<div dir="ltr"><div></div><div>"
there is not a widely accepted standard for evaluating video quality (at least not one of which I’m aware"</div><div><br></div><div>What about ITU-T BT.500? <a href="https://www.itu.int/rec/R-REC-BT.500">https://www.itu.int/rec/R-REC-BT.500</a></div><div>Well, AFAIK, Netflix invented VMAF because ITU methods are very expensive to implement, not automated and PSNR was not good enough.</div><div><br></div><div>"I have no doubt that there exist today and will exist even more so in
the future superior compression that could lower the bitrate needed"</div><div>Yes, 25 Mbit/s is for HEVC (H.265), but the successor H.266 (VVC) is already here and it reduces the data rate required by ~20%, but it seems that Netflix may prefer AV1, which is between HEVC and VVC in terms of performance.<br></div><div><br></div><div>Regards,</div><div><br></div><div>David F.</div><div><br></div><div>
Date: Mon, 6 May 2024 15:22:04 +0000</div>
From: Colin_Higbie <CHigbie1@Higbie.name><br>
To: Nathan Owens <<a href="mailto:nathan@nathan.io" target="_blank">nathan@nathan.io</a>>, Alexandre Petrescu<br>
<<a href="mailto:alexandre.petrescu@gmail.com" target="_blank">alexandre.petrescu@gmail.com</a>><br>
Cc: Frantisek Borsik <<a href="mailto:frantisek.borsik@gmail.com" target="_blank">frantisek.borsik@gmail.com</a>>,<br>
"<a href="mailto:starlink@lists.bufferbloat.net" target="_blank">starlink@lists.bufferbloat.net</a>" <<a href="mailto:starlink@lists.bufferbloat.net" target="_blank">starlink@lists.bufferbloat.net</a>><br>
Subject: Re: [Starlink] It’s the Latency, FCC<br>
Message-ID:<br>
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Nathan,<br>
<br>
While you hit the point in your second paragraph, namely that Apple
REQUIRES 25Mbps (as do others of the major streaming services, including
Netflix today), your first paragraph misses it. It doesn’t matter what
is POSSIBLE (unless you have the ability to persuade all streaming
services to implement those technologies and ensure they work for the
lion’s share of installed end-user equipment and 4K HDR streams, in
which case, well done and I would agree that a lower bitrate is
sufficient). The ONLY factor that matters in terms of required bandwidth
to be considered a fully capable ISP service is what the market demands
for the mainstream Internet services. That is 25Mbps.<br>
<br>
As the article you linked to points out, those lower bitrates are NOT
for 4K HDR (10-bit color depth per pixel). For those, even in the
authors’ chosen examples, and possibly only at 8-bit color (not clear),
the article claims to only get down to a low of about 17Mbps for the
highest quality. I’ve seen other reports that say anything below 20Mbps
will occasionally fail on particular complex scenes that don’t compress
well. Add a little bit of overhead or assume some additional traffic (an
important consideration, given the raison d’être of this group – reduce
latency under load from multiple streams), and you’re back to 25Mbps on
needed bandwidth to support multiple concurrent activities.<br>
<br>
While I concede there is not a widely accepted standard for evaluating
video quality (at least not one of which I’m aware), I dislike that Y
axis (Quality) on their graphs has no metric, especially without a
definition for how they define quality – is it based on lost data, % of
pixels expressing compression artifacts, pixel color drift, or something
else they created for the purpose of making their case? I would say
that NONE of the photos shown constitute a good or excellent quality
level, where all show significant compression artifacts at the
high-contrast boundaries. These are distinct from natural focal problems
with analog systems that are not contrast-dependent. Further, these all
appear to be relatively static scenes with just a few small moving
objects – the kinds of frames and scenes that compress extremely well.
Again, this is why we must look to the market to determine what it
needs, not individual proposals.<br>
<br>
The article also acknowledges that the graph points represent the
average, meaning some frames are better and some are worse. This is bad
because with any lossy compression system, there is a (subjective) “good
enough” level, where values above that don’t add much, but frames that
are worse will stand out as bad. You can’t just watch the average –
you’re forced to also watch the bad frames. In real-world usage, these
will be the frames during high-speed image changes – explosions in
action movies or a fast-panning scene), often the times when preserving
fidelity are most important (e.g., you lose track of the football during
the fast pan downfield, or you really want to see the detail in the
X-wing fighters as the dogfight leads to explosions around them).<br>
<br>
Further, that article is really targeting mobile usage for cellular
bandwidth, where many of these viewing issues are fundamentally
different from the 65” living room TV. The mobile display may offer
120Hz, but showing a movie or show at 30Hz (except for some sports) is
still the standard.<br>
<br>
Now, to be fair, I have no doubt that there exist today and will exist
even more so in the future superior compression that could lower the
bitrate needed at any given resolution and quality level. The one
described in the article could be an important step in that direction.
No doubt Netflix already has multiple economic incentives to reduce
required bandwidth – their own bandwidth costs, which are a substantial %
of their total operating costs, access to customers who can’t get
25Mbps connections, competition from other streaming services if they
can claim that their streams are less affected by what others in the
house are doing or are higher quality at any given bandwidth, etc. As
noted above, however, that is all moot unless all of the major streamers
adopt comparable bandwidth reduction technologies and ALSO that all
major existing home equipment can support it today (i.e., without
requiring people replace their TV’s or STB’s). Absent that, it’s just a
technical novelty that may or may not take hold, like Betamax videotapes
or HD-DVD.<br>
<br>
On the contrary, what we see today is that the major streaming services
REQUIRE users to have 25Mbps connections in order to offer the 4K HDR
streams. Yes, users can lie and may find they can watch most of the 4K
content they wish with only 20Mbps or in some cases 15Mbps connections,
but that’s clearly not a reason why an ISP should say, “We don’t need to
offer 25Mbps for our customers to be able to access any major streaming
service.”<br>
<br>
Cheers,<br>
Colin
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