2022年2月28日
By 斯蒂芬·莱德尔 Bitmovin联合创始人兼首席执行官
博客

Why HDR Provides the Quality OTT Providers Need to Excel

流媒体视频服务已经表明，你不需要离开家或订阅传统的有线电视服务就能观看优质内容, but the video quality may not be consistent. Viewers certainly expect it to be—that's why they purchase new displays, 提供更高分辨率并支持高动态范围(HDR)的智能手机和平板电脑. 如果一家OTT提供商无法在这个层面上提供流媒体内容，消费者可能会转向其他地方.

从编码到回放, 从SDR转向HDR的组织将极大地提高视频体验质量(QoE)。. HDR is not yet the norm for streaming video, but most new content is being produced with the technology, 这就引出了一个问题:为什么流媒体视频服务不利用这一点? 既然人们已经为OTT提供商支付了高额费用，为什么还要购买蓝光光盘才能以原本的方式观看内容呢? HDR is gradually becoming ubiquitous in the general streaming space, but the industry as a whole must catch up. In other words, OTT 服务 will need to provide HDR content to remain competitive. 流媒体行业分析师丹·雷伯恩认为，HDR将成为一个或多个OTT服务的关键优势预测 that HDR adoption will accelerate significantly over the next two years.

我同意他的评估，但我也会补充说，HDR将是任何采用该技术的流媒体服务的显著区别. But not all technology is created equal, and the same can be said about HDR. Designed to provide superior visuals with a greater variety in brightness, 对比, 色彩准确性, HDR offers a distinct advantage to streaming video. There are four common encoding standards – HDR10, HDR10 +, HLG (hybrid log-gamma) and Dolby Vision – being used to bolster picture quality, but their differences are very important. In order to develop the very best OTT platform possible, it is important to understand these differences. 让我们仔细看看HDR是如何工作的，以及不同版本如何影响流媒体内容的视觉质量.

HDR对色彩的影响

HDR produces darker blacks and brighter whites than standard dynamic range (SDR). It also increases the number of steps between each value of gray, resulting in more shades of that color as well.

在摄影中, HDR图像是由几张照片组合而成的——每张照片在不同的曝光下拍摄，每张照片的光量增加一倍. 在视频, HDR只使用一次曝光，而是依靠与HDR兼容的显示器的力量来确保图像的明亮部分真正明亮，而黑暗部分保持适当的黑暗.

HDR provides a significant improvement in color, 基于绝对红色的值, green and blue levels regardless of the video format. With a greater range for both color as well as 对比, HDR offers impressive illumination with difficult light. 这使得它更容易捕获和更准确地显示包含浅色背景和深色前景的图像的惊人视觉效果.

考虑到这一切，OTT提供商可能会对尽快使用HDR感兴趣. But before they do, they need to review the primary standards currently in use.

HDR的四种类型

There is no one-size-fits-all HDR solution. Each encoding standard requires different hardware and video content, so it’s unlikely that every need will be fulfilled by a single standard. 与其从一堆解决方案中挑选“最好的”，不如让我们专注于每个解决方案所能提供的:

HDR10: 由超高清联盟提出, HDR10遵循了一些值得注意的惯例:它使用了ST2084感知量化(PQ)曲线和REC.2020色彩空间. HDR10 also supports TVs with luminosities of 1,000尼特(与100尼特的SDR电视相比)，同时允许在4的显示器上进行母带,000年尼特 and support for the future up to 10,000年尼特. 这是一个开放的, 免版税的标准, which has allowed its popularity to flourish, offers 10bpc (bits per channel) encoding and uses static metadata. 最后但同样重要的, HDR10 can be found in virtually any TV that supports HDR, 从昂贵的高端电视机到廉价的显示器, 提供广泛的消费者范围.

HDR10 +: Much like the "plus" added to any number of products, 服务, 解决方案, 和标准, HDR10 + is essentially an enhanced version of HDR10. 通过提高图像质量和添加额外数据层的选项(目的是逐场景甚至逐帧更新亮度)，hdr10 +提供了一些优势. It also incorporates 动态元数据, 这样可以更有效地进行色调映射，并为每个场景提供单独的信息. 亮度值高达10,000尼特，分辨率高达8K, HDR10 +是一个强大的选择. Display manufacturers appreciate the lower price and freedom compared to Dolby Vision, 我们接下来要讨论什么, as it allows them to bring their own strengths and processes into play.

回龙观: Co-developed by the BBC and NHK for broadcast applications, HLG uses a hybrid approach for its gamma function. It combines the SDR gamma curve with a logarithmic function for the HDR range, 创建了一个两全其美的场景，在这种场景中，可以在SDR和hdr监视器上观看HLG内容. 它还允许一个视频信号同时支持HDR和SDR直播，而无需分级或使用lut.

杜比愿景: 亮度值高达10,000年尼特, 动态元数据, 和12bpc编码, Dolby Vision offers the highest quality HDR available. 与竞争对手的HDR标准相比，杜比视界还能够复制现实生活中的场景和图像，以产生更逼真的日出和其他视觉效果. But it is the most demanding standard currently in the market, 杜比视界则收取内容创作者和设备制造商都必须支付的许可费. If a company can afford to pay for it, the benefits are pretty clear – but it may not be right for everyone.

故事讲述者和设备制造商希望确保他们提供最具视觉吸引力的内容. HDR可以帮助他们实现这一目标, 但在决定使用哪一个标准之前，他们必须首先了解三个主要标准之间的差异. 也就是说, 即使每个人都采用HDR来录制所有新内容，并将旧视频从SDR升级, 质量仍然会有所不同.

有利的一面, 这为流媒体服务提供了另一个机会，通过提供最好的HDR质量来脱颖而出. 我预测OTT提供商迟早会通过接受这项技术而获得成功, and by taking the time to do it right from the start. From price and image quality to freedom and flexibility, there are a number of attributes to consider. OTT提供商应该仔细探索他们的选择，并投资于最适合他们需求的HDR解决方案, as well as the needs of their consumers, while keeping a close eye on competitors’ HDR deployments.

[This is a contributed article from Bitmovin. 流媒体 accepts vendor bylines based solely on their value to our readers.]