[Klug-general] HDMI over wifi ... ?

Chris Roberts chris at naxxfish.eu
Mon Jan 19 16:32:19 UTC 2015


I'm a broadcast engineer as my day job, so I've got a bit of experience in
this area.  There are devices specifically designed to solve exactly this
kind of problem.  For example:


They're intended mainly to get preview outputs from digital cinema cameras
to a director without having loads of coax all over your set - but they'd
work perfectly fine for your situation too.  They've got very very low
latency (according to the bumph less than 1ms) so you wouldn't get sync
issues with the audio coming out of the PA.

£579.00 for the pair (ex VAT) is pretty reasonable.

It's a pretty much plug and go solution.  These sorts of devices tend to
use FPGAs or ASICs in order to encode and decode the video quick enough as
well as simultaneously transmitting it.  Whilst it is possible to do the
encoding/decoding on a general purpose solution, you'll have trouble
getting the latency anywhere near good enough for an application like
this.  It might be OK if you're feeding audio and video to an overspill
room (I've previously used Wirecast to do that), but if you're playing
video the sync will be really variable.

Also there are devices which do this over IP - these for example:
They use HD-SDI , since they're designed for professional video (from
cameras and vision mixers) but you can buy HD-SDI to/from HDMI converters
for about £150 each. You can decode on a PC, too - I've done some events
that use that method to get the video into the production switcher.  They
tend to have a SBC with a FPGA/ASIC to do the encoding/decoding in order to
get the video through fast enough.  It is, of course, possible to do this
with two PCs with a capture card and a HDMI output graphics card - but you
have to set things up so it works right on boot, configure networking,
codecs etc. etc. But you will struggle to get the latency you get with a
dedicated solution.

Personally I'd just go for the Paralinx or similar, as you'd get the
flexibility of being able to send anything you like over it and not just a
screen.  You don't have to worry about network configuration, the remote
end loosing it's settings, mounting it safely (they're really small!),
configuring to run everything correctly on boot.  It's no different to
having a really long HDMI cable.  Way less hassle.  If you take into
account the cost of the time taken building a more custom solution, it's
probably even the cheaper option!

Hope that helps!

(sorry it's not very Linux related ;-) )

On 19 January 2015 at 06:28, Thomas Edward Groves <teg451013 at freeuk.com>

> Er socking great stained glass windows?
> Contrast problems, alignment problems.
> And that's just the first three I thought of.
> Apologies for wet blanket.
> Tom
> ----- Original Message -----
> From: Kevin Groves <kgroves at ksoft-creative-projects.co.uk>
> To: Kent Linux User Group - General Topics <kent at mailman.lug.org.uk>
> Sent: Sunday, January 18, 2015 6:25 PM
> Subject: Re: [Klug-general] HDMI over wifi ... ?
> > Projector?
> >
> > Kev
> >
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Chris Roberts
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