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JVC GY-HD Series Camera Systems
GY-HD 100 & 200 series ProHD HDV camcorders & decks.

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Old August 24th, 2005, 01:00 PM   #1
HDV Cinema
Join Date: Feb 2003
Location: Las Vegas
Posts: 4,007
720p60 and HD100+

Some facts:

1) ASTSC 720p60 uses 15-frame GOPs (as does 1080i and Sony HDV)

2) JVC 720p30 uses 6-frame GOPs:

3) JVC PROS: Requires less memory in encoder/decoder; more frequent I-frames (5 per second) so should handle motion much more precisely.

4) JVC CONS: More I-frames means more data coming-out of encoder and so a higher data rate needed for recording.

5) 720p30 inputs to the encoder half the pixels/second as 720p60 -- thus the 19.4Mbps (used for 720p60 and HDV) provides a huge headroom(2X) for the greater data output of a 6-frame GOP encoder.

6) If JVC supports 720p60 using 6-frame GOPs they will need 2X more recording band width.

7) BUT if JVC uses SHORT GOPs with 720p60 -- then they would not.

8) Why the difference? Beceuse "6-frame" is absolute while "short" is relative.

9) Short with 30fps is 6 -- that's 5 I frames per second.

10) Using the same definition of "short" the GOP length for 720p60 is 12-frames: 5 I frames/second and 5 GOPs/second.

11) If JVC chooses a 12-frame GOP at 19.4Mbps they would offer MOTION handling as good as 720p30, but slightly less QUALITY than 720p60 ATSC.

12) If JVC chooses a 15-frame GOP at 19.4Mbps they would offer QUALITY equal to ATSC 720p60, but the MOTION handling would not be quite as good as 720p30.

13) Chosing a 12-frame GOP has the advantage of being simply 2X 6 frames. Choosing, 15-frames makes 720p60 HDV exactly the same as ATSC 720p60.

14) Either choice means the playback system of ANY JVC HDV product can generate an i.LINK stream. Obviously, the decoders in the HD1/HD10 can't decode 720p60. And, likely neither can the one in the HD100. (Unless 60Hz is only a firmware upgrade.)

15) By inserting a new encoder/decoder into the HD100--everything is set for a 720p60 camcorder. When would JVC do this? If I had the new encoder almost done -- I would introduce the HD200 the day Panasonic announces a shipping date for their P2 camcorder. And, I'd price it at $500 lower than the P2 with media. Probably, about $9,900. This wouldn't screw the HD100 buyers -- too much. Also by then, a better lens could be included.


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