[opendtv] Re: Frames Per Second of 720P

  • From: "John Shutt" <shuttj@xxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Fri, 18 Jul 2008 14:44:25 -0400

Russ,

Further investigation revealed the 80 bit SMPTE timecode word and the allocation for each bit. There are indeed 32 bits allocated to 8 user fields (four bits per field,) 2 bits allocated to both the tens frame and tens hour fields, and 3 bits allocated to both the tens second and tens minute fields.

I don't seem to find where a even or odd field is flagged, however, unless the bit 11 Color Frame bit is used for this purpose. How is a 'field' flagged in 720p60 SMPTE timecode for purposes of frame accurate editing?

John

----- Original Message ----- From: "Russ Wood" <russ.wood@xxxxxxxxxxxx>
To: <opendtv@xxxxxxxxxxxxx>
Sent: Friday, July 18, 2008 11:23 AM
Subject: [opendtv] Re: Frames Per Second of 720P


John, SMPTE 12M only has two bits to define the tens of frames in the
timecode.

SMPTE 12M-1 section 12 says that the time address should increment only
every other frame, the field mark should be used to differentiate
between the two frames labelled thus.

SMPTE 12M-2 section 9.2 says that Progressive TV systems with frame
rates greater than 30 frames per sec a single time address should
identify a pair of frames.

Is the kit you are using double counting the frame addresses and adding
one for the second.

Russ Wood


-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]
On Behalf Of John Shutt
Sent: 18 July 2008 13:37
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Frames Per Second of 720P

The Sony brochure
http://bssc.sel.sony.com/Professional/docs/brochures/mvs8000.pdf states
that
the switcher operates at 1080i60, 1080i59.94, and 1080i50.  This is
probably
where the Sony rep got confused, because 1080i60 is indeed 30 unique
frames
per second, and 1080i59.94 averages out to 29.97 unique frames per
second.

This is exactly why I don't understand the nomenclature that seemed to
only
come into fashion with the advent of HD, of calling 1920x1080 thirty
frames
per second interlaced as "i60"  Read the timecode, there are 30 frames
per
second in the timecode, therefore it is a thirty frames per second
(ignoring
the 1.001 for the moment) format, and should be called "i30" which
clearly
states 30 fps, presented interlaced.

When recording "1080i59.94", you can frame advance through the timecode
and
watch the time change from 00:00:03:29 to 00:00:04:00.  In contrast,
with
720p59.94, you can watch the timecode change from 00:00:03:59 to
00:00:04:00.

"1080i60" looks better on paper next to "720p60" I suppose.

John

----- Original Message ----- From: <dan.grimes@xxxxxxxx>


I just attended a demonstration of a Sony MVS8000 production switcher.
The
switcher can output 720 at 59.94 P and 1080 at 29.97 I.

As I we discussed frame stores, I asked if it took 60 frames to store
a
one second motion clip (120 with a key) and they said no, only 30.
They
(multiple Sony reps) were telling me all video is 30 frames per
second, no
matter what the format.





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