[mythtv-users] Re: Custom Modeline
Cory Papenfuss
papenfuss at juneau.me.vt.edu
Mon Jul 19 12:50:33 EDT 2004
I don't have a PVR-350, so I haven't looked into it. I know the NVIDIA
crowd talks about TVOverscan Options and such... if the PVR-350 has that, it'd
be a better way to go.
Unless it's got some weird div/16 requirements (some cards have modes
that won't go because they must be evenly divisible by 8 or 16, or have nice
dotclocks, etc), you should be able to change visual resolutions without
changing the raster size resolution. I more or less mentioned that a few posts
back.
Your original line:
ModeLine "720x480" 34.563 720 752 840 928 480 484 488 504 -HSync -VSync
(difference between numbers) 32 88 88 4 4 16
... can be set to underscan to 624x440 (96 less H, 40 less v... take 48 off
each side, and 20 off both top and bottom):
ModeLine "624x440" 34.563 624 704 792 928 440 464 468 504 -HSync -VSync
80 88 136 24 4 36
The raster specs:
34.563 dotclock,
Hsync width of 88 pixels, total of 928 dots
Vsync width of 4 lines, total of 504 lines
stay the same... just "letterboxing" the picture to a smaller size. It's
crude, but it's practically guaranteed to work (unless the card can't be
programmed to that line for above mentioned or other reasons).
-Cory
*************************************************************************
* The prime directive of Linux: *
* - learn what you don't know, *
* - teach what you do. *
* (Just my 20 USm$) *
*************************************************************************
On Mon, 19 Jul 2004, Jim Sager wrote:
> Cory,
>
> Excuse my ignorance with respect to modelines. I have read through the
> discussion here and I have a question regarding underscanning the PVR-350
> TV-Out - can it be done using the modeline settings? Basically this is the
> setting that I currently have (found in myth setup documentation):
>
> Section "Monitor"
> Identifier "NTSC Monitor"
> HorizSync 30-68
> VertRefresh 50-120
> Mode "720x480"
> # D: 34.563 MHz, H: 37.244 kHz, V: 73.897 Hz
> DotClock 34.564
> HTimings 720 752 840 928
> VTimings 480 484 488 504
> Flags "-HSync" "-VSync"
> EndMode
> EndSection
>
> I currently have myth set to reduce the display size to 624x440 in order to
> fit in the TV screen (also have it running in a window since the x and y
> offsets don't appear to work unless you do so). Can the modeline settings be
> used to reduce the size of the visible picture and produce the correct offset
> to center it on the screen? I am truly showing my ignorance here with respect
> to modeline settings as well as an understanding of the hardware that's
> involved.
>
> Thanks,
> Jim
>
> On Friday 16 July 2004 07:50 am, Cory Papenfuss wrote:
>> It's certainly not the fault of the modelines that the TV is
>> overscanned. Rather, it's that historically TV pictures have always been
>> overscanned and the switch to HDTV apparently hasn't fixed that (?). If
>> you raster the specified visual resolution with the standard timings, the
>> picture will be overscanned. Since you (and I for that matter) are
>> essentially driving the TV directly from the VGA port, it's *REQUIRED* to
>> output an ATSC standard video signal raster with standard timings. If
>> you're TV is tolerant of something other than that, great... but make sure
>> it is by the book or you can blow it up.
>>
>> With all that said, remember that although the spec might specify
>> visual size (e.g. 1920x1080) in addition to the raster size/speed, it's the
>> raster that must be correct to avoid TV damage. Think of the raster as the
>> black canvas that's painted at a certain rate consisting of a certain
>> number of lines. For illustrative purposes, I scoured the 'net and found a
>> 1080i modeline that does appear to have a 33.75kHz horizonal frequency
>> (that appears to the be correct standard rate for 1080i... 45kHz for 720p
>> BTW):
>>
>> Modeline "1080i" 74.250 1920 2008 2048 2200 1080 1084 1094 1125 interlace
>>
>> You could use the same modeline, but have a letterboxed 1024x768
>> *visual* (upper left hand corner) by modifying it as follows:
>> Modeline "test" 74.250 1024 2008 2048 2200 768 1084 1094 1125 interlace
>>
>> Or try to move it towards the center by 200 pixels H/V:
>> Modeline "test" 74.250 1024 1808 1848 2200 768 884 894 1125 interlace
>>
>> In all those cases, the oscillators in the TV won't change at all...
>> just when and for how long the video guns turn pixels on and off.
>>
>> So if you are trying to vertically "underscan" the mode and can live
>> with running a "standard" HDTV raster with a "nonstandard" HDTV
>> visual resolution,
>>
>> Modeline "test2" 74.250 1920 2008 2048 2200 980 1034 1044 1125 interlace
>>
>> will keep the TV happy, and you should have a 1920x980 resolution, with 50
>> additional black pixels on both the top and the bottom. Although it's a
>> funky resolution, playing video on a linux box usually uses XV for scaling
>> anyway, so it usually scales to fit accordingly. If you're trying to
>> actually play all 1080 lines of a bone-fide 1080i orginal source material
>> without losing any lines off the screen, you'll need more than a
>> modeline.... like a TV fancy enough to adjust the screen position, or
>> unfancy enough to take a screwdriver to it and adjust the raster.
>>
>> Cheers
>> -Cory
>>
>>
>> *************************************************************************
>> * The prime directive of Linux: *
>> * - learn what you don't know, *
>> * - teach what you do. *
>> * (Just my 20 USm$) *
>> *************************************************************************
>>
>> On Thu, 15 Jul 2004, Chris Vargas wrote:
>>> Cory: your initial reply to John caught my eye,
>>> because I'm in John's same boat. At first I thought
>>> I'd be able to correct it given your great explanation
>>> of modelines, but now I'm not so sure.
>>>
>>> I have a 9A60 transcoder (thanks yet again, Jarod!),
>>> and am trying to adjust the vertical dimension as
>>> well. My 480p modeline plays back anamorphic DVDs
>>> correctly, but my 540p and 1080i modelines (derived
>>> via Powerstrip) are all stretched too far vertically,
>>> so that an anamorphic test pattern displays circles as
>>> ovals.
>>>
>>> Wouldn't I need to add vertical lines to get this
>>> compression? I tried using one of your examples to add
>>> (say) 40 pixels vertically, but if it's not going to
>>> work and blow up my TV, maybe not. Then again, it's 3
>>> years old and doesn't do 720p, so maybe I should blow
>>> it up...
>
> --
> jim
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