[opendtv] Re: Frames Per Second of 720P

  • From: "Russ Wood" <russ.wood@xxxxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 28 Jul 2008 15:09:16 +0100

Sorry it has taken so long to answer these questions, I have been out of
the country for a week.

The field bit is VITC bit 35 (LTC bit 27) for 30frame/60 field, 60 frame
and for 24 frame, it is VITC bit 75 (LTC 58) for 25 frame/50 field and
50 frame.

For 50 and 60 frames/second the coding of the T/C cannot hold the higher
number of frames tens so preference is that the field bit is zero on the
first frame of a pair and 1 on the second frame.

With interlaced video, each field will usually carry the same T/C as its
predecessor or its successor, the first field of a particular T/C value
is normally marked with field bit set to zero, the second with field bit
set to 1 (same as the progressive high frame rate coding).

So there are natural pairs of fields that are bound together into a
frame, notwithstanding the possibility of the boundaries slipping
without any visual disturbance.

Russ Wood

-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx]
On Behalf Of John Shutt
Sent: 18 July 2008 19:44
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Frames Per Second of 720P

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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