BBC Talks Resilient Cloud-Based Broadcast System
“我们平均每天收到700万次BBC iPlayer播放请求, our catch-up video service,” said Stephen Godwin, senior technical architect at the BBC, today at Streaming Media West. “That accounts for about 2 percent of the total BBC consumption.”
戈德温在一个名为“BBC如何在云端建立一个有弹性的广播等级系统”的会议上发表了讲话,，戈德温指出，BBC iPlayer是美国最大的视频点播服务.K. He noted that last year the BBC iPlayer served 36.5 billion minutes of content.
戈德温说:“BBC在网上提供的大多数视频内容只在英国提供。. “But it is very popular.”
Depending on exact rights, content is available for streaming for between 7-45 days, on almost 1000 devices. The device types include PCs, iOS, Android, WindowsPhone, smart TVs, 机顶盒——在安卓和iOS设备上都可以流媒体和下载.
“我们还允许在iOS和Android平台上下载长达30天的内容, so you can watch it anywhere,” said Godwin.
With the popularity of iPlayer, BBC发现自己面临着一个挑战，那就是创建一个新的、更好的摄取和转码工作流系统. The new system is called Video Factory.
Godwin说:“Video Factory被设计成可以从头开始扩展，并使用云。.
“We wanted something that would scale,” said Godwin. “The system we were replacing was 4-5 years old, and a hardware solution, and we didn’t plan for it to support smartphones. 在旧系统上，我们开始遇到限制，包括存储限制.”
”When we designed the new system, we wanted a system that would scale in capability and price,” said Godwin. “The old system has some single-points-of-failure. 我们希望转向一种模式，在这种模式下，我们拥有广播链的弹性.”
戈德温随后介绍了Video Factory的四个主要直播组件:Mezzanine, Time-Addressable Media Store, Playout Data, and Transcoding.
In the Mezzanine Capture module, 广播级编码器通过SDI使用3Gbps高清，最多可摄取24个通道. 然后，内容通过RTP分块器传递，以创建80 MB的文件. Content is stored at 10 Mbps for SD and 30 Mbps for HD.
For Time-Addressable Media Store, 块连接子模块将所有段聚集在一起以创建一个覆盖整个广播时间段的文件.
“It’s the world’s best PVR,” said Godwin, 注意到可以在一小时或半小时的长时间内提出请求.
在Transcoding模块中，可以使用基于文件的摄取，也可以使用活动摄取逻辑. 两者都通过转码抽象层发送到基于云的编码器.
“At the moment we’re primarily using Elemental Cloud,” said Godwin, 注意到可以使用其他“地面”转码解决方案.
“Why do we just use transcoding in the cloud?” asked Godwin, somewhat rhetorically, 然后再举一个例子，在黄金时段的BBC地区新闻分为19个独立的地方广播.
“这个新闻时段是弹性建筑的完美模式，”他说.
然后，他解释了BBC如何在新闻时段结束前启动转码实例. The elastic approach, according to Godwin, 这意味着他们能够将直播到点播的时间缩短到大约20分钟. 这与过去在旧系统上使用本地转码器需要8-10小时的时间框架形成鲜明对比.
Video Factory总共基于20个组件，使用Amazon的简单队列服务(SQS)完全由消息驱动。.
“面向消息的架构已经存在了十多年,” said Godwin, “and it is very well understood.”
In terms of deployment, 戈德温说，视频工厂的软件开发大约在一年前正式开始, with the old system being turned off in September. He noted that they used 18 developers over the year’s time, 它已经运行了两个多月了.
“We deployed the transcode abstraction layer first,” he added. 格拉斯顿伯里音乐节是第一次大测试，有170多个小时的视频可供使用. We then built the mezzanine system and deployed that, 这是我们捕捉任何广播内容的安全网.”
Godwin then said rollout continued via various modules, 同时运行少量代码以降低风险，并提供一种简单的回滚方法.
“What do we get?” said Godwin, referring to Video Factory benefits. “More video content is available online, we get faster delivery of live programmes, 我们现在可以做iPlayer首演，剧集在播出前七天就可以在线观看.”
BBC三台最近就采用了这种首映方式.
“What if you watch content before it appears on TV?” an announcer asks on video that Godwin played. “We want to make it the best TV service in the world.”
戈德温为直播电视观众和在线观看iPlayer首映式的观众之间的比较设定了一个基准. For BBC Three, Godwin said a programme with 1.500万观众被认为是一个相当不错的观众收视水平.
“最近的一部剧，在播出前的第一集，我们得到了1分.5 million video requests,” said Godwin. “In some of the later episodes in one series, 我们有时会在节目播出前收到200万的视频请求.”
另外一个好处是可以使用iPlayer播放独家内容.
“We also sometimes have more content than we can broadcast,” said Godwin, using Glastonbury as an example. “所以我们现在提供iPlayer独家服务，只在网上提供一些格拉斯顿伯里音乐节的内容.”
最后，Godwin讨论了Video Factory可能的其他增强功能.
戈德温说:“我们目前的联播系统非常老旧，无法处理高清. “我们还希望将视频工厂与我们的联播链整合在一起”，这将允许BBC在设备和电视上同时进行直播.
Scroll down to watch Godwin's full presentation:
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