Delay Impact on MPEG OMAF's Tile-Based Viewport-Dependent 360° Video Streaming
Delay Impact on MPEG OMAF's Tile-Based Viewport-Dependent 360° Video Streaming
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DOI：
10.1109/jetcas.2019.2899516
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发表时间：
2019-03-01
影响因子：
4.6
通讯作者：
Schierl, Thomas
中科院分区：
文献类型：
--
作者：
de la Fuente, Yago Sanchez;Bhullar, Gurdeep Singh;Schierl, Thomas
随着360度视频流的不断受到关注，最近出现了几种解决方案。它们可以被分成两个主要类别，第一个类别是独立于视点的类别，其包括使用特定投影(例如等角投影或立方图投影)对整个360度视频内容进行编码，而不考虑任何视点方向。这种方法浪费资源，因为未被用户观看的内容被以与实际观看的内容相同的视觉保真度进行编码。第二个类别是依赖于视区的类别，它依赖于允许自适应视区的技术。一种方法是应用依赖于视点的投影，其中球面360度视频以这样一种方式被映射到矩形框上，即特定视区被映射到矩形框中比内容的其余部分相对更大的部分。如在MPEGOMAF中指定的另一种方法是使用基于块的流，其中360度视频以各种分辨率以块的方式提供。因此，每个用户都可以以不同的分辨率检索瓦片，以便高分辨率瓦片与其视区匹配。尽管视窗相关的方法允许在视口处提供更好的视觉质量，但端到端延迟是关键的，因为它会影响客户端适应用户移动以使移动反映在检索到的内容上所需的时间。在本文中，我们分析了延迟的影响，并介绍了各种减小延迟对观测保真度影响的方法。
With the continuously increasing attention that 360 degrees video streaming is drawing, several solutions have been developed lately. They can be grouped into two main categories, with the first one being the viewport-independent category that consists of encoding the whole 360 degrees video content using a particular projection, e.g., Equirectangular Projection or Cubemap Projection, without taking any viewport orientation into account. Such approaches waste resources since content not being watched by the user is encoded with the same visual fidelity as the content actually watched. The second category, the viewport-dependent category, relies on techniques that allow for viewport adaptivity. One approach is to apply viewport-dependent projections, wherein the spherical 360 degrees video is mapped onto a rectangular frame in such a way that a specific viewport is mapped to a comparatively larger part of the rectangular frame than the rest of the content. Another approach, as specified in MPEG OMAF, is to use tile-based streaming, with the 360 degrees video being offered in a tiled manner at various resolutions. Thus, each user can retrieve the tiles at different resolutions so that the high-resolution tiles match its viewport. Although viewport-dependent approaches allow providing better visual quality at the viewport, the end-to-end delay is critical, since it has an impact on the time needed by clients to adapt to user movements so that movements are reflected on the retrieved content. In this paper, we analyze the impact of the delay and introduce various means to reduce the impact on the observed fidelity.