[linux-dvb] Re: [OT] Reality

[Gavin Hamill <gdh@acentral.co.uk>]

On Saturday 15 May 2004 05:24, Jerico Webmail wrote:

>I am seeing
> more newsgathering people using MPEG-4 and interestingly we will be testing
> MPEG-4 multicasted over IP encapsulated in DVB very soon. If demand for
> HDTV grows the money people may demand MPEG-4 to save bandwidth but more
> likely just higher modulation schemes (8PSK).

Apart from the sitting-in-a-dark-room-for-half-a-day part, your job sounds 
interesting :) All the technical aspect of television without having to worry 
about the quality of the programming =)

> I'm also interested to see how many broadcasters make the transition to
> 8PSK over satellite for DTH. 

I didn't even think there were any other options than QPSK - I stand 
corrected :)

> I must say, we've tried using 16QAM over 
> satellite (for DVB-IP) and even with a 2.4m antenna and stressing the
> satellite transponder the reliability is quite poor. I wouldn't hope for
> 16QAM anytime soon over satellite, 

Yep, and some cablecos are really packing it in at 128QAM... I just love the 
phrase 'constellation density' - it sounds like it was designed by geeks, for 
geeks to the exclusion of all else =)

> but 8PSK is more than ready for 
> deployment when the receivers can be deployed. Alot of outside broadcast
> sporting events are using 8PSK and where a decent setup can be deployed and
> demand is high the occasional 16QAM is used.

Out of curiousity, what kind of additional bandwidth is 8PSK giving?

> For a channel 15Mbps is very nice bandwidth, but if thats being sat muxed

I'm quite sure the '15Mbps' is purely for show, since the AV7110 is unable to 
decode streams of more than 10Mbps, and this chip is used in various STBs not 
to mention our old friends, the 'full feature' PCI cards from Siemens/Fujitsu 
et al.

(if I'm wrong here, please correct me)

> then that could take a big hit. The biggest problem with DVB broadcasting
> is that no one will pay for pre-processing of the media, 

<nod> I was involved with a VHS -> XviD project for a while, and the amount of 
VirtualDub filters we had to send the raw analogue capture through just to 
get a decent quality encode was quite mad. Even on a highly specced P4, 
processing 480x360 (I think..) data was running at one or two frames per 
second max.

The output *was* worth it though - MPEG4 with very little background noise / 
artefects / movement, so all the bitrate was truly going to describing the 
action.

> Snell & Wilcox provide some lovely processing hardware that claim to be
> able to save significant bandwidth by preprocessing analogue noise out.

I bet there's some insane FPGA and other custom DSP stuff going on in there, 
and a price tag to boot to be able to do that in realtime and at broadcast 
quality..

Cheers,
Gavin.
--
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