评论:HLS的无处不在可能是破折号的收获

Adobe几周前上了新闻，当时它宣布即将被列入苹果的HTTP直播(HLS) 在黄金时段 player, part of Adobe's video publishing ecosystem for big media companies.

是的, 我们都同意, 这对HLS来说是件大事, both from the standpoint of players—all major players, except the standalone Flash Player without the 黄金时段 SDK on top, now have plans to include HLS—as well as a win for Apple in creating a 事实上的标准的专有解决方案.

But it may be too much too late, and could spell the beginning of the end of HLS as we know it. 等等，我是说太少太迟了? No, 在这个例子中, 我认为HLS很受欢迎, as it is thrust out on to the global broadcast stage without yet fully putting on its costume (stabilized "recommendation" spec) may be its undoing.

以下是需要考虑的五点:

HLS不是一个结构化标准

请记住，HLS源自规范, often referred to as the "Pantos spec" that's been through many iterations as an IETF recommendation. 这是一个非常流畅的过程.

HLS实现, 到目前为止, 一直谦卑, 在最好的情况下, for those who follow the specification (any version of the specification). I've heard a number of complaints across the industry, ranging from "the spec doesn't exactly provide the detail we're used to in a standard" to "Apple provides the specification to make it appear like anyone can implement HLS, but we see Apple implement it differently from the spec."

HLS Isn't Even Really MPEG-2 Transport Stream (M2TS)

In its current form, HLS is based on a modified MPEG-2 Transport Stream. 这在两个方面存在问题:首先, when it comes to integrated digital rights management and a number of other key HTTP streaming requirements, true MPEG-2 Transport Streams aren't cut out to handle the load. 第二个, Apple's version of M2TS isn't even in lockstep with the M2TS standard, meaning broadcasters have to modify their traditional transport stream equipment to be able to work with HLS.

If broadcasters are going to go to all that work, it begs the question of whether they'll consider going to 破折号, which can handle both classic M2TS and the newer, more capable fragmented MP4 file structure with在 M2TS payload.

HLS无法扩展

快速采用HLS, coupled with by-the-specification implementations, are bound to expose several of HLS's primary shortcomings when it comes to mass-scale delivery. There's a reason that Netflix and others deliver via fMP4 to as many devices as possible, 只使用HLS访问iOS设备. 和, 甚至有, a growing number of iOS apps are bypassing HLS altogether, although Apple won't publicly comment on that topic.

开发者现在有了选择

With HLS and 破折号 both slated to be included in all major players, 没有独立的Flash播放器, 在夏天结束之前, 开发商现在有了选择. 他们可以从HLS开始, 但很容易切换到破折号, 考虑到所有主要服务器(AMS 5, Wowza, 等)现在有HLS和破折号支持.

苹果有个选择

One key point in Adobe's 黄金时段 announcement was the fact that 黄金时段 Player will include 破折号, 适用于除iOS设备外的所有设备. 正如Jan Ozer在他的 article 关于黄金时段, "破折号 in 黄金时段 Player will will only extend to the desktop and 和roid versions of 黄金时段, not iOS--the 黄金时段 SDK for iOS will only support HLS".

原因是, according to Adobe director of product management for video solutions Ashley Still, is the processing power that will be required—at the client side—to transmultiplex from a stardards-based adaptive bitrate (ABR) technology such as 破折号 to a proprietary ABR technology such as HLS.

随着三星在世界其他地区的销量上升, 以及苹果销售放缓, the question becomes whether Apple will choose to take an honest look at HLS, 特别是对于大规模交付, and understand the technical issues that point back to fragmented MP4's benefits over HLS.

如果是这样的话, it's an easy enough play for Apple to implement either a standards-compliant MPEG-2 Transport Stream version of 破折号, or to adopt the MP4 file structure for fragmentation. 多么简单? Many readers might not remember that, about a decade ago, Apple championed both the advent of H.264 in streaming and the use of the MP4 file format. 后者不应该让人感到意外, given the fact that the entire MPEG-4 System standard was based on QuickTime, a player capability embedded into every Macintosh, iPad, iPhone and iPod touch—plus a few million Apple TVs.

In conclusion, is it a pipe dream to think that HLS will stumble and falter tomorrow? 是的,可能. Given its antiquated underpinnings, however, it's a matter of when, not if. 实现真正的全球直播, HLS has many limitations inherent to its own design, 苹果很清楚这一点.