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Ignoring the political/copyright aspects of this, I am trying to figure out the pros/cons of these two competing digital video connection standards. I'm hoping experts here can help me understand these things better.


DVI:

* Uncompressed stream

+ Easier to process for a display - no decompression necessary, just display it directly

- Less ideal connection for a recording device - the signal would have to be re-compressed.

- Higher bandwidth = heftier cabling, more expensive to implement on a device, point-to-point connection only

+ Already exists in some formats (LCD computer monitors, is that the same DVI?)

+ Gobs of bandwidth, fewer format-compat problems since its raw data.



Firewire:

* Compressed stream

+ Better for input to a PVR or HD-VCR since its already compressed

- Components attached have to mutually understand the format of the stream

+ Cheaper to build a satellite/cable box - no decompression, just pass through the tuned signal

- More expensive to support in a display - requires that the display includes a decompressor (I assume this is why all the Sony sets that include firewire also include an ATSC tuner - most of the hardware was already required to accept the firewire connection?)

+ Lightweight cabling, bus/chaining connections

- Maybe not enough bandwidth?



It seems in general if I setup a system around Firewire (in the future, when all this stuff actuall exists) I would pay more for my monitor/display, but less for associated boxes like tuners and recorders. With DVI, I could get a cheaper display and would pay more for an external tuner/recorder. The firewire model would seem to match more closely how people treat digital audio today - keep it compressed (Dolby Digital, DTS) in the components and only decompress it when it hits the output device (receiver). I guess the DVI-equivalent in audio would be the external 5/6-channel inputs on receivers to support outboard decompression, which are a bit less popular than the integrated models for most consumers..

 

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Quote:
Originally posted by Innerloop:
DVI:

- Higher bandwidth = heftier cabling, more expensive to implement on a device, point-to-point connection only
It's actually less expensive to implement on a device--Silicon Image's DVI/HDCP interface chips are $15 an end and there is no need for any real computing power in the display past the chip--you just shift the decrypted raster onto the screen. Uncompression/decoding of HD MPEG-2 is a fairly compute-intensive process, and any display with a 1394/DTCP connection has to have that computing capacity and a DTCP encrypting/decrypting Firewire interface chip--more expensive than DVI alone in the display.
Quote:
Firewire:

+ Cheaper to build a satellite/cable box - no decompression, just pass through the tuned signal
Well, that's the choice of the implementor of the box--Sony's cable box with 1394/DTCP connections assumes that there will be an MPEG-2 in the display, probably because Sony is shipping 3 sets with 1394/DTCP connections and built-in ATSC tuners (and therefore HD MPEG-2 decoding). Echostar, on the other hand, is talking about putting both 1394/DTCP and DVI connections on their copy-protected STB, which would require that it contain an MPEG-2 decoder (they would be wise to also put HD analog component video outputs on it too, even if it'd have to constrain the resolution of HD subscription movie channels and HD pay-per-view).
Quote:
- More expensive to support in a display - requires that the display includes a decompressor (I assume this is why all the Sony sets that include firewire also include an ATSC tuner - most of the hardware was already required to accept the firewire connection?)
Yep--the lion's share of what's necessary for an ATSC tuner is necessary for displaying from a 1394/DTCP connection alone (hardware wise--there is quite a bit more software involved in dealing with ATSC).
Quote:
- Maybe not enough bandwidth?
400 Mb/sec is plenty of bandwidth--it should never have to carry more than 3 or so simultaneous HD broadcast streams, which can't exceed (or even equal) the 19.39Mb/sec capacity of its 6MHz channel. There is some overhead added by DTCP headers, and encryption probably increases the size of the data a bit, but not anywhere near enough to make up the difference.

Quote:
It seems in general if I setup a system around Firewire (in the future, when all this stuff actuall exists) I would pay more for my monitor/display, but less for associated boxes like tuners and recorders. With DVI, I could get a cheaper display and would pay more for an external tuner/recorder. The firewire model would seem to match more closely how people treat digital audio today - keep it compressed (Dolby Digital, DTS) in the components and only decompress it when it hits the output device (receiver). I guess the DVI-equivalent in audio would be the external 5/6-channel inputs on receivers to support outboard decompression, which are a bit less popular than the integrated models for most consumers..
I agree. The only way that DVI becomes cheaper is if there is a central, modular decompression device. This could be an STB like Echostar's--it should have two 1394 connectors, to allow for daisy-chaining: if it could somehow allow the television to request video received from elsewhere in its 1394/DTCP network, decrypt it, decompress/decode it and re-encrypt to move it downstream in HDCP (no mean task, in realtime, but probably no more intense than what it has to do to tune and decode what it receives from its satellite dish to be moved to the set over DVI/HDCP), it could serve this purpose. It really doesn't make any sense for your cable or DBS STB, PVR and HD-VCR to all include the capability to decode HD MPEG-2, and it will definitely increase the cost of them. It will also decrease security, providing multiple points at which to try to obtain decrypted video, which is counter to the point of this entire excercise (another point in favor of 1394/DTCP in the set--the video need never be decoded outside the display).


-- Mike Scott


[This message has been edited by michaeltscott (edited 09-20-2001).]
 
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