) True >>> t6 = Tree(1, [Tree(4, [Tree(2, [Tree(3)])])]) >>> is_bst(t6) True >>> t7 = Tree(2, [Tree(1, [Tree(5)]), Tree(4)]) >>> is_bst(t7) False """ "*** YOUR CODE HERE ***" ``` 。

2023-06-03 上传
2023-05-30 上传

Please revise the paper:Accurate determination of bathymetric data in the shallow water zone over time and space is of increasing significance for navigation safety, monitoring of sea-level uplift, coastal areas management, and marine transportation. Satellite-derived bathymetry (SDB) is widely accepted as an effective alternative to conventional acoustics measurements over coastal areas with high spatial and temporal resolution combined with extensive repetitive coverage. Numerous empirical SDB approaches in previous works are unsuitable for precision bathymetry mapping in various scenarios, owing to the assumption of homogeneous bottom over the whole region, as well as the limitations of constructing global mapping relationships between water depth and blue-green reflectance takes no account of various confounding factors of radiance attenuation such as turbidity. To address the assumption failure of uniform bottom conditions and imperfect consideration of influence factors on the performance of the SDB model, this work proposes a bottom-type adaptive-based SDB approach (BA-SDB) to obtain accurate depth estimation over different sediments. The bottom type can be adaptively segmented by clustering based on bottom reflectance. For each sediment category, a PSO-LightGBM algorithm for depth derivation considering multiple influencing factors is driven to adaptively select the optimal influence factors and model parameters simultaneously. Water turbidity features beyond the traditional impact factors are incorporated in these regression models. Compared with log-ratio, multi-band and classical machine learning methods, the new approach produced the most accurate results with RMSE value is 0.85 m, in terms of different sediments and water depths combined with in-situ observations of airborne laser bathymetry and multi-beam echo sounder.

2023-02-18 上传