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HDTV is 20mbps, JVC is 28mbps, humm  

post #1 of 10
Thread Starter 
Gee, the JVC machine seems to get more than the required
data rate for 1080i on the tape, 28mbps vs. the 20mbps
used for broadcast TV.

I wonder, what might that extra bandwidth be used for ?

1080P !!!!!

Yea
post #2 of 10
Quote:
Originally posted by samiam95124
Gee, the JVC machine seems to get more than the required
data rate for 1080i on the tape, 28mbps vs. the 20mbps
used for broadcast TV.

I wonder, what might that extra bandwidth be used for ?

1080P !!!!!

Yea
No, it doesn't relate that way and the max ATSC HDTV payload is 17.1mbs. The rest is for other data. The actual required data rate for 1080i is 1.485gbs. 1080p would be 3gbs. Anything less is compression and a compromise as we well know.

The reason for this additional data rate is that they can do it so why not. It is still downward compatable to MPEG2 decoders. The net result will be less compression artifacts. This is hoped to help the marketing of DVHS over lets say an HD PVR.
post #3 of 10
Thread Starter 
Quote:
Originally posted by Glimmie


No, it doesn't relate that way and the max ATSC HDTV payload is 17.1mbs. The rest is for other data. The actual required data rate for 1080i is 1.485gbs. 1080p would be 3gbs. Anything less is compression and a compromise as we well know.

The reason for this additional data rate is that they can do it so why not. It is still downward compatable to MPEG2 decoders. The net result will be less compression artifacts. This is hoped to help the marketing of DVHS over lets say an HD PVR.
I wish I could say I followed that, but you lost me. How did we
get to gigibits ?
post #4 of 10
I think he means without compression.

Mark
post #5 of 10
I think that 28 Mbps is their DV-to-MPEG-2 conversion rate, so they had to have the capability anyway. Why not allow it's use for prerecorded HD MPEG-2 authoring?

-- Mike Scott
post #6 of 10
Quote:
Originally posted by samiam95124
I wonder, what might that extra bandwidth be used for?
The extra bandwidth would allow the MPEG-2 encoder to apply less compression which results in fewer artifacts. It might even be enough bandwidth to compress 1080/60p without too many artifacts.
post #7 of 10
Or maybe it would allow a slower less expensive encoder to keep up in real time. It takes a lot more work to squeeze the last nickel out of anything.

BTW, when folks here talk about 1080p are they really referring usually to 1080p @ 60 or 1080p @ 24? Because 1080 p @ 24 (movies) doesn't take any more bandwidth than 1080i @ 24 frames / sec and probably a bit less.

- Tom
post #8 of 10
Some of the extra bandwidth is used for 'MPEG trick play', which allows the VCR to grab frames easily while fast forwarding or rewinding.

-D
post #9 of 10
Thread Starter 
Quote:
Originally posted by trbarry
Or maybe it would allow a slower less expensive encoder to keep up in real time. It takes a lot more work to squeeze the last nickel out of anything.

BTW, when folks here talk about 1080p are they really referring usually to 1080p @ 60 or 1080p @ 24? Because 1080 p @ 24 (movies) doesn't take any more bandwidth than 1080i @ 24 frames / sec and probably a bit less.

- Tom
Yes, I think it means 60hz. I agree the requirements are odd.
60hz is what you need to get rid of flicker in the direct scanning
set, but most expensive sets don't direct scan, but convert
to high scan rates via a buffer internally. Since most interesting
sources are film at 24hz, its hard to see what is accomplished,
but then I don't see anyone doing the 1080p @ 24 format that
these real world facts would seem to make obvious.
post #10 of 10
Quote:
Originally posted by trbarry
BTW, when folks here talk about 1080p are they really referring usually to 1080p @ 60 or 1080p @ 24?
I think that 1080p usually refers to 1080/60p, but it could also refer to 1080/30p or 1080/24p. Similarly, 720p usually refers to 720/60p, but it could also refer to 720/30p or 720/24p.

1080i obviously refers to 1080/60i. ;)

It can be even more confusing if the material originated at 60p, 60i, 30p, or 24p and temporal conversion was performed.
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