2013年12月12日
By 1月时特约编辑
专题文章

回顾:Brightcove视频云直播

实时云转码是实时事件流的未来, 现在已经有几家公司提供了, 包括 Brightcove 子公司 Zencoder该公司是最早宣布推出实时转码产品的公司之一. 在这篇综述中, 我将描述该服务是如何工作的, 以及我通过Brightcove的直播服务进行测试的经验, which uses the Zencoder service to transcode incoming streams to multiple iterations and flavors.

短暂的, 实时转码服务接受单个实时流, which it transcodes to multiple streams for adaptive distribution to one or more target groups, 比如Flash和iOS设备. 稍后您将看到有关其工作原理的详细信息. I’m bullish on live transcoding because it solves two key problems faced by most live event producers.

具体地说, most event producers want to serve both high-bandwidth viewers on fast connections and powerful computers and low-bandwidth viewers on smartphones and tablets. 要做到这一点, 事件生成器通常部署自适应流技术, which require multiple live streams configured for different bandwidths and playback platforms. 实际上, 在当今世界, this means producing one set of adaptive streams configured for Flash playback for desktops, 笔记本电脑, 以及更老的安卓设备, and another set of adaptive streams configured for HTTP 在线直播 (HLS) playback for iOS and recent Android devices.

如果你想现场制作这些流, 然而, 你需要一个10美元的硬件编码器,000或更多. 此外，您还需要支持流所需的出站带宽, 可能在8Mbps-10Mbps的范围或更高. Both of these requirements are beyond the reach of many live event producers.

使用实时云转码, 然而, 将单个流发送到转码服务, 哪一个创建了额外的流. You can easily encode the single transmitted stream with a free encoder such as the Adobe Flash Media Live Encoder, 或者像Telestream的无线广播这样便宜的节目, 我在测试中使用的. Transmitting a single stream drops the outbound bandwidth requirements to more reasonable levels. 例如，我使用2.5Mbps输出720p流, which was well within the capabilities of my $49 per month residential internet service. 它也在许多单线和混合4G解决方案的能力之内. 简而言之, live transcoding services allow any streaming producer to produce a high-value experience from anywhere with 4G connectivity or faster with minimal capital expenditure (CAPEX) requirements.

Zencoder服务

Let’s discuss the Zencoder service, then transition over to Brightcove and my testing. 用我在Zencoder联系人的话来说, 它的Live服务是一个“早期产品”, 具有非常基本(但坚实)的功能.” The service is completely API- (application programming interface) driven, with no user interface. 截至10月. 4, 除了Brightcove自己的服务之外, Zencoder可以流到阿卡迈的入口, EdgeCast, 聚光灯下, Amazon CloudFront, Adobe Media服务器, Wowza媒体服务器, 和YouTube Live. 唯一支持的编码器是Wirecast, Flash媒体实时编码器, XSplit, 及开放广播软件(OBS).

Zencoder服务可以输出RTMP和HLS配置的流, 每个输入流可以产生多达20个输出流, 并为现场活动后的点播观看保存了一个版本. Zencoder前50个小时的起价为每小时10美元, 分层定价，1小时后降至每小时4美元,000小时. 计算小时数时包括输入和输出流, 高清输入和输出的成本是正常成本的两倍.

从这个角度来看, 我的测试配置是一个高清流, 两个高清和六个标清, 哪一个1小时的网络直播要花费12小时, 或者最高利率120美元. Note that these are Zencoder’s prices; Brightcove has a completely different pricing structure.

使用Zencoder服务, you have to supply your own server and player and submit encoding requests via Zencoder’s API. 因为我既不是程序员也不是服务器管理员, we decided to test the transcoding functionality by using Brightcove’s Video Cloud Live service, which worked well for us since 流媒体 magazine uses Brightcove to distribute its on-demand video.

Brightcove视频云直播

如果你现在是Brightcove的客户, the value proposition for the Video Cloud Live service is roughly this: You can use all the players and player-related infrastructure, 包括DRM和盈利, 你为Brightcove VOD创建的现场活动, 加上所有的后端分析. 一旦活动结束, the input stream is automatically retranscoded and made available for VOD delivery -- no more uploading a separate file. 除了RTMP和HLS格式的多比特率流之外, Brightcove offers live DVR so viewers can scan through the video at their leisure and return to the live feed at the click of a button.

请注意，您必须是Brightcove的客户才能使用Video Cloud Live. 在这方面, Video Cloud Live isn’t competing with Livestream or Ustream as much as providing a valuable feature for those already using the Brightcove Video Cloud or considering using the service.

Pricing for the new service depends upon the number of streams and their resolution, 还有体积. For $1,700, you get 20 hours of live streaming with a maximum of four SD streams. 不像Zencoder, 20 hours is calculated without reference to the number of streams; it’s the actual duration of the live event. For $4,000, you get 20 hours of streaming with two HD and up to six SD streams. 在这两种计划下，你都有12个月的时间来观看这20个小时的流媒体. Note that these are just the charges to create the streams; normal bandwidth charges apply. These are also the highest possible prices, which drop as your live event volume scales.

Brightcove早在2013年5月就发布了视频云直播, 尽管在很多方面, 你会看到, 这项服务给人一种新生的感觉. 例如, you can’t reach the service through your normal Brightcove Video Cloud login; you have to log in on a separate page. 这不是悲剧, 当然, but it presaged the rough edges I would encounter when actually using the service. Overall, while the plumbing feels very sound, the interface could use some work.

驱赶野兽

Getting started is simple enough, with a simple wizard to drive the workflow. To create an event, you name it, add some metadata and tags, and choose a date and duration (图1). Next you choose a player from live-compatible players existing in your Brightcove account.

图1. 创建事件

然后选择输出选项, 哪些控制输出文件的数量及其配置 (图2). 标准SD配置文件有两个RTMP流和两个HLS流, peaking at 854x480 resolution at 1100Kbps for RTMP delivery and 910Kbps for HLS. 标准的HD配置文件各有四个RTMP/HLS流, RTMP和HLS的峰值都是720p, 2500Kbps. While you can change parameters such as resolution and bitrate and add additional renditions, 你不能调整H.从Brightcove用户界面内部获取264个具体参数. This is probably OK for most users, but it may prove frustrating to those who like to tweak.