Review: Harmonic ProMedia Xpress
The Harmonic, Inc. Workflow System (WFS; created by Rhozet, which is now a part of Harmonic) is an architecture for retrieving and encoding audio and video files into multiple single file and adaptive formats, checking their quality, and delivering the encoded results to local or remote destinations. The primary encoding engine has been ProMedia Carbon (formerly Carbon Coder), a Swiss army knife program with extensive input and output options, excellent output quality, and many other fine features. Unfortunately, encoding speed was not one of them.
To remedy this, Harmonic recently released ProMedia Xpress, a highly focused product designed to fit neatly into the encoding workflows used by many broadcasters. Specifically, in its first iteration, the product can only input MPEG-2 transport streams using either the MPEG-2 or H.264 codec, and it can only output H.264 encoded MPEG-2 transport streams, though with additional licenses, the system can convert these outputs into chunked video files and metadata for HTTP Live Streaming (HLS), HTTP Dynamic Streaming (HDS), and Smooth Streaming.
While future Xpress versions will support additional file inputs such as AVI, MOV, and MFX input, including both ProRes and Avid DNx HD, output support will continue to be limited. For example, 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, which is the unit I tested, costs $25,000. The license for each additional adaptive streaming package format is $2,500, with an additional license of $2,500 for encryption for each adaptive format.
The 5200 is a beast of a system, with two computers. One serves as the controller; the other serves as the encoding node. Both are equipped with two 6-core 3.33 GHz Intel Xeon X5680 processors (24 cores with HTT) with 12GB of RAM, and run Windows Server 2008 RT Standard, SP1. The system does not use GPU acceleration, and both units are equipped with a Matrox G200eW graphics card.
The technology that Harmonic developed to speed encoding is called MicroGrid parallel-computing, which, according to the marketing materials, “splits the large H.264 transcoding job into thousands of tiny ones, each of which is completed concurrently, removing the bottlenecks associated with traditional transcoding architectures.” Xpress can operate stand-alone, or it can serve as an encoding engine within the Harmonic Workflow System, operating via a GUI or API. When you drive the system directly, you use the ProMedia Xpress software and its components, which run exactly like the Harmonic WFS.
Building a Workflow
Figure 1 shows the Xpress Manager. As you can see, tabs atop the interface provide details regarding active jobs, queued jobs, pending QC jobs, and other functions. By way of background, all encodings are driven by a workflow, whether started manually, via watch folder or API.
Figure 1. The ProMedia Xpress Manager.
You build a workflow in the Workflow Editor, which uses encoding presets created in the Preset Editor and Packaging presets built in the Package Preset Editor. Figure 2 shows the Preset Editor, where you configure your adaptive streams and set your H.264 encoding options. Configuration options are very limited, including H.264 configuration options. For example, all encoding is single-pass, with constant bitrate (CBR) and average bitrate control options, but not true variable bitrate (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, or even 2-pass CBR, often delivers. You can get this if you incorporate Carbon Coder into the system but at a significant cost of encoding speed. There will be more on quality later.
Figure 2. The Preset Editor: Note that I’m editing the H.264 adaptive group that I deploy in the next screen.
H.264 configuration options are limited to Profile and B-frame interval, without control over options such as entropy encoding or search functions. In truth, for most users, fine control over H.264 encoding options is unnecessary; however, if you know what you’re doing, you may find this lack of control frustrating.
The Package Editor performs a similar function, allowing users to configure HLS, HDS, and Smooth Streaming options such as chunk size and closed caption options. The Xpress packagers can integrate captions from multiple sources, including CEA-608 and CEA-708, DVB Subtitle, and Teletext, and convert the input for use in all three packaged formats, though some custom development may be necessary for complete integration.
Once you have your presets and packages configured, you build them into a workflow in the Workflow Editor, shown in Figure 3. There are three major classes of components (Pre-Transform Tasks, Transform Tasks, and Job End Tasks), with success and failure components available at each level. You see this in the tree-like structure shown in the middle of Figure 3.
Figure 3. The Workflow Editor
Pre-Transform Tasks include quality control or file configuration checks that require the Harmonic quality control service (not included), or notification tasks. Transform tasks are the primary encoding functions that are driven by presets. In Figure 3, you see that I’m deploying the preset created in Figure 2. Upon a successful encode of the source file to this preset, Xpress deploys the HLS and HDS packages. The 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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