一对多:将直播视频流到多个平台
As recently as two or three years ago, most live streams were distributed by a single service provider like Livestream or Ustream, whether on a page on their websites, 通过您的网站上的嵌入式播放器, or both. With the rise of YouTube Live, Periscope, and particularly Facebook Live, the focus has changed from publishing to a single platform to getting your video on every platform possible. As with all things streaming video related, there are multiple ways to get this done. 本文将介绍最突出的替代方案.
One great thing about most alternatives is that you don’t have to be a technology guru to use them. 理解我将在开头介绍的几个关键概念, 你将会成为一个多平台的流媒体专家.
Before we jump in, 请注意，下面讨论的公司是有代表性的抽样, not an exhaustive list. As you’ll see, many of the products and services are ones I’ve reviewed or discussed in the past. 如果你觉得你的产品或服务应该包括在内, feel free to add it via comment below.
Technology Backgrounder
首先要理解的是从编码器接口的角度来看, there are two ways to connect to services like Facebook Live and YouTube Live: via platform-specific presets or via generic configurable destinations. 我们将要讨论的大多数产品或服务, 如果您使用特定于平台的预设, you choose the preset, log in to the service, and your encoding tool and platform shake hands and exchange all required information.
如果您使用的是通用目标或预设, 您必须手动提供相同的信息, which I show how to do in Figure 1. On the right is the server URL and stream key information provided by Facebook Live; on the left are the corresponding input fields from a generic destination provided by livestreaming service provider Livestream. By way of background, real-time messaging protocol (RTMP), originally developed by Adobe, is the common language spoken by all live-streaming encoding tools and live-streaming services. If you must create a custom preset, 你必须在你的流媒体服务中寻找这些参数, 然后将它们复制粘贴到编码器设置屏幕中. Easy-peasy.
为什么几乎一定要使用通用目标? Because the 600-pound gorilla, Facebook’s Platform Policy Live API, states, “Don’t build apps that enable publishers to simultaneously stream to Facebook and other online streaming services.” So, 如果产品或服务为Facebook Live和YouTube Live提供预设, 它不能让你同时使用两者.
What’s the workaround? Stream to Facebook Live via the Facebook Live preset and to YouTube Live via a generic RTMP preset (or vice versa), 所有产品和服务都支持哪些功能.
现在你知道管道是怎么工作的了, 让我们开始了解本地硬件和软件程序.
On-Premises Hardware and Software
这些是你从直播源运行的设备或程序, 无论是在现场还是在您的现场活动中. 总的来说，这些产品的优点是:
- Cost—You pay for it once, and that’s it.
- Ease of use-与编码器和web服务相比，有一种产品需要学习.
- Security-你的视频少了一项服务, 哪些可能对某些网络和业务很重要.
- Lower latency—Web services that redirect your streams add some latency between the live event and the video seen by your viewers.
- Captioning-这在许多本地编码器中可用，但在少数web服务中可用.
这类产品的主要缺点是出站带宽, particularly for those producing live, off-site events at conferences or stadiums where outbound bandwidth costs are prohibitive. That is, with a web service, you send one stream out to the cloud which is then redirected to multiple web destinations. With on-premises encoders, 你正在向不同的网络目的地发送多个独立的流, which all require their own bandwidth. The other primary disadvantage is CapEx, at least for several of the alternatives discussed below.
On-Site Hardware and Software
最便宜的硬件替代品是 Matrox Monarch HDX这是一种双通道、精装、书本大小的电器，售价1995美元. 该设备提供可选择的3G-SDI或HDMI输入, 并且可以独立存储或流式传输任一频道. 你可以发送一个流到Facebook Live或YouTube Live公开分发, and a higher quality stream to an internal server for internal distribution inside the firewall. Or you can stream live using one channel and record a high-quality version for video-on-demand (VOD) upload or editing, 或者从一个输入流到两个目的地.
Prominent features include captioning support and a file-consolidation utility that progressively stores your broadcast to an SD card or USB drive to protect against data loss if the power goes out. The unit also has an SDI bypass that routes the SDI signal through the unit in case of power loss, 因此，您不会丢失预览或其他下游功能.
需要两个以上连接的生产商应该考虑Teradek T-Rax, 可接受多达8个编码器的机架式(2RU)设备, 它们都可以指向不同的服务(Figure 2). This makes it ideal for broadcasters, government agencies, 以及需要直接支持多种服务的大型企业. 高密度显然是该产品的一大优势, as is caption and protocol support, which includes RTMP for livestreaming, and MPEG-TS, Teradek Streaming (TDS) and RTSP/RTP (real-time streaming protocol/real-time transport protocol) for point-to-point transmissions. The unit can also accept decoder cards to decode streams from other compatible encoders, 使其成为远程摄像机的生产来源. The base system with controller costs $1,990, with encoders priced at $1,590, and decoders at $1,490.
If you already own a multi-channel, hardware-based, livestreaming encoder, 您可能可以使用它来流式传输到多个服务, 尽管每个频道的成本将比其他任何一种选择都要高得多. For example, the Telestream光速直播流编码R是一款四通道编码器，售价49,950美元. For the price, however, 你会得到许多额外的功能，比如HEVC输出, full packaging in either DASH or HLS adaptive bitrate formats with caption and DRM support, automated workf lows, 以及在同一台设备上进行流媒体和实时捕捉的能力.
系统可分别输入4路HD-SDI 1080p信号, 或者您可以将输入组合为4K捕获, and can insert stills, animations, and video clips into the live stream. 这使得它成为会议和其他有中场休息的活动的一个很好的选择, 您需要在流中插入石板和其他内容的位置, though you can accomplish this at much less cost with a video mixer and a less expensive encoder. Still, 如果你有一个多通道编码器，像光速直播, 你可能根本不需要购买任何额外的装备.
Desktop Production Software
Desktop production programs can input signals from one or more cameras; add transitions, titles, picture-in-picture, and other special effects; record a master; and stream to an online service. Some programs, like Telestream Wirecast, can stream to multiple locations simultaneously, though not all desktop programs support this.
These software mixers add lots of value to a production at little cost; Wirecast starts at $500 for a software-only version, with turnkey systems starting at $4,995. Wirecast是唯一一款同时在Mac和Windows上运行的桌面混音器, 并与大多数高级服务进行了深度集成. This means simple operation and features like the ability to see the number of viewers and comments while streaming to Facebook Live.
vMix is a popular Windows-only desktop mixer that can also support multiple outputs, although you’ll need the 4K version ($700) to do so. vMix just released vMix Call, 一个简单的方式来输入远程网络摄像头视频, making it a natural for producers seeking an affordable way to produce interviews with remote participants.
Online Options
With online options, you encode one live stream and send it to the service in the cloud. From there, 服务将流重定向到多个输出, which process it just like they would an original stream produced by an onsite encoder. The first benefit of this approach is that it saves bandwidth; so long as you have about 5–10Mbps of outbound bandwidth to reach a single service, 您可以通过任意多的实时服务进行分发. The second is CapEx, as again, you can support multiple live services with a single encoder.
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