买家编码指南2017

The encoding marketplace consists of hundreds of services and thousands of products. It’s not an understatement to say that encoders come in all shapes and sizes, from fluffy cloud-shaped services to hard-edge pico encoders that could probably stop a bullet, 因为它们的组成部分是如此密集地挤在一起.

This 2017 version of the Buyers’ Guide on encoders attempts to capture just a small slice (no pun intended) of what’s needed to make a decision on the best encoder for your particular needs.

建立基线

The very first decision isn’t necessarily about a brand or type of encoder. Rather, 这是一个关于你需要什么作为分辨率基线的决定, bitrate, latency, 以及预期的交付平台.

Most encoders these days are geared toward a sweet spot of one of two high-definition (HD) resolutions—720p (1280 horizontal pixels by 720 vertical pixels) or 1080p (1920 horizontal pixels by 1080 vertical pixels—although some modern encoders are still geared toward standard-definition (SD) resolutions as a way to improve latency and limit delay between initial capture and encoded output.

市场上的一些编码器走向相反的方向, offering the 4K resolution known as ultra HD (UHD) at 3840 horizontal pixels by 2160 vertical pixels. Yes, it’s really equivalent to 2K if you compare it with 720p and 1080p resolutions, 但这就是营销人员为产品命名时发生的事情.

基线比特率可能有点棘手. It’s possible to deliver 720p and 1080p at industry-average bitrates using Advanced Video Coding (AVC), 更广为人知的是H.264.

编码的进展, though, have allowed UHD content—and even some 1080p content—to be delivered at below-average data rates, 由于引入了图像优化和较新的编解码器. 图像优化增强了现有的编解码器，如H.264, choosing which parts of the image to prioritize given the limited computational resources.

较新的编解码器，如高效视频编码(HEVC/H).265)甚至VP9，都比H有一些好处.264, although HEVC has been beset with licensing issues and VP9 has been met with resistance in a marketplace comfortable with H.264编码质量. As a result, VP9是谷歌发布的最后一款VPx产品, which decided to roll The Codec Formerly Known as VP10 into the newer Alliance for Open Media’s AOMedia Video 1 (AV1) codec shortly after Google published initial specifications for VP10.

Given the fact that many media servers can down-sample from one resolution to a lower one, 我们将在今年的转码《百家乐软件》, it’s best to opt for the highest quality you can safely send across your internet connection to the media server.

A good rule of thumb for bandwidth baselines is to send a single bitrate that does not exceed more than 60 percent of your average capacity. 您可以使用DSLReports测试带宽容量.Com或其他类似的多位置测试工具.

延迟是您需要建立的另一个基线, in terms of how long it takes the encoder to convert the input video signal to an encoded stream.

一些流媒体解决方案, such as Apple HTTP Live Streaming (HLS) or an MPEG-DASH HTTP-based delivery, will require upward of 30 seconds from the time of encoding to the time that the encoder is able to send out the first three small-file segments. 在这种情况下，延迟不是编码器的首要要求之一.

If you’re using a media server, though, low latency is potentially achievable. In some cases, a single high-resolution RTMP-based stream can be sent to the media server, which will in turn transcode and package up the segments for HTTP delivery, as well as deliver low-latency streams to those who have a player capable of viewing low-latency RTMP streams.

The trade-off here will be the need to architect the delivery infrastructure to deal with both HTTP and RTMP stream delivery. 正如我们最近讨论的 “Latency Sucks!” article, though, newer technologies such as WebRTC may help strike a balance in terms of latency needs.

Finally, 这是不言而喻的, 您选择的编码器必须能够满足您的目标受众. One reason that Apple’s HLS packaging and segmentation is so popular is that there are hundreds of millions of mobile devices out there that can view HLS-based content, 不仅包括苹果iOS手机和平板电脑, but also smartphones and tablets that use the Android OS mobile operating system.

同样的道理, VP9 and the newer AV1 are key to audiences that primarily use Mozilla Firefox for browsing or, more recently, 我想在YouTube上看4K内容. 2015年年中，YouTube宣布将从H.264支持VP9的4K内容, but it has only been since the beginning of 2017 that some 4K content on YouTube is unavailable in H.264 encoding.

Form Factors

Now that we’ve covered the baseline criteria for your encoding decision making, 让我们来看看编码器最近出现的一些形式因素. Previously, 只有服务器和便携式编码系统可用, 但在过去几年里，情况发生了很大变化.

INTEGRATED

From smartphones and tablets with their built-in cameras up to desktop monitors and ultraportable laptops, a large number of computing devices now come with integrated streaming capabilities.

毕竟，唯一的要求就是一台相机. Many devices now have two—one forward-facing and one on the back of the device—and some form of audio capture. 苹果和惠普最新的笔记本电脑甚至配备了双麦克风, as a way to listen for and potentially eliminate ambient or background noise in a quest to make speech capture that much better.