[LINK] Propose Video Bandwidth Limit During COVID19 Emergency

[Paul Brooks]

On 20/03/2020 8:34 am, Tom Worthington wrote:
> There is likely to be a high demand for Internet access over the next few months due
> to COVID19. So I suggest that video products be set to limit bandwidth use by
> default. Video streaming and conference tools adjust to the bandwidth available, but
> try to use *all* that bandwidth. This makes them poor online citizens, like someone
> who fills their shopping trolley with toilet paper, if you let them. ;-)

With much respect, I'll take the contrarian view then.

Actually, videoconferencing systems (unlike one-way streaming media like youtube)
don't adjust to use all the bandwidth, and I'm not convinced its a problem these days
except for people forced to use older, slow links.  In a zoom call with ~10 endpoints,
I see sustained downstream bandwidth use under 2 Mbps, only a few percent of the
available link capacity.

Auto-adjusting-quality video streams generally requires the video be pre-recorded and
stored with several different different quality/bandwidth encoding versions of the
whole video file stored in parallel, and the viewing client then selecting the
appropriate file according to its measurement of congestion at the time. That isn't
what is done with live video, as it isn't feasible to trans-code a stream after it has
been transmitted due to the inherent delays and perception of lag that would introduce.

Given the asymmetric nature of our broadband networks (and NBN incredibly wanting to
make its products *more* asymmetric rather than less), its generally the upstream
direction where congestion is apparent - and the user on the end of one of those links
can turn off their own video to free up capacity for the audio quality to improve. I
generally see this when a user is trying to use a cellular mobile connection - but
even then, in many cases the quality is good. Rarely is there a constraint in the
downstream direction, which is where making a blanket change for all VC endpoints
might improve.


> There were only a few brief dropouts in the audio (fewer than on ABC Radio National
> that morning). This was with Zoom, which is not my favorite product, as there is no
> way for participants to set the audio or video quality to reduce bandwidth. But it
> is possible to reduce data use to around 220 to 300 kbps by making the video window
> smaller.

I find Zoom works very well, and supports better quality and more users for a given
level of bandwidth than most, but horses-for-courses. 220, 300, or even 500 kbps on
the network downstream, or even upstream, is not much these days, and not worth
optimising further. Several Mbps perhaps, 500 kbps no. If links cannot support 500
kbps in either direction, then videoconferencing is not appropriate, and the user
should dial-in instead. (controversial point for discussion ahead) concerns about a
few hundred kilobits being meaningful represents 1990s thinking, not current network
capabiities. If the access networks this decade cannot support, then the networks need
to be improved, not pandering to last century expectations retained. It works fine on
access links with only a couple of Mbps in each direction, which is not an
unreasonable expectation for the 2020s.

> It would be good if the video products, such as Zoom, used a low bandwidth mode with
> a small video window, by default.

With live video such as videoconferencing, bandwidth reduction is done by reducing
frame-rate rather than resolution or window size. Zoom does have controls to reduce
bandwidth (high-def can be turned off), and to reduce frame-rate, at least for
desktop-sharing presentations - again, to control for restricted upstream capacity of
the person doing the presenting.

In my experience, I often find the biggest constraint is not the network, but the
limited processing power of older devices, with sluggish videoconference performance
due to CPU is maxed out decoding and displaying the video without adequate GPU
assistance. We may get better improvements by upgrading people's equipment, instead of
their network connection.

>
> More at: https://blog.tomw.net.au/2020/03/video-conference-on-covid-19-and.html
>
>
Paul.