Re: Video Capture and Streaming Battle Plan (was:Fluendo, DV capture & other bits and pieces)
On 6/7/05, Herman Robak <herman@skolelinux.no> wrote:
> On Tue, 2005-06-07 at 20:27 +1200, Martin Langhoff wrote:
>
> > The DV capture strategy
> > -----------------------
> > We will capture to HD. We will consume 78GB each day, assuming 5hs of
> > presentations @ 13G p/h. We will have a storage server with more than
> > 1.6TB of space and Gigabit Ethernet between the storage server and the
> > encboxen. Even with Gb ethernet, we don't have enough bandwidth for 3
> > full DV streams -- and it'd be really brittle, LAN file storage isn't
> > meant for realtime stuff.
>
> Isn't your bandwidth requirement off by an order of magnitude?
> Raw DV is 25 mbit/s, so a 100 mb/s LAN could handle three simultaneous
> streams, at least in theory.
You're right -- I just went through the numbers again, I was thinking
4MByte/s which is roughtly what I am expecting and it _does_ fit in
Gb. Still I wouldn't capture to LAN -- the protocols aren't designed
for realtime.
On the other hand all my paranoia about data transfers taking too long
or getting in the way of realtime streams is way off.
> 78 GB per day sounds right. That means only one stream per
> presentation, though. What about the screen? Do you know of
> a convenient way of switching between two cameras, live?
The second camera hits diminishing returns for our efforts.
First, it is harder:
- need to get 2nd camera & tripod
- 2nd encbox or multiple FW ports (unsure about performance encoding
and saving to HD 2 streams on one box)
- finalized videos out of sync
- video compression codecs mess up text, diagrams, etc
And second, it doesn't exhibit much benefit. The projection screen
will have the slides, which will be available from the "talks"
webpage. If we must ask the speaker to say "next slide" or something
like that, users will just follow along. An HTML/PDF/OOffice
presentation file it is so much more efficient, simpler and generally
better the stream.
The only scenario where a 2nd camera could be interesting is if
someone opens a program and does something. However, last Debconf
almost no-one demoed anything on the screen, and those that did,
opened an xterm.
There is no way a compressed video stream if the whole projection
screen is going to show readable text. Because it is compressed,
relatively low-rez.
And hey, we do have a camera operator. If the speaker opens an xterm
and starts doing stuff, frame on the xterm and zoom in until it's
readable (if it ever is!).
So... if we have the time, and the extra cameras and tripods, hell
yeah. But it's a matter of using the gear and time we got to capture
the stuff that is unique -- and that's the speaker's performance.
cheers,
martin
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