[mythtv] Idea for interlaced playback.
Stephen Williams
stephen.gw at gmail.com
Mon Nov 14 09:49:42 EST 2005
On 15 Nov 2005 00:35:00 +1030, Ian Dall <ian at beware.dropbear.id.au> wrote:
> Bjørn Konestabo <bjornko at math.uio.no> writes:
> I get good results with the following mode.
>
> # Sync Timing PAL: Horizontal frequency 15625 Hz. H sync width 4 uS (58 dots). Vertical frequency: 25 Hz, Vertical Sync width: 192 uS (6 lines).
> Mode "720x576"
> DotClock 14.5
> HTimings 720 752 816 928
> VTimings 576 580 586 625
> Flags "Interlace" "-HSync" "-VSync"
> EndMode
>
>
> I don't recall exactly, but I found a real spec of a PAL signal to
> work out the timings. While the vertical resolution is defined by the
> number of scanlines, there is no counterpart for horizontal resolution
> in analog tv, so the dotclock could change if the horizontal
> resolution changed. The vertical sync width you have to work out as if it
> is non-interlaced 50 hz.
I got the following numbers directly from the PAL signal specification:
Horizontal Frequency = 15.625kHz
Vertical Frequency = 50Hz
Horizontal lines (total) = 625
Horizontal lines (visible) = 576
Horizontal Front Porch = 1.5µs
Horizontal Sync Width = 4.7µs
Horizontal Back Porch = 5.8µs
Horizontal blanking period = 12µs
Vertical Front Porch = 0.16ms
Vertical Sync Width = 0.16ms
Vertical Back Porch = 1.28ms
Vertical blanking period = 1.6ms
Nvidia restrict some of the values in their modelines to multiples of
8. Taking that into account this is the closest possible modeline for
720x576 to the PAL spec for an nvidia based card:
ModeLine "720x576pali" 13.875 720 744 808 888 576 581 586 625 -hsync
-vsync interlace
Hope that helps.
Steve
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