Let’s start with two observations. First, nothing in video compression is free. With each encoding parameter you adjust, you trade off quality for encoding time, which
translates to cost, compatibility, playability, or
deliverability. To gain in quality, you necessarily
lose somewhere else. There is no magic; optimization is just a series of controlled and (hopefully)
informed decisions about these tradeoffs. Second,
no analysis is ever complete; it’s simply a point-in-time observation of a work in process, hopefully
to advance the overall state of analysis.
You feeling me? If so, let’s begin.
The Challenge: How Low Can You Go?
This article was inspired by an email from editor
Eric Schumacher-Rasmussen, saying, in essence,
that “Netflix and Amazon are now enabling down-
loads, the files are really small but look great. How
are they doing that?” Soon thereafter, Netflix pub-
lished a blog post on its process entitled, “More
Efficient Mobile Encodes for Netflix Downloads”
( go2sm.com/netflixmobile), which laid out its rec-
ipe in general terms. We asked Amazon for similar
guidance, which it declined to provide.
Netflix’s analysis was massive, involving 600
full-length movies or episodes encoded at multiple resolutions on Netflix’s cloud-based rendering
platform, assessed with objective quality metrics,
peak signal-to-noise ratio (PSNR) and video multi-method assessment fusion (VMAF). Using the
techniques discussed in the blog post, Netflix was
able to maintain the same quality of its existing
H.264 starting point while reducing H.264 files
by 15.3% and VP9 files by 35.9% (as measured
Netflix’s mobile download files look terrific.
Here’s how to make your low-bitrate files
look just as good.