Review: Telestream Vantage Transcode Multiscreen
Less obvious in the screen shot is the drop-down box in the upper right, which shows that Vantage can also package the streams in DASH and Smooth Streaming formats as well as MPEG4, QuickTime, Y4M, and TIFO (Telestream Intermediate Format) files. To the right of the list are the fields for inserting encryption identifiers and credentials for the HDS files.
This workflow is extremely efficient when outputting into multiple output formats. Assume, for example, that I was outputting my adaptive group of 11 files into three outputs; MP4 files for local and RTMP Dynamic Streaming and packaged output for HLS and HDS. With my 11 test files, Vantage scaled five times, one for each resolution in the group, and encoded 11 times to produce the elementary streams, which it packaged into the respective output targets without re-encoding. In comparison, some competitive products would have to scale and encode 33 times to produce the same outputs.
To add closed captions to the streams, enable a metadata processing filter that detects and parses out the captions and inserts them into compatible streams. Using this feature, I was able to insert closed captions into the HLS and HDS streams.
Despite the packaging efficiencies, performance was underwhelming, though there were some bright spots, and this is a 1.0 product. Table 1 tells the story. I ran three sets of tests on four sets of encoders. I tested the two software encoders, Episode Engine and Harmonic’s ProMedia Carbon, on an HP 3.33GHz 12/24-core (with HTT) Z800 running Windows 7 Professional, while the GPU-accelerated tests were run on current versions of an Elemental Server and Lightspeed.
Table 1. Vantage’s performance tests were underwhelming, with some bright spots. All times are in hour:min:sec.
The first test is a single, 5-minute 1080p file encoded to a 720p preset at 2.4Mbps. Here, Episode Engine, with its highly efficient split-and-stitch technology, was the overall leader, encoding the file in just under 1 minute, even faster than the Elemental Server, the performance leader in the enterprise encoder market.
The second test is encoding a single, 52-minute 1080p file to an 11 stream adaptive group. Here, Episode Engine, encoding solely via the CPUs on the HP Z800, outperformed the Lightspeed encoder that used both GPU and CPU on a system with 33% more CPU cores, albeit at a much slower rate (2.0 GHz compared to the Z800’s 3.33 GHz).
I checked CPU and GPU utilization while running this test on the Lightspeed encoder, and CPU utilization averaged between 30% and 40% while GPU was between 50% and 60%. This likely means that Telestream will be able to speed performance by improving CPU/GPU utilization during this type of operation. It’ll certainly have to do just that to come anywhere close to the performance of the Elemental Server.
The final test involves encoding 24 1-minute DV files to the same 11 file adaptive group. Here the Lightspeed engine performed at its best, pretty much halving the encoding time of Episode Pro and nearly matching the time posted by Elemental Server. Not surprisingly, in this test, Lightspeed’s CPU averaged consistently above 90%, with the two GPUs averaging between 75% and 98% utilization.
Overall, if you’re encoding long files into multiple adaptive streaming packaging, you’ll find Lightspeed’s 1.0 performance unimpressive. If your encoding chores involve multiple shorter files, you’ll find it much more to your liking.
To test stream quality, I compared Lightspeed to the output quality of Elemental Server. I ran two sets of quality-related tests, the first at 720p at 800Kbps and the second at 640x360 at 240Kbps. To put the first test in perspective, ESPN encodes its 720p streams at 2.8Mbps, which is very close to the same rate as YouTube, both more than three times the tested data rate. Why test so low? At this resolution, there’s probably little justification, except that at 2.8Mbps, all encoders look great.
At the 720p at 800Kbps configuration, the quality was very close, though Vantage retained slightly more detail than Elemental, as shown in Figure 6. Clearly, however, without these types of side-by-side comparisons, which are never available in the real world, no viewer would notice the difference.
Figure 6. Slight advantage to Vantage in this 720p test at 800 Kbps
The second comparison, at 640x360 at 240Kbps, represents the low end of an adaptive group of files actually used by a three-letter network today. Though a very aggressive configuration, it is realistic. Here, though the quality differences between Elemental and Vantage were slightly more apparent, their origin is a bit in question.
To explain, I produced the 720p comparison using two-pass VBR but the 640x360 comparison using CBR, because that file was part of an adaptive group, and CBR is recommended for adaptive streaming. Before comparing the files, I tested the flatness of the CBR stream in Bitrate Viewer, and you can see the comparisons in Figure 7. Specifically, on top, the Vantage stream was clearly lower during the low-motion sequences at the start of my test clip and higher toward the back, so more bits were allocated toward the high-motion sequences in the second half of the clip. In contrast, the Elemental stream, on the bottom, was perfectly flat throughout, which mean less data allocated to the high-motion clips at the back of the stream.
Figure 7. Elemental produced a flatter, more consistent CBR stream.
In my quality comparisons, the low-motion scenes at the front of the clip looked identical, with a very slight advantage for Vantage in the higher-motion sequences toward the back. Since this could have been attributable to the data rate advantage that Vantage enjoyed over Elemental during this portion of the clip, it’s not an apples-to-apples comparison, and I can’t call Vantage the quality winner.
Though the use of interlaced source is waning, it’s still out there, and deinterlacing quality can make or break overall quality. To test deinterlacing quality, I used a 4:3 interlaced DV test file containing nine scenes, each with high motion, sharp edges, or fine detail that complicates effective deinterlacing. With each tested encoder, I rendered the DV source file to 640x480 progressive using the H.264 codec at 10Mbps, high enough to ensure the absence of compression-related artifacts.
For this test, I compared Vantage to Elemental and two popular desktop encoders that shall remain anonymous. Running Vantage in the Automatic mode that most producers would use, deinterlacing quality was very, very good, though a touch behind Elemental in some of the harder scenes. In other scenes, however, the Vantage output was superior to Elemental, and both the GPU-accelerated products left the desktop products in the dust in these comparisons. This bodes well for interlaced source footage produced to streaming formats by the Multiscreen software.
Data Rate Accuracy
The area where Vantage performed the worst was in data rate accuracy, which I tested by comparing the actual output data rate in my group of 11 adaptive files to the specified data rate in the encoding settings. Here, Vantage was all over the map, for example, producing a 2.116Mbps file rather than the requested 2.4Mbps and 1.137Mbps rather than the requested 1.2Mbps. Fortunately, this is a simple problem to resolve; just check the encoded data rate after your first set of encodes and adjust as necessary to produce the desired rate.
Where does this leave us? The biggest attraction of the Vantage system is the workflows it enables. The new Multiscreen encoder works within these workflows and extends them to incorporate new adaptive outputs such as HDS and HLS. If you’re already sold on Vantage and are distributing ABR files, Multiscreen is a natural, though there is clear room for improvement on several fronts, including performance, CBR, and data rate accuracy. On the other hand, if you’re looking for the fastest encoder in the land, Vantage Lightspeed clearly isn’t it, particularly for longer source files.
This article appears in the April/May 2013 issue of Streaming Media magazine as "Review: Telestream Vantage Transcode Multiscreen."
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