network” ( go2sm.com/netflixindex). That said,
if you’re an OTT service distributing over the
internet, you would expect your rates to be similar. Notably, in August, the peak rate reported
by Netflix was 3.99Mbps. In contrast, Akamai’s
Q1 State of the Internet Connectivity report
( go2sm.com/akamaistate) found that the average U.S. bandwidth for 1Q2017 was 18.7Mbps.
Best Case: Bandwidth Tests
Initial tests focused on determining bandwidth savings under ideal conditions, using a
simple talking head video clip retrieved at
15Mbps and then 4Mbps. Figure 3 shows the
results obtained from the MediaMelon player.
On the right, you can see the encoding profile
used. On the top right, you see that the ABR default player would have retrieved 117.56MB compared to 62.24MB retrieved by QBR in quality
mode, a savings of 47.06%.
The graph in the playback window shows the
theoretical ABR retrieval in yellow and the ac-
tual QBR retrieval in blue. In this simple clip,
there was no region where QBR retrieved a
higher bitrate than ABR. For
this reason, there was no “seg-
ment uplift” as detailed in the
figures on the upper right.
I was uncomfortable using
MediaMelon-provided data, so
I used the Charles Web Debugging Proxy to identify the actual segments being retrieved
using QBR in both modes, and
without QBR, and plugged the
data into a Google Sheet. The
Charles Proxy data showed
that at 15Mbps bandwidth, the
ABR player retrieved mostly
Melon’s numbers. In this case, the two QBR
modes actually reduced the number of bitrate
changes during playback of the 2-minute file,
though the differences weren’t significant.
Since the results were nearly identical for
Quality and Bitrate modes at 15Mbps, I only
tested Quality mode at 4Mbps. Here, the ABR
player without QBR retrieved 41.76MB compared to 29. 83 for the QBR player, a savings of
29%. Looking at the fragments in Charles Proxy,
QBR retrieved primarily the 1800Kbps 720p
stream, while the regular ABR player retrieved
the 2.6Mbps 720p stream.
Did MediaMelon make the right decision?
At both data rates, unquestionably yes. To quantify this, I computed the VMAF score for all deployed streams. At 15Mbps, MediaMelon retrieved the 4.2Mbps stream, which had a VMAF
score of 96.07, rather than the 8.1Mbps stream,
with a VMAF score of 97.09. In the 4Mbps tests,
QBR retrieved the 1.8Mbps stream (VMAF=90.88)
rather than the 2.6Mbps
Since it takes 6 VMAF
points to create a single just-noticeable difference, in both cases,
viewers wouldn’t have
Here are my
results for the
talking head clip
data retrieved by