FYI: Comcast digital TV in Cambridge

[Jarod Wilson]

On Thu, 2008-12-04 at 15:56 -0500, Mark J. Dulcey wrote:
> Jarod Wilson wrote:
> > 
> > Are we talking h.264 here or mpeg2? I can tell you from first-hand
> > experience, you can NOT stream 1080i mpeg2 hdtv content over 802.11g
> > with any sort of reliability. Too much packet loss, and while g claims
> > 54Mbps throughput, I've never seen better than a sustained 2.4MB/s
> > transfer, which is about what most 1080i mpeg2 streams require.
> 
> I was thinking of ATSC content which is 18Mbps maximum, or about 
> 2.25MB/s; a clean 801.11g connection can just about manage that, though 
> you had better not have much else happening on the network.

I probably had another device or two (or three) on the wireless network
at the same time, but I really have tried streaming 1080i stuff over g,
and its absolutely miserable -- prebuffering pauses every few seconds.
Part of it may be that mythtv isn't as forgiving of packet loss and
latency compared with mplayer. A quick look at some 1080i recordings on
my backend shows them weighing in between roughly 16 and 18 Mbps.

> HD from 
> cable uses substantially lower bit rates, making the problem easier; I 
> don't know of any cable company that sends HD at more than 10Mbps, and 
> the systems that are using H.264 are probably using even less. (FIOS may 
> be an exception; they've got bandwidth to burn.)

Yeah, FIOS here.

> There is a tradeoff 
> between quality and channel capacity, and the cable guys always choose 
> the latter because it's a stronger marketing point. People using cable 
> for HD... trying hooking up an antenna and watching some broadcast ATSC, 
> especially from WGBH, and see how much better it looks than the same 
> stations on cable.

Indistinguishable for me, but again, FIOS.

> Blu-Ray 1080p content may need higher bit rates, and therefore 802.11n.

Yeah, I'd wager slightly higher bit rates. From what I understand, h.264
achieves roughly the same quality as mpeg2 at about 60% the file size
for the same resolution, so say (.6 * 18Mbps * 2) for 1080p would be
21.6Mbps, assuming the content isn't letterboxed for original film
aspect.

--jarod