[Dprglist] odometery test movie

Karim Virani pondersome64 at gmail.com
Mon Jul 13 11:21:17 PDT 2020

Hey David, regarding your questions about sharing video...

Bottom line - we could switch to Google Meet (from Hangout Meets which I
think we are still using) and anyone who wants to share a video should post
it on a video streaming service like youtube ahead of time. You can post it
as "unlisted" if you don't want it showing up in search engines. This will
let us use the Share Chrome Tab feature
with its support for high quality video streaming. It's important to *not*
use the full screen or application share options here.

If you want the details, read on:

We are asking a lot of our systems when we share video while presenting our
desktops. At the very least your system is decoding that video to raw
(possibly up scaled) pixels. So you've lost the inter-frame optimizations.
If the source is remote you are also consuming downstream bandwidth. Now if
you are sharing your desktop, screen updates are being broken down with
VNC-like (I'm not sure what remote rendering engine Meets uses) frames. The
system tries to optimize things down to simple graphics primitives for a
lot of the screen drawing like text and vectors, but bitmaps have to be
re-encoded. Your decoded video is now a series of high res bitmaps updated
at your native screen refresh rate. Even if your video source is skipping
frames, your screen buffer doesn't know that. So now you have an
uncompressed high hz sequence of high res bitmaps that have to be
re-encoded and the VNC subsystem is usually able to detect and treat this
at least as a motion jpeg stream which gives up the interframe differencing
optimizations. Now you have a higher bandwidth, lower quality and less
optimized video embedded within the screen frames you are uploading to the

If you have a fast processor and high bandwidth upstream internet service
you might get away with this. But at best it's still going to be lower
quality with extra layers of compression artifacts than your original
video. Likely it will stutter badly if there are any bottlenecks in the

When you point your webcam at a screen you are already at lower pixel count
because the video resolution of most webcams is capped well below screen
resolutions. It's also using interframe optimizations and some webcams do
this internally and not on the host processor. It's definitely not having
to do a decode first and it's not consuming downstream bandwidth.

It's hard to discover the details of how they did it, so I'm speculating
here. But Google Meet is claiming it supports high quality video and audio
sharing. Since you have to use the Chrome browser for this feature, they
might just be using the Casting function built into the browser - which I
think is smart enough to echo back the source video stream without recoding
it. It's also possible that it is detecting the source video stream and
just telling the broadcaster to share the cloud source with all of the
meeting participants - skipping the need to upstream from your local
computer. So you are only providing start/stop/seekcommands. That at least
is how video streaming works for the larger (thousands of participants)
conference sharing services.

Anyhow, I'd be happy to test it out with you and see if we get an
improvement. We could try this in a one-to-one anytime convenient to you.
Google Meet is free to everyone now. But you have to basically "cave in to
the man" and adopt the whole google pipeline (Meet/Chrome/Youtube). Though
it's possible it will work with the mpegs you post on the SMU server.

Sorry if I went into too much detail. In a previous life I built some of
the first mpeg streaming servers - the early 90s.

On Sun, Jul 12, 2020 at 11:58 PM David Anderson via DPRGlist <
dprglist at lists.dprg.org> wrote:

> Hello DPRG,
> Here's the video I mentioned in the meeting Saturday but forgot to post
> the link:
> http://www.geology.smu.edu/dpa-www/robo/mpeg/rcat-202005-9-2.mpg
> Still haven't figured out how to show video in google meetup. Lou
> mentioned that also.  Maybe it's not possible.  It did seem to work at
> last months meeting when I just pointed the laptop camera at the desktop
> screen, and played the video on the desktop.  But the "presenter"
> function doesn't seem to be able to keep up.
> Likely I just don't know what I'm doing.
> onward into the fog,
> David
> _______________________________________________
> DPRGlist mailing list
> DPRGlist at lists.dprg.org
> http://lists.dprg.org/listinfo.cgi/dprglist-dprg.org
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