同时多格式编码

Distributing web content to multiple browsers was once the primary content delivery challenge for streaming media producers. But the proliferation of set-top boxes and mobile devices have added even more complexity to the delivery of video.

Even for content owners who pay a content delivery network (CDN) to deliver to various platforms, the need to understand how to best encode content for these various viewing platforms may be the difference between being a leader and being an also-ran in today’s competitive and increasingly fragmented media environment.

Traditional broadcast 生产 and distribution platforms used a limited range of formats, 例如MPEG-2. But today’s multiplatform world is usually not so consistent. 超越了不断扩大的观看设备的广度, the equal proliferation of 编码 parameters—比特率, 编解码器, and container formats—means that content owners could face significant duplication of effort to push content to every customer.

This article is meant as an introductory-level teaser of sorts. 甚至在单一发行平台上播放, 比如个人电脑上的网络视频, leads to an array of additional considerations and options. 也, 为了介绍一些一般的概念, we’ll overlook a few of the deeper details (for example, metadata handling) and leave those for a separate discussion.

至于术语, for the purposes of this article "编码" will refer to the creation of a live stream or file from a live or tape-based digital or analog video source, and "transcoding" will mean the conversion of file-based media from one container format or codec to another. 同样的, "deliverables" or "delivery" will refer to either live streams or encoded files for subsequent on-demand streaming or progressive download viewing on multiple device platforms. It’s worth nothing that the breadth of compression and file formats used in file-based 生产, 编码, and distribution far exceeds that used for live real-time streaming delivery.

编解码器和容器的融合
One bright spot in all of the complexity that exists around delivery to multiple platforms is the continued convergence of a few key video compression and container formats.

H就是一个例子.264, a video compression standard also called AVC or MPEG-4 Part 10. 虽然H.264 originated as an effort within MPEG-4 development that was intended to replace MPEG-2, H.264 video compression can be used in a variety of container formats, 包括QuickTime MOV, Adobe Flash F4V, and the same Transport Stream wrapper often used for MPEG-2 content.

A container format is often nothing more than a "wrapper" in which compressed video and corresponding encoded audio are delivered to a player application. Some player applications will not play particular container formats, even if the content is encoded with a proper combination of audio and video 编解码器, so simply changing the container format can sometimes allow previously encoded content to be repurposed for use in additional video players. 在某些情况下, 然而, 播放器将支持有限范围的帧大小, 比特率, or even GOP (group of picture) structures within a compression format, 要求内容本身进行转码.

Common technologies for powering web viewing experiences include Microsoft Silverlight, Adobe Flash, 和苹果QuickTime. While each technology supports additional compression formats (for Silverlight, Windows Media and the SMPTE standard VC-1 based on it; for Flash, On2的VP6编解码器最初是在Flash 8中引入的), all three web technologies support video encoded with H.264 compression—providing common ground with current mobile and IPTV platforms. For web-based and newer mobile phone-based interactivity, Adobe Flash or Microsoft Silverlight technologies provide additional interactivity integrated into the video viewing experience.

用于网络和移动观看, the inclusion of adaptive bitrate playback in web-based video players is a welcome addition. 视频源以多个比特率编码, and the players dynamically adapt to variations in consumer bandwidth to provide the optimum viewing bitrate for any given 2–10-second increment. These technologies include Microsoft IIS Smooth Streaming, Adobe动态流媒体, 以及苹果对苹果iPhone的自适应交付.

Each of these targets has its own unique characteristics, and no one set of 编码 specifications comprehensively and optimally serves them all. 适用于任何多平台发行策略, 多格式编码, 决议, 比特率是一个不可避免的需求. 考虑收购的非分销形式, 生产, 和存档, 而可交付成果的种类在几十种之多.

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