[mythtv-users] Custom Modeline
Cory Papenfuss
papenfuss at juneau.me.vt.edu
Sun Jun 20 10:13:52 EDT 2004
I looked at it, but I fail to see how the 'videogen' program is any
more intuitive than calculating the modeline yourself. They are easy to figure
out:
Modeline mymode FF H1 H2 H3 H4 V1 V2 V3 V4 FLAGS
FF: dotclock frequency (MHz)
Hx: horizonal description (number of FF dots to count)
Vx: vertical description (number of horiz. lines to count)
FLAGS: special stuff maybe necessary for drivers (sync-on-green, sync polarity,
interlacing, etc)
Lines are drawn by counting pixels of the dotclock, but also needs to describe
what happens off the edge of the screen.
H1 is picture width in pixels (e.g. 720)
H2-H1 is the black space on the right side of the screen
H3-H2 is the length of the sync pulse to tell the monitor to reset to the
beginning and start drawing another line.
H4-H3 is the black space on the left side of the screen
HHHHHHHHHHH___----___HHHHHHHHHHH___----___HHHHHHHHHHH___----___HHHHH...
0 H1 H2 H3 H4 H1 H2 H3 H4
The vertical is exactly the same, except it uses complete lines to count,
rather than individual dots. Here's the line I use for my custom NTSC hardware
board (720x480 at 59.94Hz interlaced)
Modeline coryntsci 14.318 720 760 824 910 480 484 492 525 interlace
14.318 MHz dotclock
H:
720 picture pixels
760-720 (40/14.318e6)=2.78us black on right side
824-760 (64/14.318e6)=4.47us sync pulse width
910-824 (86/14.318e6)=6.01us black on left side
Total horiz line is 910/14.318e6 = 63.556us => 15.73 kHz (sound familiar?)
V:
480 picture lines
484-480 (4/15.73e3)=254us black on bottom
492-484 (8/15.73e3)=508us vertical sync pulse width
525-492 (33/14.73e3)=2.1ms black on top
Total vert frame is 525/15.73e3 = 33.36ms => 29.97 Hz (sound familiar?)
It might seem complicated, but it's really pretty simple once you
understand what's it's doing. Just a matter of counting dots. The tough part
(sometimes) is finding the spec for the video signal (sync pulse widths, etc).
If you wanted to move the picture to the left a bit without changing anything
else, add 5 to H2 and H3.
Hope that helps some folks
-Cory
*************************************************************************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
*************************************************************************
On Sun, 20 Jun 2004, David wrote:
> Hi
>
> Here's some text I've put together for Modelines
>
> It's up at www.mythtv.info/moin.cgi/ModeLineHowTo
>
> Any comments please feel free to visit and edit.
>
>
> Modelines
>
> OK, so you want to generate a modeline for X for your HDTV / Projector...
>
>
> What's a modeline?
>
> It tells your videocard how to draw a picture on your display
> (monitor/TV/projector etc) Each display has different capabilities. Most
> obviously they have different sizes and resolutions.
>
> Each modeline describes how to achieve a given resolution.
>
>
> And why would I care?
>
> When ever you look at something on your display it's shown at a certain
> resolutions and certain refresh frequencies. Some displays will happily
> accept video signals for different resolutions and convert them for you - the
> problem is that this can reduce the quality of the video signal. So ideally
> you'll get myth or xine to convert your signal once to the right resolution
> for your tv/projector and avoid unnecessary degradation.
>
> Simply - it can look better.
>
>
> My Problem
>
> I have a Panasonic AE100 LCD projector. I want to set it up to get the best
> posible resolution.
>
> The book tells me it has a native pixel size of 858 x484. It also lists the
> video modes it supports with various frequencies.
>
> I pick 856 x 480 with the following frequencies:
>
> *
>
> 30.057 kHz Horiz scanning frequency
>
> *
>
> 60.114 Hz Vert scanning frequency
>
> *
>
> 31.500 MHz Dot clock
>
> So the problem is "How do I create a modeline given this input data?"
>
> A google returns a few options (some listed below) the most promising seemed
> to be videogen.
>
> Being a Debian user a quick apt-get install videogen has me up and running.
>
> man videogen is useful - the most important options being:
>
> -m=XxY describes the mode you want a modeline for
>
> -mdc=xx sets the maximum Dot-clock /of the videocard/, not the
> monitor
>
> -mhf=xx sets the maximum horizontal frequency for your monitor
>
> -mvf=xx sets the maximum vertical frequency for your monitor
>
> -dvf=xx sets the desired vertical frequency for your monitor (I
> use pal so I'd like it to refresh at 50Hz)
>
> It's not obvious how to use it though, the HTPC How To
> <http://www.mythtv.info/moin.cgi/HowTo> suggestion didn't work but after a
> bit this command produces the desited results:
>
> $ videogen -m=856x480 -mdc=34 -mhf=31 -mvf=61 -dvf=60.114 -nnv
> Modeline "856x480" 33.27 856 880 896 1096 480 482 483 505 # 33 MHz, 30.4
> kHz, 60.1 Hz
>
> It turns out that only some resolutions are allowed; eg videogen -m=858x480
> won't work and gives
>
> argument 2 (-m=858x480) has an invalid parameter
>
> OK, now we have a modeline - time to use it.
>
> Edit your XF86 Config <http://www.mythtv.info/moin.cgi/F86Config>-4 file and
> find the Section "Monitor" part. Now simply insert the modeline generated
> above. Note the part in "s is the name of this mode.
>
> Now find the Section "Screen" part of the file. There should be a "Display"
> subsection and that should have a Modes line. This line contains a space
> seperated list of mode names - you cycle through these when you press *Ctrl
> Alt +* and *Ctrl Alt -* (that plus and minus keys) As always an example
> should make it easier:
>
> Section "Screen"
> Identifier "ProjScreen"
> Device "GeForce"
> Monitor "Projector"
> DefaultColorDepth 24
> DefaultFbbpp 32
> SubSection "Display"
> Depth 24
> FbBpp 32
> Modes "856x480"
> EndSubSection
> EndSection
>
>
>
> Now start X and you should have a shiny new mode.
>
> Useful Links:
>
>
> Linux HTPC How-to
>
> In particular this page:
>
> http://www.sllug.org/how-to/linux-htpc/video_card_configuration.html
> provides a useful overview.
>
>
> Videogen
>
> http://www.dynaweb.hu/opensource/videogen/
>
> It's similar to Powerstrip.
>
>
> A quick calculator
>
> http://www.hut.fi/Misc/Electronics/faq/vga2rgb/calc.html
>
> It needs Front & back porch and sync pulse info - I'm not sure what they are.
> Can I get this from the h/v frequency?
>
>
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