[opendtv] Re: IP-Based TV Will Revolutionize Entertainment
- From: Kon Wilms <kon@xxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sun, 01 May 2005 16:01:07 -0700
On Sun, 2005-05-01 at 18:23 -0400, Manfredi, Albert E wrote:
> IP is a routing protocol, layer 3, described in RFC 791. It
> doesn't begin to specify what an IPTV (or any other DTV)
> needs to interoperate with client hosts. Kon may be correct
> that all IPTV schemes use XML for layers 5-7, I have no way
> of knowing. I've never seen a comprehensive survey of IPTV
> systems deployed so far. (But I would be amazed if they were
> interoperable.)
Well, I didn't say that. I said that people have been using XML-based
meta-tagging for a long time already.
> Even the new media darling, Bit Torrent, doesn't get away
> with any of this. BT is essentially a layer 5 scheme, session
> layer. It works on top of TCP, and it orchestrates a
> choreography of TCP downloads from a number of different
> servers. The question remains, after the download is
> reconsituted into the appropriate file, what have you
> downloaded and how is it read? Is it a big MS Word file? Is
> it Acrobat? Is with WM10? Heck, is it ATSC over MPEG-2 TS
> (why not?).
That's not rocket science either. I don't claim to be the first but
here's something to illustrate which I did for my own media center
project 6 years ago: http://sourceforge.net/projects/idvx/
The *only* tough part is how to tie the delivery and synchronization of
the meta-data files with the actual content. I just stuck them on the
back of files as a binary blob, problem solved. Parse the header for
MIME information, parse the EOF+blob block for meta-data. All that is
required is the file.
> The ATSC and the DVB have devised a very efficient way to
> fully define DTT streams. Furthermore, with A/90 and the
> DVB equivalent (whatever that is), they have opened the
> doors to almost limitless options for upgrading the
> standard, subject only to the one-way broadcast environment
> DTT operates in. In principle, even XML and some one-way
Who today is using the A/9x data-broadcast standard? No-one? It is using
SDP for meta-data, which itself is severely lacking in the description
component, and is for all intent purposed useless for rich meta-data
description. It offers no capability to cross-reference media, or
provide multiple level s of descriptive data for the target's UI and
machine parsing categorization components. Of course, you can extend it
with your own a=attribute:value parameters but that completely
eliminates any interoperability with other products.
Maybe we could use it to transmit XML files containing the real
meta-data! And I know that's what some folks believe is the correct
approach. So then I ask: why the duplication of effort into the SDP
payload ala description tags. Conclusion - this obviously isn't the
case, and this framework is woefully inadequate for any real use.
Anyone with a data-casting system has implemented things far advanced
over SDP, partly because it was late to the party (actually it should
have been left to die on the MBone VIC/RAT floor IMHO), and partly
because it isn't really that useful for delivering anything except
streaming media.
Thats just my 2c though.
> version of Bit Torrent could be transmitted
I've seen a name for that - swarm-casting. Has anyone really implemented
it? I don't think so. There was talk in the iBlast project about
utilizing this model for delivery, both to increase speed and for
reliability purposes. In effect you can do this if you have the right
carousel system and a virtual ethernet board that doesn't drop the IP
address on retune.
Cheers
Kon
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