Buyers' Guide to Per-Title Encoding 2018
Per-title encoding is the generic name for any technology or feature that customizes the encoding ladder of each encoded file to produce the best possible mix of quality and bandwidth efficiency. Per-title encoding is a feature so important that you shouldn’t choose a new encoder or encoding platform that doesn’t have it or have it coming.
We took two hard looks at competitive technologies in 2017, from which we draw most of the observations contained herein. The first was the article “One Title at a Time: Comparing Per-Title Video Encoding Options.” The second was a presentation at Streaming Media West.
This article presents a list of features and operating characteristics to consider when choosing per-title functionality. It concludes with some items to consider when testing any of these technologies.
Technologies and Deployment Models
Per-title technologies come from multiple sources, so job number 1 is identifying a source that matches your encoding workflow. Those who want to acquire per-title encoding with standalone encoder should consider Capella Systems’ Cambria encoder, which includes a source-adaptive bitrate ladder feature. Harmonic also offers the EyeQ content-aware compression ladder on a number of products.
If you’re encoding in the cloud, per-title encoding is available from Brightcove (context-aware encoding), Bitmovin (per-title adaptation), and Microsoft’s Azure platform. You can license encoding technology to incorporate into your own encoding stack from FASTech (intelligent content-adaptive video compression), Beamr (content-adaptive bitrate technology), or EuclidIQ (content-adaptive encoding). Or, you can implement your own per-title encoding function by deploying an encoding technique called capped constant rate factor (CRF), which is used by online video platforms like JW Player.
These are all the technologies we knew about when we wrote this article. If we didn’t mention your technology, we apologies; please contact the author and leave a comment on the web version of this article.
Once you’ve identified the relevant candidates, here are the factors to consider when comparing them.
When we started producing streaming video years ago, constant bitrate (CBR) encoding was recommended to ensure the smooth delivery of video. Since then, many producers have moved to constrained variable bitrate (CVBR) encoding, which targets an average bitrate but allows the bitrate to increase to a specified maximum. For example, with 200 percent CVBR, you might target a 4Mbps average for a 1080p stream but set a maximum of 8Mbps.
Since bitrate control impacts both quality and deliverability; a key issue is whether the per-title technology enables some measure of metered bitrate control. For example, with Capella Systems’ Cambria encoder, per-title is separate from bitrate control, so you can use CBR or CVBR as normal. With other technologies, like capped CRF, bitrate control is integral, so other than setting a cap, you have no control over upward or downward data spikes in the video.
Figure 1 shows Bitrate Viewer analyzing two files, one encoded with CBR on top and the other encoded with capped CRF on the bottom. We’re not suggesting that you use CBR, but if the thought of attempting to deliver the bottom stream makes you break into a sweat, then capped CRF, and other techniques that don’t enable CBR or CVBR, may not be for you.
Figure 1. Capped CRF offers no control over bitrate, which can cause data spikes.
JW Player uses capped CRF in its online video platform, presumably without introducing delivery issues for its customers. Every producer has different views on the importance of bitrate control; make sure you choose a per-title technology that matches yours.
Now let’s take a look at the core features incorporated into most per-title encoding tools.
Core Per-Title Feature Set
At their core, all per-title encoding technologies adjust the data rates of the individual rungs on the encoding ladder upward and downward to optimize quality and bandwidth. However, not all per-title technologies can change the number of rungs in the ladder, or the resolution of those rungs, which is critical for the most efficient operation.
For example, in Table 1 you see two encoding ladders produced by one of the per-title technologies compared at Streaming Media West. On the left is the ladder for the movie Zoolander, on the right is the ladder for a Camtasia-based screencam. The ladder on the left has a much higher top-end rate, but also more rungs, plus rungs at a broader range of resolutions, which is necessary to deliver acceptable-quality movie content to a range of devices connecting over a range of bandwidths.
Table 1. Different content, different encoding ladder
The VMAF scores for each run are shown on the right. (VMAF stands for Video Multimethod Assessment Fusion, which is a quality metric created and used by Netflix.) Note that scores should decrease for the lower rungs, since at these resolutions, the video file loses detail as compared to the 1080p original, as well as possibly showing compression artifacts from the lower data rates.
The Screencam ladder on the right has a much lower top-end bitrate, but since the VMAF value is similar to the Zoolander clip, the quality should be the same. More importantly, because screencams and other synthetic clips like animations retain more quality at higher resolutions, the per-title technology deployed higher resolutions in the top rungs of the ladder and didn’t encode any rung below 800x450 resolution. The per-title technology also cut two streams from the ladder, which makes sense given that the 180Kbps stream is low enough for most connections. This saves both encoding and storage costs.
In our tests, technologies that customized the resolutions in the encoding ladder based on content performed better than those that didn’t. So check for this capability and the ability to drop rungs when not needed in the encoding ladder.
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