[Spice-devel] Streaming video performance concepts

[John A. Sullivan III]

Hello, all.  This isn't a critical question so please do not take lots
of time to answer it unless it would be a helpful general discussion.
We are still trying to properly set our expectations about video
streaming using SPICE on low bandwidth networks.  Indeed, this is our
principle interest in SPICE for Linux as NX still seems considerably
faster for general screen updates.  In Windows, SPICE does seem to be a
bit faster than RDP although the way in which it responds is noticeably
different.  The common advantage on both platforms is the possibility of
video.

Let's take the case of streaming video; by this I mean something like
watching YouTube videos as opposed to playing a locally stored video
file.  If I play this streaming video on my physical desktop browser, I
assume it is using some sort of lossy codec and is probably doing a good
job of saturating say my 2Mbps DSL or cable connection and performance
is adequate.

I am assuming from reading the SPICE documentation (still reading!) that
the beauty of SPICE is that it will detect a rapidly changing screen
area, assume it is video and transmit it using a lossy codec.  So, I
assume, when I open that YouTube video in my browser on my SPICE
desktop, I assume, will also do a pretty good job of saturating my 2Mbps
connection (I confess I've not yet done a packet trace to actually
measure it) with a lossy codec and would expect similar results.

Since both videos are saturating the 2Mbps pipe and both are using
similar(?) lossy codecs, why is the performance so much worse via SPICE
than streaming it locally? Is it strictly a lack of buffering? Is there
something else we can tweak? Or have we fundamentally misunderstood the
protocol and have highly unrealistic expectations? Thanks - John