[opendtv] Re: Half Truths - Was More 1080p@60
- From: Cliff Benham <flyback1@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 07 Dec 2007 18:55:40 -0500
Manfredi, Albert E wrote:
Cliff Benham wrote:
Bert, it's not *video frames* being dropped at all, it's time
code frames that are being dropped so timecode more or less
keeps sync with the video on the tape or the film..
John Shutt described this in great detail. I may still be missing the
bigger problem here, so tell me this:
Let's say that the time codes for the video or film frames could be made
to fit exactly in 30 minute and 60 minute time slots.
If the source video is @60, set the time code generator to non-drop
frame. If the video is @59.94 set the time code generator to drop frame
stream of ATSC video and audio has to be decoded and converted into
standard NTSC for legacy receivers. Would we not encounter the same
problems with the color burst signal beating against the audio carrier,
which originally motivated this whole mess?
No, I don't think so. I have *never* seen this occur in watching the
NTSC video output of about ten different OTA, cable and satellite HD
boxes through 6 mHz analog vestigial sideband [cable TV] modulators over
the last 10 years or more.
I guess, unless the ATSC to NTSC conversion were much more elaborate,
incorporating an odd frame rate conversion function?
Being analog, NTSC TV has some 'slop' in the physical embodiment of the
technical specifications it aspires to.
How else would it be possible to play VHS tapes on a $30 VCR from Woolco
that uses 'rubber bands' to spin the head drum and the capstan and still
get a pretty good color picture from it?
I'm just trying to determine what the issues are, to answer the question
why ATSC had to retain those rates. One might think that as soon as OTA
and cable NTSC go away, the odd rates could also be dropped (because no
broadcaster would be converting any analog source material into
digital). But I think that in fact, they can't be dropped until everyone
stops using the NTSC RF as a convenient interface between DBS, cable, or
OTA STBs and legacy receivers, right?
Bert
Time code has nothing to do with the video signal being broadcast. It
does not leave the broadcast plant with the transmitted signal except by
mistake.
Timecode is used only for editing video in a production suite or for
timing segments of video being played back in an automated system.
Hope I've understood what you are asking....
Cliff
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