[Tig] drop frame and HD

James DeLuca james_deluca
Wed Mar 16 22:04:32 GMT 2005


>Jack James wrote:
>With NTSC SD video, you have drop-frame (DFTC) and non-drop (NDFTC) timecode.
>I understand ... that the [NO] actual frames [are dropped, but] that DF drops two frame [counts] a minute, [for] 9 out of every 10 minutes.

>But with HD ... you have 59.94i and 60i formats. 
How does this work in terms of timecode? 
Is 59.94i drop frame and 60i non-drop? Or are the two completely independent, requiring standards conversion to go from one to the other? 
Because let's face it, it doesn't seem to make sense to talk about a 59.94 (or 29.97) non-drop timecode does it? 
And. where exactly does 23.98 fit into all of this?
...explain this ... in terms of the number of actual frames of each...

Jim:
Drop-Frame timecode was created for broadcasters to better co-ordinate tape-time with clock-time (1 hour of Full-Frame timecode tape runs 3 sec, 18 fr too long (108 fr/hr)).
Hence, it is ONLY used with non-integer frame rates; of which only 23.976, 29.97, and 59.94 are common-place. The odd-man out is that 23.976 (aka 23.98) timecode is only offered in Full-Frame format (AFAIK).

FYI: The D-5 HD machines have NO format differences on tape between recordings made from 1080p/23.98, 1080p/23.98sF, 1080p/24sF, and 1080p/24 signal inputs. On tape, all are segmented with the I/O converting between progressive and interlaced (aka segmented) modes. Ordinarily, all digital audio I/O is sample rate converted with only the 1080p/23.98 and 1080p/23.98sF modes permitting a turn off of those convertors for use with Dolby Digital (aka AC3) and Dolby-E.
Right now, any D-5HD ~24fr tape has integer output timecode when locked to 24hz ref, and 23.98 HZ timecode when locked to NTSC video ref.

After the analog transmitters shut down, I was hoping their would be a quick switch to true 60Hz video in the US. I forgot that with set-top boxes downconverting to encoded composite NTSC, we cannot switch frame rates without causing havoc to those NTSC receivers, whose internal sync circuits might not lock reliably if at all, lock to h & v but not subcarrier, etc. (That's a lot of tv's, vcr's, TiVo's, & DVD-R's.)
Then again, all the units with SD component I/O (RGB or YPbPr) should be okay as long as they can lock vertically. Hey, I might even see 60Hz video in my lifetime.

When true 24Hz (or 60HZ) outputs are the norm, how are we going to get the Dolby audio off tape?

James DeLuca, Sr Video Engr. 
Crest National Digital Media Complex - Hollywood





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