Worst Case: Bandwidth Savings
Next, I wanted to check performance with
a more challenging clip, so I tested a 5-minute
segment from the movie Zoolander. Table 2
tells the tale. With a data rate throttle of 15Mbps,
QBR saved between 18 and 19%, depending
upon mode. With a throttle of 5Mbps, QBR essentially broke even.
Perhaps more concerning was the number
of bitrate changes in the four QBR results. Traditional ABR dogma states that you achieve
the best quality of experience finding the optimal bitrate and staying there, as stream switching is often obvious to viewers. Of course, in a
clip with varying amounts of motion, staying at
the same bitrate would mean slight improvements and degradations in quality as scenes get
more or less complex.
MediaMelon’s assertion is that
these frequent stream changes produce more consistent quality over
the duration of the clip. It’s hard to
argue with that, but if you’re beta
testing the technology, observe the
playback streams and draw your
Checking the Uplift
Next, I wanted to check MediaMelon’s claims that QBR delivers
“complex scenes at higher bitrates
than the average available data
rate, improving perceived quality.”
In essence, I wanted to see if QBR
would look ahead and send smaller
segments of easy-to-encode scenes
in order to later send larger segments of harder-to-encode scenes.
The QBR player tracks this during playback
and calls it “uplift.”
MediaMelon sent a screenshot from one of
its test clips, which showed an uplift of 24.84%
(Figure 4). Using the same clip, with the band-
width throttle set at 4Mbps, I was able to dupli-
cate the results.
As a check against the results achieved with
the MediaMelon clip, I tested with a clip that
mixed 30 seconds of talking head footage with
30 seconds of ballet, thinking that QBR would
send smaller segments during the talking head
sequence and larger during the ballet. Table 3
shows our results at the two test bandwidths.
At 15Mbps, QBR showed 38.8% savings, but no
uplift. Basically, QBR retrieved all talking head
segments at 4.3Mbps, and all ballet segments at
Results from the
ballet test clip
clip showed an
uplift of 24.84%.