Per-Title Video Encoding: The Time to Get Started Is Now
Let me get straight to the point. Adding a new codec to your encoding mix, whether it’s HEVC, VP9, or AV1, is expensive, time-consuming, and somewhat risky. Adding per-title encoding to your encoding workflow delivers many of the same benefits, but should be much less expensive, much simpler, and much less risky. While all companies should approach codec changes with some level of trepidation, now is the time to embrace per-title encoding, and it’s never been more widely available.
Let me explain. From a streaming media perspective, NAB 2018 will be remembered for the debut of AV1. However, with that debut came some harsh realities, like an encoding cost of at least 10 times more than VP9, and a 2-year delay until decode hardware appears on devices. Although Facebook, Netflix, and You-Tube have all begun AV1 trials, if your streams aren’t viewed by millions, then AV1 makes little sense, at least in the relative short term.
At the same time, HEVC, buoyed by Apple’s inclusion into HLS, is just beginning to see some uptake. Although the benefits are clear, the costs of HEVC are all additive, including significant player development and compatibility testing before implementation and increased encoding and storage costs once you press the Go button.
In contrast, per-title encoding makes your current codec more efficient by creating an optimized encoding ladder for each title. These technologies assess the complexity of the source footage, and can adjust the data rate, the number of streams in the adaptive group, and even their resolution.
Per-title was introduced by Netflix in late 2015, with YouTube announcing its approach in early 2016. The first commercial implementation came in Capella Systems’ Cambria encoder in mid-2016, and now virtually every vendor offers this feature, including cloud vendors Bitmovin, Brightcove, and Mux; encoding vendors AWS Elemental, Harmonic, and NTT Electronics; and optimization vendors Beamr, EuclidIQ, and ZPEG.
The benefits of per-title mimic those of advanced codecs—more efficient streaming and higher QoE. For example, in analyzing the results of their new “shot-based” encoding, which encodes each scene in a video separately, Netflix reported this in a March 9 post on its Tech Blog: “For members with low-bandwidth connections, we will deliver higher quality video at the same (or even lower) bitrate. For members with high-bandwidth connections, we will offer the same great quality at a lower bitrate. Many members will experience less rebuffers and quality drops when there is a drastic reduction in their network throughput.”
One interesting technical note is the difference between per-title encoding, video optimization, and shot-based encoding. When it debuted, Netflix used its per-title encoding analysis as a way to assess the encoding quality of the entire video, and then encoded using two-pass VBR. This is how Cambria’s per-title feature works; the system gauges encoding complexity and then can encode using constant bitrate (CBR) or variable bitrate (VBR).
In contrast, optimization technologies work on a frame-by-frame basis. I’m most familiar with capped CRF and ZPEG, which vary the data rate of the encoded video file according to scene complexity, but Beamr’s and Euclid’s optimization technologies work much the same way. Here, you can’t use a traditional bitrate control technique; in essence, the per-title encoding technology is the bitrate control technique.
If you’re still using CBR because you believe that it delivers the most buffer-resistant experience or broadest playback compatibility, then you’ll probably prefer a traditional per-title technology, at least for adaptive bitrate (ABR) streaming as opposed to downloadable videos. The key question for you when considering any technology is, “Can I apply CBR?” If you’re using 200 percent constrained VBR, then you probably won’t see much additional stream variability from either per-title or optimization.
Shot-based encoding is clearly the future because it presents so many advantages while blowing up many established encoding conventions like fixed GOP sizes and bitrate control techniques. Why not encode each scene using optimized encoding parameters, rather than applying one schema to the entire video? Why not have an I-frame at the start of every scene where it does the most good, rather than every 2 or 3 seconds? Why use a 2-second GOP length for a 3-second scene?
To my knowledge, although shot-based encoding is being worked on, it’s not available from any encoding vendor today. Don’t wait for it, though. Per-title or optimization is here now, and should be on the 2018 to-do list of all encoding professionals.
[This article appears in the June 2018 issue of Streaming Media magazine as "Per-Title Encoding: The Time Is Now."]
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