2013年7月3日
By 1月时特约编辑
专题文章

回顾:Harmonic ProMedia express

的谐波公司. Workflow System (WFS; created by Rhozet, 哪一个 is now a part of Harmonic) is an architecture for retrieving and encoding audio and video files into multiple single file and adaptive formats, 检查质量, and delivering the encoded results to local or remote destinations. 的 primary encoding engine has been ProMedia Carbon (formerly Carbon Coder), a Swiss army knife program with extensive input and output options, 优秀的输出质量, 还有很多其他的特点. 不幸的是，编码速度不是其中之一.

为了解决这个问题, Harmonic最近发布了ProMedia Xpress, a highly focused product designed to fit neatly into the encoding workflows used by many broadcasters. 具体地说, 在第一次迭代中, the product can only input MPEG-2 transport streams using either the MPEG-2 or H.264编解码器，只能输出H.264编码的MPEG-2传输流, 尽管有额外的许可证, the system can convert these outputs into chunked video files and metadata for HTTP 在线直播 (HLS), HTTP动态流(HDS), 流动顺畅.

While future Xpress versions will support additional file inputs such as AVI, MOV, 和MFX输入, 包括ProRes和Avid DNx HD, 产出支持将继续有限. 例如, though DASH support is scheduled for the next software release, the development path does not include single or multiple MP4 file output; if you’re an RTMP streamer, either use ProMedia Carbon or find another solution.

You can purchase the software-only version of Xpress for $9,000; a rack-mounted turnkey system called the ProMedia 5200 application server, 哪个是我测试的单元, 花费25美元,000. 的 license for each additional adaptive streaming package format is $2,500, 外加2美元的授权费,每个自适应格式的加密值为500.

的 5200 is a beast of a system, with two computers. One serves as the controller; the other serves as the encoding node. 两者都配备了两个6核3.33 GHz Intel Xeon X5680 processors (24 cores with HTT) with 12GB of RAM, 并运行Windows Server 2008 RT Standard, SP1. 系统不支持GPU加速, and both units are equipped with a Matrox G200eW graphics card.

的 technology that Harmonic developed to speed encoding is called MicroGrid parallel-computing, 哪一个, 根据营销材料, 把大H分开.264的转码工作变成成千上万个小的, 每一个都是并发完成的, removing the bottlenecks associated with traditional transcoding architectures.“Xpress可以独立运行, or it can serve as an encoding engine within the Harmonic Workflow System, 通过GUI或API操作. 当你直接驱动系统时, you use the ProMedia Xpress software and its components, 运行方式和谐波WFS一模一样.

构建工作流

图1 显示了Xpress管理器. 如你所见, tabs atop the interface provide details regarding active jobs, 排队的工作, 待处理的QC工作, 以及其他函数. 顺便说一下背景, 所有编码都是由工作流驱动的, 是否手动启动, 通过观察文件夹或API.

图1. ProMedia express Manager.

在“工作流编辑器”中构建工作流, 哪一个 uses encoding presets created in the Preset Editor and Packaging presets built in the Package Preset Editor. 图2 shows the Preset Editor, where you configure your adaptive streams and set your H.264编码选项. Configuration options are very limited, including H.264配置选项. 例如, 所有编码都是单次通过, with constant bitrate (CBR) and average bitrate control options, 但不是真可变比特率(VBR). This enforces the most conservative theories of adaptive streaming, but it may be too inflexible for some producers who seek the additional quality that VBR, 甚至两步CBR, 通常提供. You can get this if you incorporate Carbon Coder into the system but at a significant cost of encoding speed. 稍后会有更多关于质量的内容.

图2. 预设编辑器:请注意，我正在编辑H.264 adaptive group that I deploy in the next screen.

H.264配置选项 are limited to Profile and B-frame interval, without control over options such as entropy encoding or search functions. 事实上，对于大多数用户来说，很好地控制H.264编码选项 is unnecessary; however, 如果你知道自己在做什么, 你可能会觉得这种缺乏控制令人沮丧.

包编辑器执行类似的功能, 允许用户配置HLS, HDS, 流动顺畅 options such as chunk size and closed caption options. 的 Xpress packagers can integrate captions from multiple sources, 包括CEA-608和CEA-708, DVB副标题, 和电子文本, and convert the input for use in all three packaged formats, though some custom development may be necessary for complete integration.

一旦你有你的预设和包配置, you build them into a workflow in the Workflow Editor, 如图3所示. 的re are three major classes of components (Pre-转换任务, 转换任务, 和作业结束任务), with success and failure components available at each level. You see this in the tree-like structure shown in the middle of 图3.

图3. 工作流编辑器

Pre-转换任务 include quality control or file configuration checks that require the Harmonic quality control service (not included), 或者通知任务. Transform tasks are the primary encoding functions that are driven by presets. In 图3, you see that I’m deploying the preset created in 图2. Upon a successful encode of the source file to this preset, Xpress deploys the HLS and HDS packages. 的 packagers input the MPEG-2 transport streams created during the initial encode and create the unique container formats and metadata files necessary for each adaptive format. Since no additional transcoding takes place, these operations are very fast.

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