[LEAPSECS] TV frame-rate in 60Hz countries

Brooks Harris brooks at edlmax.com
Sun Jan 19 02:31:08 EST 2014


On 2014-01-18 01:14 PM, Peter Vince wrote:

> Stephen Scott has just mentioned his involvement in the TV industry in

> the USA, with its problematical 29.97 Hz frame-rate.


Lets not propogate the notion of a "29.97 Hz" rate, especially in the
the context of this LEAP_SECS list. "29.97" is a commonly used NAME,
shorthand for the correct NTSC rate - 30000/1001 Hz. This inaccurate
representation has been the source of much confusion and bad
implementations over the years.


> I also work in the TV industry, but in the UK where we are lucky to

> have a nice integer 25 Hz rate.

But that 25 doesn't divide evenly very well :-)


> Although historically we still had a problem with leap seconds, as

> the 625 PAL system had a 4-frame ("8-field") sequence (due to the

> exact colour subcarrier frequency being offset from a multiple of line

> frequency to avoid static patterning on monochrome displays), and so

> there were three and one-eighth of these 4-frame sequences per second.

> When editing, this frame-sequence had to be maintained, else there

> would be a small sideways jump when the replay machine kept the signal

> synchronous with the colour subcarrier phase.

>

> Anyway... those problems have largely gone away now that we have

> stopped broadcasting the analogue PAL signal.


The "we" you're referring to is Europe, I think, but other parts of the
world are still broadcasting analogue. Standards rarely escape their own
legacy.



> I was wondering if Stephen, or anyone else, has any information about

> the possibility of 60 Hz countries changing the nasty NTSC-based 29.97

> Hz frame rate to a nice integer 30 Hz rate, as I believe analogue has

> also all but been switched off in the USA too (no knowledge of other

> 60 Hz countries.)


Say "good morning" to the four emperors - UTC, film (24hz), PAL, and NTSC.

-Brooks


>

> Regards,

>

> Peter Vince

>

>

>

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