珀斯Wijering Talks HLS, DASH, and the JW Player 6
长尾的视频 recently announced the release of JW Player 6这是该公司流行的免费和低成本视频播放器的重大升级. One key new feature is support for Apple HTTP 在线直播 (HLS), which enables desktop computers to play HLS streams, 对于视频发布者来说，通过一组自适应文件来支持桌面和移动观众. 它还提出了关于动态自适应HTTP流(DASH)规范重要性的问题, which was supposed to deliver the same capability, but is not yet available in the marketplace.
We caught up with 珀斯Wijering, the creator of the JW Player, 谁能好心地回答关于JW Player是如何工作的以及它对DASH的潜在影响的问题.
社交媒体: Does the player provide native H.264 playback capability or does it rely on H.264播放由其他模块提供，如Internet Explorer或Safari，或Flash Player?
JW: The player relies on the Adobe Flash plug-in to provide HLS支持 on desktops and on the HTML5
社交媒体: 因此，如果Firefox用户没有安装Flash Player，他们就无法播放HLS(或H.264(一般).
JW: 这是正确的. The browser (or Flash) has to provide support for H.264.
社交媒体: 你曾公开表示Flash的安装基础约为99%. Was that an estimate or do you have actual stats? HTML5的热度如此之高，你认为这一数字为何如此之高?
JW: This is somewhat anecdotal. We see this on our own website, plus analytics providers like Statowl show aggregate breakdowns. 没有Flash的领域几乎都是移动设备.
The Flash Player install base has 总是 been great, and Flash's upgrade cycle is better than ever, with support for auto-updates across Win and Mac, and built-in support in Chrome. 在一些关键的网络用例中，Flash仍然是必需的，其中之一就是流媒体视频. Hulu, 英国广播公司, HBO -- everything is still Flash, for reasons of quality and security, 加上生态系统支持.
社交媒体: 您对浏览器厂商在-à-vis DASH支持方面取得的进展有何感想?
JW: As far as I know, no browser vendor has DASH support on its roadmap. Chrome's work on a Media Source API is the closest to it. 这个API允许发布者使用JavaScript构建自适应流. Chrome会做H.264解码，但解析的清单和比特率的选择是由发行者.
A similar API in Flash allowed JW Player to support HLS. 当它到达时, 我们可能也会利用Chrome媒体源API在HTML5中支持HLS, which means that HLS will play in Chrome without Flash installed.
社交媒体: How do you see DASH support coming into the market? 我听说过插件，然后可能是像Flash Player这样的播放器. 你是这么看的吗? Perhaps through players like yours? 当通用发行商(相对于OTT和其他封闭系统供应商)开始考虑在HTML5中使用DASH时，你有什么感觉?
JW: 现在支持DASH的唯一方法确实是使用Flash插件来构建它. 这很容易做到，就像今天JW Player通过Flash插件支持HLS一样. I think DASH implementations in HTML5 are years out still.
我也看到一些发行商将DASH融入Android、iOS和Windows 8平台的应用中. This is only possible for large publishers though; those that have the dev resources to build and reach to distribute the app. Smaller pubs would be left out.
社交媒体: What's your sense of the pluses and minuses of DASH vs. HLS支持? DASH提供了哪些HLS没有的关键功能(如果有的话)?
JW: The critical feature is DRM. 苹果的HLS提供基于aes128的加密支持，但不提供带有许可的完整DRM. DASH does so, supporting various 协议s (like PlayReady). 幸运的是，在我们的市场细分(SMB)中，DRM不是必需的. 防止热链接更为重要，HLS中的AES提供了这一点.
DASH中还有其他几个HLS曾经错过的功能(如单独的音频/视频片段或外部封闭字幕), but recent versions of the HLS 协议 added many of these in. In a sense, HLS is becoming more and more "DASHy". Maybe Apple is doing this to slowly work towards DASH compatibility? For now, HLS is the only way to stream to iOS devices though.
社交媒体: What's the status of HLS playback on the Android platform?
JW: Officially, Android supports HLS as of Honeycomb. 在实践中, 我们在当前的Android迭代中发现了一些严重的漏洞，这些漏洞会破坏浏览器内的HLS播放:
- On Honeycomb, HLS playback crashes a tablet quite consistently. 不过，这款手机的市场份额只有2%，而且还在萎缩，因此无需担心.
- 在冰淇淋三明治(占26%的份额)上，HLS可以播放，但无法搜索VOD流. The aspect ratio is also not detected, leading to deformed images. 全屏播放时，视频从头开始播放(同样不支持搜索)。.
- On Jelly Bean (3 percent share, 但越来越多的), the aspect ratio issue is fixed but the no-seek issue remains. 另外, the new default browser (Chrome) does not understand HLS, 导致损坏的mime类型检测，并在全屏播放时显示错误消息和流崩溃.
考虑到姜饼(54%的份额)不支持HLS, 在Android上传输HLS的唯一解决方案就是创建自己的应用程序.
社交媒体: What was so difficult about adding HLS支持 to your player? 为什么不早点呢??
JW: 添加HLS意味着我们必须自己对TS流进行解包(解复用), so we had to learn the nitty-gritty details of video containers first. This included all the small differences between providers. Wowza用这种方式设置字节，Akamai用那种方式，Sorenson用另一种方式. 我们必须进行大量的测试和逆向工程，以使我们的HLS支持与所有主要解决方案兼容，并在旧设备上表现良好.
除此之外，发行商过去(现在也是)对RTMP非常满意. The 协议 works quite well, so why change? 只有在今年，我们才真正看到了对HTTP流媒体的需求. The main requirement from publishers for HTTP streaming is 总是 iOS support, which is why we chose HLS over Adobe's HDS.
社交媒体: 你会期待Adobe在不久的将来将HLS播放添加到Flash Player中吗? 如果没有，为什么没有呢?
JW: I don't think Adobe will add this to the Flash Player. HLS是一种由苹果控制的格式，与Adobe自己的HDS格式直接竞争. 与HDS, Adobe is in control of the server, 协议, 和客户端, so it can offer unique functionalities, such as DRM or multicasting. 与HLS, Flash播放器“只是另一个”客户端，Adobe媒体服务器“只是另一个”HLS兼容服务器.
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