Key with HDV

[Gary_McClurg]

Thought I'd pass it on.

Interesting, about HDV and keying.

Look for

Somebody tries to key HDV footage-sample images and footage available*

http://www.hdforindies.com/

 

[Isaac_Brody]

Keying that stuff looks like a nightmare. HDV compression plus interlacing looks like a beatch.

Here's a direct link to the HDV project from hdforindies.

http://www.filmages.com/HDV_test/


Any HDV people here managed to get a good key from FX and Z1 footage?

 

[Isaac_Brody]

Oh and you can download a 13 reference frame avi off that site to try and key if you want. I'm going to play around with it and see if I can get a decent key. Doubtful though.

EDIT: You need Final Cut or Imovie to use that avi.

 

[Flintstone]

I wonder how keying 720p will look like with HDV at 19Mpbs? Time will tell.

 

[Barry_Green]

Depends on the overall frame rate -- if you're talking about 60p, it'll be problematic, but for 30p or 24p it should be better than the 1080i version. You have a lot more bits per pixel in 720/24p or 720/30p (although the shorter GOP may render that advantage null, remains to be seen), but at the bare minimum you'd eliminate all interlace artifacts.

 

[Flintstone]

This is something I don't understand. Why would a shorter GOP be a disadvantage? My first impression of a shorter GOP would be that it is better, because it has less to estimate between I-frames. So what is it I am not understanding here? :undecided

 

[Barry_Green]

The longer the GOP, the more frames are compressed using the much-more-highly-compressed B and P frames. I-frames take up the most space. The shorter the GOP, the more frequently I-frames show up, which means that in the overall bitstream, more bits are being devoted to I-frames, which means less overall efficiency is possible. B and P frames are extremely highly compressed, and take very few bits, so the longer the GOP goes, the more raw data can be applied to the initial I-frame.

But there are disadvantages as well. Sony obviously recognizes this with MPEG-IMX, they made it I-frame-only, with no GOP at all. This totally eliminates the variable-resolution panning "breakup" that happens. (anyone else watching the NCAA tournament on HD? On static shots it's magnificent, and on panning shots it's horrible! and there's a persistent half-second out-of-focus-to-in-focus issue... all this happens because of the highly compressed bitstream and the long GOP). However, they're cramming a full high-def image into just 19 megabits, which is an amazing accomplishment, and when it looks good, it looks incredibly good.

720p HDV should, theoretically, look pretty good. It has a shorter GOP, but at the frame rates JVC's talking about (24p and 30p) it has less than half the pixels per second to worry about. Of course I think it'd look a lot better if it was 4:2:2, but I'm definitely interested in seeing how the footage stacks up.