[MEncoder-users] Flashvideo for YouTube using mencoder

[Ben]

On Fri, Feb 22, 2008 at 9:28 PM, RC <cooleyr at gmail.com> wrote:

>  B&W NTSC was exactly 30fps.  With color, the frame rate was slowed
>  slightly so that the luma and chroma would be offset, to prevent
>  interference between the two.

That last part is a myth. Given the nonlinear distortions of the television
transmitters and receivers of the time (1953) it was feared that the *sound*
carrier (4.5MHz offset from the vision carrier) might generate interference
products with the chrominance subcarrier (3.579 MHz) resulting in a
spurious 920kHz interference that would be quite visible.
The NTSC color subcarrier has a value related to half the horizontal
scanning frequency (Fsc = 455/2 Fh) and to the vertical scanning frequency
and thus achieves low visibility due to a process of line-to-line
phase reversal.
By making the 4.5MHz intercarrier spacing a multiple of Fh/2, the 920kHz
interference visibility would also benefit from the line-by-line phase reversal.
Since the FCC opposed the change of the carrier spacing (it's all their fault!)
the only way out was to change the horizontal and vertical scanning
frequencies. So we ended up with Fv = 59.94Hz instead of the original
60 Hz and with Fh = 15,734.25Hz instead of the original 15,750Hz.
We still live with the consequences of this decision.

JB