买家指南:基于云的视频编码和转码2015
一般来说，主要的SaaS供应商，编码.com和 Zencoder在我的试验中表现相似. 亚马逊的Elastic Transcoder花了两倍多的时间, making it a poor choice for companies requiring the absolute fastest encoding time. 另一个极端是QuickFire.电视异常快。, finishing all encoding in less than 20 percent of the time required by the second-fastest encoder.
Obviously, performance matters if you’re racing to publish time-sensitive content. 另一方面, 对于大多数其他编码工作, the difference between an encoding time of 20 minutes and 2 hours might not be that significant.
费用是多少??
Pricing model and cost are where you’ll find the most significant differences between the cloud offerings. 不幸的是, you’ll have to work very hard to gather useful comparative data on these points for multiple reasons. 第一个, there’s a big difference in pricing between Elemental’s PaaS model, 价格取决于预留的cpu, 以及基于使用情况的SaaS模式. 第二个, 一些SaaS提供商按编码分钟收费(Zencoder), 亚马逊)，而其他人则按GB进出收费(编码.com, Heywatch).
第三，许多供应商都有自己的定价调整. 例如, Zencoder charges 25 percent of the normal cost for files produced via transmuxing, 所以你会付全价买mp4, but only 25 percent of that price for the MP4s converted into HLS or HDS. 编码.com offers some premium price levels for higher performance, and QuickFire.TV基于编码时间和质量提供了三种定价模式. 所有供应商根据每月承诺调整价格, 如果你足够大, I’m guessing most vendors would throw the price list out and negotiate from scratch.
全面估计价格, you’ll have to quantify the number of files you’ll encode each month, 他们的时间, 输入的大小, 输出的大小, 你多快需要这些文件, 以及你对这些数量的承诺有多坚定. You can get a long way using the price schedules most vendors supply, 而是为了获得你可以依靠的信息, 你应该和销售代表核实一下这些数字.
测试，测试，再测试
大多数云提供商提供了合理数量的测试编码, which you should use to ensure compatibility with your existing workflows. Compatibility shouldn’t be a problem, but you never know for sure unless you test.
Now let’s turn our attention to choosing a cloud encoder for live production.
实时云转码
A live cloud transcoder inputs a single live signal and transcodes that signal into multiple files. So, 你可以传输一个720p, 5Mbps流到云端, which the transcoder converts to six separate streams for adaptive delivery. 转码后, the cloud transcoder can transmux the streams into different container formats for delivery to multiple platforms, 例如针对iOS设备的HTTP 在线直播 (HLS), and HTTP Dynamic Streaming (HDS) for delivery to Flash-based desktops and notebooks.
实时云转码有两个关键的好处. 第一个, 因为你只在现场创建一个流, 你可以使用一个非常便宜的实时编码器. 第二个, again because you’re only sending a single stream to the cloud for transcoding, 您的出站带宽需求最小. 使用实时云转码, you can provide an adaptive live experience where it wouldn’t be possible if you were encoding onsite. These two benefits make live cloud transcoding beneficial to virtually all live event producers who haven’t already invested in an expensive multiple stream encoder and the bandwidth necessary to push the encoded streams into the cloud.
再次从清单开始
如你所料, most of the relevant questions asked of live encoder candidates are similar, 如果不完全相同, 到那些你会问VOD提供商的问题. 首先列出所需的格式以及输入和输出点, and make sure the live service provider can check all the relevant boxes. DRM、字幕和其他附加内容也是如此. If your existing on-prem or VOD cloud provider has a live service offering, check that out as well; it’s usually simplest to work with one company than two.
You have the same roll-your-own option as described above with the Wowza代码转换器, 哪些可以部署在各种云平台上, 包括亚马逊EC2, Rackspace, 和微软Azure. 您还可以从几个SaaS提供商中进行选择, 最著名的是Zencoder, 哪个是该领域的先行者, 和元素, which was one of the first appliance vendors to move to the cloud.
Interfaces vary by service provider; some are scripting only, 而另一些则提供传统的用户界面. 与VOD云编码器一样, be sure to choose a provider with an interface that matches your technical capabilities.
虽然我还没有测试过实时转码的质量, I would expect it to be relatively uniform among the service providers for reasons described above. Performance should not be an issue; the providers can either create the required number of streams or not. 不同的供应商定价不同, though there’s a great deal more uniformity than with VOD providers.
服务才是关键
Service is a huge differentiator, since if your live transcoder fails, so does your event. Make sure the provider offers live telephone support during the hours you’ll be broadcasting, 确定成本, 并询问是否有任何与服务相关的保证. I would also check if the provider offers a free test broadcast; if not, produce a test anyway. You never should go live with a new provider on a mission-critical event without completing a live run-through first.
This article appears in the 2015 流媒体源手册 as "Cloud-Based Video 编码 and Transcoding."
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