Re: [Starlink] It’s the Latency, FCC

["David Fernández" <davidfdzp@gmail.com>]

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" there is not a widely accepted standard for evaluating video quality (at
least not one of which I’m aware"

What about ITU-T BT.500? https://www.itu.int/rec/R-REC-BT.500
Well, AFAIK, Netflix invented VMAF because ITU methods are very expensive
to implement, not automated and PSNR was not good enough.

"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"
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.

Regards,

David F.

Date: Mon, 6 May 2024 15:22:04 +0000
From: Colin_Higbie <CHigbie1@Higbie.name>
To: Nathan Owens <nathan@nathan.io>, Alexandre Petrescu
        <alexandre.petrescu@gmail.com>
Cc: Frantisek Borsik <frantisek.borsik@gmail.com>,
        "starlink@lists.bufferbloat.net" <starlink@lists.bufferbloat.net>
Subject: Re: [Starlink] It’s the Latency, FCC
Message-ID:
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>

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Nathan,

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.

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.

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.

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).

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.

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.

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.”

Cheers,
Colin

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