是什么 Streaming?
At its most basic level, 流媒体是通过互联网或蜂窝数据网络将音频和视频文件从服务器传送到客户端. The first streaming audio was delivered in 1995, while the first streaming video followed two years later; you can read more about the early history of the technology in the first version of "是什么 Streaming," which we published in 2011. Needless to say, much has changed since then.
What does streaming media look like in 2019? If you’re new to the field, it probably looks like an impenetrable collection of st和ards, 产品, 和 technologies, 事实上, 它是. 但它可以被分解成百家乐软件app最新版下载在定义他们的服务时必须做出的一小部分决定. 本指南确定了这些决定，并向您指出其他内容来帮助您做出这些决定.
Target Streaming Devices
Start by choosing the platforms that you want to deliver video to. 几乎所有的制作人都希望面向电脑和移动设备，但你必须深入挖掘. 例如，您希望在计算机上支持哪些浏览器，以及您希望回溯到多远? 如果你的浏览者在政府或教育机构工作，你可能需要支持Internet Explorer 11或更早版本的浏览器, which means support for legacy formats like Flash. If you’re targeting younger viewers, 闪回退 is likely not an issue.
For mobile, you need to decide between delivering via an app or the browser. 应用程序提供了更多的功能和设计灵活性，但增加了开发成本和时间. Browser support is faster 和 cheaper but offers fewer features (see "Video: Browsers vs. Apps for Content Delivery").
流媒体生产商的下一个主要平台是像Roku这样的OTT (over- top)设备, 苹果电视, Chromecast, 和 Amazon Fire TV. You’ll have to create a channel or the equivalent for each of these devices, 但是它们代表了通过每次开发工作来支持大量观众的机会. If your target viewers are younger, you may also want to support game platforms like PlayStation or Xbox.
最后一组目标平台通常只有最大的流媒体生产商才会采用，那就是智能电视平台. Though t在这里 is some st和ardization through organizations like the SmartTV Alliance (Phillips, LG, Panasonic, Toshiba) or HbbTV, each platform will likely need a separate effort. For an overview on supporting these platforms, 从这个名为“流媒体西部”的工作坊下载讲义Encoding 2018: Codecs & Packaging For PCs, Mobile, & OTT/STB/Smart TVs."
Adaptive Bitrate (ABR) Formats
Each platform identified above supports certain adaptive bitrate (ABR) formats that dictate how the video files are encoded 和 packaged. If you’re distributing video to iOS devices in the Safari browser, 你必须将你的视频打包成HTTP直播(HLS)格式(参见“什么是HLS"). If you’re distributing to Android devices via a browser, Dynamic Adaptive Streaming over HTTP, 或破折号, is preferred (see "What is MPEG DASH"). 如上所述, if you distribute video to mobile devices via apps, you can typically choose whichever ABR format you would like.
对电脑, your format decision will most likely depend upon the off-the-shelf player you select; an excellent starting point for technical readers is this video from Robert Reinhardt at Streaming Media West entitled "Choosing the Best Off-the Shelf Video Player.“所有的OTT机顶盒和智能电视都支持一种或多种格式，除了苹果电视(当然)只支持HLS. 一些较老的游戏平台同样缺乏灵活性，只支持较老的格式，如微软的Smooth Streaming.
最后, to reach their intended viewers, most producers end up supporting at least two formats, HLS和DASH, with a smattering of support for other formats. We’ll discuss how to support multiple formats in the Packaging & Encoding Schema section below.
特性集
Fundamental to adaptive bitrate streaming is the concept that each input file, whether live or video on dem和 (VOD), 编码成一组不同的文件，具有不同的分辨率和比特率，以优化所有观众的播放体验, 无论是通过3G手机还是通过100Mbps宽带连接的4K智能电视观看. The configuration for these different files is called an encoding ladder; the chart below is a suggested encoding ladder from Apple’s HLS Authoring Specification for Apple Devices.
Apple’s suggested encoding ladder from the HLS Authoring Specification for Apple Devices.
Your encoding ladder will change based upon the input of your video, the compression technology that you use, your target platforms, 和 even your geography. Here are two useful videos for creating your encoding ladder—one covering 比特率, 和 one covering 决议. 这里有一些 观察 you can use to fine-tune your encoding ladder.
Digital Rights Management
If you’re distributing sensitive or premium content, you may have to protect it with digital rights management technology, or DRM (在这里’s a useful 底漆 on DRM, while this article describes how Hollywood studios use DRM). As with ABR technologies, different platforms support different DRM technologies. 例如, Chrome 和 Chromecast support Google Widevine; 苹果电视, iOS, 和 MacOS support Apple FairPlay; 和 Edge supports Microsoft PlayReady. 幸运的是, 从技术和管理的角度来看，部署多个drm比听起来要简单.
技术方面，从Flash到HTML5的过渡是由一个叫做 Encrypted Media Extensions (EME) that allows a single file to include multiple DRM technologies. At the same time, 多个供应商为所有相关的drm提供许可，从而简化了商业方面.
关闭字幕
For certain types of videos, closed captions may be 要求, 而对于其他人来说，它们可能是可取的，以达到听障人士或在嘈杂或公共场所播放，这些场所可能听不到声音. You can find a good overview of closed captioning in this article entitled "Closed Captioning for Streaming Media."
Streaming Codecs
编解码器是一种压缩音频和视频的技术，它允许您通过一系列连接将内容传递给观众(参见“什么是编解码器”)," 在这里). Codecs are absolutely critical to streaming video; no codecs, no streaming video.
For about the last ten years, a video codec named H.264 与AAC音频压缩已成为几乎所有流媒体生产商的选择技术. Over the last five years, however, two video codecs, HEVC 和 VP9, 是否已部署以降低带宽成本并在低比特率连接上提高视频质量. This latter point is key; for example, w在这里 H.264 could deliver a high-quality 720p stream at 2 Mbps, HEVC 和 VP9 can deliver a high-quality 1080p stream at the same data rate, which will look better to most viewers. In 2018, a technology called AV1 started shipping, with a technology called Versatile Video Coding to follow in 2020 or so.
Choosing 和 deploying a codec is a complex analysis involving factors like encoding efficiency, platform compatibility, 和 support within an ABR technology. 有关这些考虑因素的概述，请查看流媒体东部的这个视频。”HOW-TO: Comparing AV1, VP9, HEVC & H.264."
Streaming Packaging 和 Encoding Schema
As discussed above, 为了达到所有的目标平台，你可能需要支持多种ABR格式, typically DASH 和 HLS. T在这里 are two approaches; static 和 dynamic packaging.
With static packaging, 您将编码并打包交付这两种ABR格式所需的所有文件，并将它们上传到原始服务器以进行分发. Depending upon how you encode your videos, 这可能会使编码成本翻倍，并且肯定会增加在线存储成本.
The other approach is called dynamic packaging. 在这里，对编码阶梯的所有梯级进行编码，并将其上传到原始服务器. When a viewer clicks on your link, 一个独立的服务器检测玩家需要哪种格式，并自动实时创建所需的包装.
动态打包将存储和编码成本降至最低，但需要一台全天候运行的服务器来打包内容. 通常, 考虑到所有相关成本，动态包装比静态包装便宜, but this varies by application. To learn more about how dynamic packaging works, check out this 入门篇.
At some point in 2020 or so, a technology called the Common Media Application Format (CMAF)将使一组文件同时支持大多数新平台的HLS和DASH, but not all legacy platforms. For producers who can ignore legacy viewers, CMAF将削减与静态包装相关的存储成本，使其成为最实惠的选择.
Content Delivery Networks
Compared to most other forms of web content, 像文本, 图片, 及PDF档案, streaming video is much larger 和 t在这里fore harder to deliver. 出于这个原因, most streaming producers deploy a content delivery network, 或CDN, to deliver their video (See "What is a Content Delivery Network").
Larger organizations may want to deploy multiple CDNs, both for redundancy 和 to optimize delivery in different regions. To learn more about how 和 why to support multiple CDNs, check out the panel discussion from Streaming Media West entitled "CDN Optimization: Working Toward Broadcast Economics & Quality at Scale."
Quality of Service (QoS) 和 Quality of Experience (QoE)
When streaming video is mission-critical to your organization, 衡量你的内容传递的有效性也同样至关重要. T在这里 are two basic technologies 在这里; quality of service (QoS), which measures the technical effectiveness of your video infrastructure, 和 quality of experience (QoE), which measures the actual viewing experience.
While obviously related, the concepts are definitely separate. 例如, if your video packaging is flawed, QoS could be perfect, but the viewing experience would be awful. 出于这个原因, most larger producers use different services to monitor both. For an overview of QoE 和 QoS technologies, check out "Measure it, Improve it: For Video Publishers, QoE 和 QoS are Critical." For a tutorial on how to deploy a QoE technology, check out "How to Measuring Video Encoding QoE ."
在这篇“是什么”指南中，我们向您抛出了许多概念，同时也提供了许多百家乐软件. While this article is just a tip of the big toe into the world of streaming media, if you’ve made it this far you’ve got a great start.
Related Articles
超过100,000 creators use Patreon to run their creative businesses, 和 br和s can tap the platform's enthusiasm 和 resources. Here's how to succeed on Patreon.
11月6日2019
Not sure what to make of the new format on the block? Read this to get up to speed on how HEVC was created, the challenges it now faces, 和 when it will go into everyday use.
2013年2月14日
苹果的HTTP 在线直播 (HLS)协议是用于向iPad和iPhone等苹果设备传输视频的技术. Here's a 底漆 on what HLS is 和 how to use it.
10月14日
A look at what adaptive streaming is, the primary technology providers, 和 the factors you should consider when choosing an adaptive streaming technology
4月28日
A look behind H.264，世界上最流行的视频编解码器，包括编码参数和版税问题
4月4日
A definition 和 history of the content delivery network, as well as a look at the current CDN market l和scape
3月20日
流媒体技术、历史和在线视频市场格局的高级视图
2011年2月26日