The Player's the Thing...But So Is The Codec, Format, and Protocol

In the beginning, streaming technologies such as Real Media, Windows Media, QuickTime使用实时流协议(RTSP)在服务器和玩家之间进行通信, to provide features such as multiple bitrate files, 更有效地将庞大的视频文件分发给多个播放器. Adobe修改了RTSP以创建实时消息传递协议(RTMP), which provided many of the same functions.

 然而，在2008年的某个时候，RTMP和RTSP在流媒体视频领域变成了四个字母的单词. 这种对RTMP和RTSP的厌恶与通过HTTP发布的推动是一致的, 对于内容分发网络(cdn)来说，哪一个更容易合并, more firewall-friendly, and more cache-efficient. Suddenly, 流媒体视频技术的评估不仅要考虑播放器和编解码器相关的功能，还要考虑可用的传输协议.

In this regard, HTTP re-emerged as the "it" protocol for large event streaming, 备受瞩目的支持者微软从苹果的HTTP Live Streaming声明和Adobe在年底向HTTP投降中获益.

微软也在Flash/Silverlight的战争中取得了一些进展，一些备受瞩目的设计和现场活动的成功, but the installed base remains well below 50%. In the codec market, H.264继续在Flash、iPhone和iPod touch市场获得发展势头——在年中推出了带有H的Silverlight 3.264播放兼容性为基于标准的编解码器在Silverlight市场上的广泛应用奠定了基础.

Still, 谷歌收购On2可能会让VP8在编解码器市场掀起波澜, particularly if Google donates it royalty-free for use with HTML5. At the very least, it will tighten the sphincters of the H.264专利组的一些，使其成员对他们的H.264 monopoly, 特别是如果谷歌打开开关，将YouTube 59%的互联网流媒体份额从Spark/VP6/H转换过来.264 to VP8. Though it’s unlikely that VP8 will be an H.264杀手(甚至更冷)，这比谷歌收购On2之前更有可能.

Finally, the use of multiple bitrate, 自适应流媒体技术是2009年移动网络最强劲的趋势之一, Silverlight, Apple, and Adobe own and promote competing technologies. 2010 could be the year that H.264可扩展视频编码以一些明显的技术优势和基于标准的技术的内在力量进入市场.

This article discusses all of these issues. And for a well-rounded perspective on them, 我与内容所有者/流媒体的多位代表进行了交谈, CDNs, and online video providers (OVP).

Protocols
今年伊始，Move Networks和微软将HTTP推广为大型活动流媒体的最佳协议，而Adobe则坚决支持RTMP. By the end of 2009, Move, Microsoft, Apple, Akamai, and Adobe were all squarely in the HTTP camp, though Adobe’s implementation may not appear until June 2010. While this represents a technological sea change, the implications of the shift for most users will be nominal, at least in the short term. More on that later.

Let’s start with a brief technology description. HTTP是用于从web服务器传递数据的通用协议, whether the data is text, JPEG images, PDF files, or video. RTSP是大多数流媒体服务器支持的行业标准流媒体协议, including Apple’s QuickTime Streaming Server and Microsoft’s Windows Media Services; and RTMP is the proprietary protocol developed by Adobe for Flash. 虽然你可以通过RTSP和多播来传送到Silverlight播放器, most large-scale Silverlight events deliver via HTTP.

与RTSP和RTMP等协议相比，HTTP有几个众所周知的优点. 首先，一些防火墙会阻止RTSP/RTMP数据包，这对防火墙后面的查看者来说是个问题. Second, 基于RTSP/ rtmp的技术通常需要流媒体服务器与播放器进行通信, whereas HTTP-based technologies don’t. This server requirement means that RTSP/RTMP-based technologies are more expensive to implement and maintain; there’s also inherently less RTSP/RTMP capacity than HTTP capacity.

内容交付网络和其他大型网络交付平台的设计和创建是为了交付HTTP内容，因为这种类型的内容构成了互联网上交付的大部分数据. To deliver RTSP or RTMP packets, 这些组织必须安装一个流服务器，使该服务器能够传送这些数据包. In contrast, with HTTP-based streaming technologies, 整个http兼容的基础设施都可以传递这些数据包, which typically means a far greater capacity, or "footprint," for HTTP than RTSP/RTMP.

Third, HTTP data is more cache-friendly than RTMP, 这应该转化为更少的流，以满足相同数量的观众，并为观众从缓存中检索数据提供更好的服务质量. For example, 在公司局域网或通过ISP观看的观看者将从原始服务器检索完整的视频, which would be stored on the corporation’s or ISP’s cache server. 对相同数据的后续请求将从缓存中得到满足, 所以制作人不需要再向CDN支付再次发送流的费用. Since the data is served locally, for all intents and purposes, 随后的观众也应该有更好的观看体验.

HTTP的另一个优点与使用HTTP而不是RTSP的流交换质量有关. 例如，我与美国职业棒球大联盟(MLB)负责多媒体和分销的高级副总裁Joe Inzerillo进行了交谈.com. Inzerillo oversees the streaming of every regular season, postseason, and a few preseason baseball games on the MLB site. I also spoke with Glenn Goldstein, vice president of video technology strategy at MTV Networks, 是什么推动了每月超过4亿的流媒体流量，吸引了超过1300万的独立观众.