How do I get 23.976Hz?

[lixe86]

Hello,
I'm new to Linux and use it at the moment only for XBMC. Everything works fine so far, but I want to have 23.976Hz instead of 24Ht. In the nVidia config I can only choose 24Hz, 50Hz and 60Hz.

Here is my xorg.conf:

# nvidia-settings: X configuration file generated by nvidia-settings
# nvidia-settings: version 1.0 (buildmeister@builder63) Fri Apr 3 13:02:44 PST 2009

Section "ServerLayout"
Identifier "Layout0"
Screen 0 "Screen0" 0 0
InputDevice "Keyboard0" "CoreKeyboard"
InputDevice "Mouse0" "CorePointer"
EndSection

Section "Files"
EndSection

Section "Module"
Load "dbe"
Load "extmod"
Load "type1"
Load "freetype"
Load "glx"
EndSection

Section "ServerFlags"
Option "Xinerama" "0"
EndSection

Section "InputDevice"
# generated from default
Identifier "Mouse0"
Driver "mouse"
Option "Protocol" "auto"
Option "Device" "/dev/psaux"
Option "Emulate3Buttons" "no"
Option "ZAxisMapping" "4 5"
EndSection

Section "InputDevice"
# generated from default
Identifier "Keyboard0"
Driver "kbd"
EndSection

Section "Monitor"
# HorizSync source: xconfig, VertRefresh source: xconfig
Identifier "Monitor0"
VendorName "Unknown"
ModelName "SONY TV"
HorizSync 15.0 - 68.0
VertRefresh 23.0 - 61.0
Option "DPMS"
EndSection

Section "Device"
Identifier "Device0"
Driver "nvidia"
VendorName "NVIDIA Corporation"
BoardName "GeForce 9400 GT"
EndSection

Section "Screen"
Identifier "Screen0"
Device "Device0"
Monitor "Monitor0"
DefaultDepth 24
Option "TwinView" "0"
Option "metamodes" "nvidia-auto-select +0+0; 1920x1080_60 +0+0"
SubSection "Display"
Depth 24
EndSubSection
EndSection

Maybe someone can explain me what I have to change to get 23.976Hz =)

[hl_]

Are you trying to achieve exactly the same refresh frequency as some video files? This probably won't work.

[lixe86]

Yes I'm trying that =)
Why shouldn't that work? Or would it be possible to get the same timings as the one I'm getting if I chooste 1080/24p in Windows nVidia Control Center? I checked them with Powerstrip and when I select 1080/24p I get the following:
PowerStrip timing parameters:

1920x1080=1920,638,44,148,1080,4,5,36,74129,512

Generic timing details for 1920x1080:
HFP=638 HSW=44 HBP=148 kHz=27 VFP=4 VSW=5 VBP=36 Hz=24

VESA detailed timing:
PClk=74,13 H.Active=1920 H.Blank=830 H.Offset=622 HSW=44 V.Active=1080 V.Blank=45 V.Offset=4 VSW=5

Linux modeline parameters:
"1920x1080" 74,129 1920 2558 2602 2750 1080 1084 1089 1125 +hsync +vsync

So it would also be enough to get these ones under Linux? But I don't have any Idea how to do that.

[lixe86]

Ok I just cchecked the timings using Windows and Powerstrip. Here are the ones I wana use:
ModeLine "1920x1080@23" 74,129 1920 2558 2602 2750 1080 1084 1089 1125 +hsync +vsync
ModeLine "1920x1080@24" 74,250 1920 2558 2602 2750 1080 1084 1089 1125 +hsync +vsync
ModeLine "1920x1080@50" 148,500 1920 2448 2492 2640 1080 1084 1089 1125 +hsync +vsync
ModeLine "1920x1080@60" 148,500 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync

But everytime I add them to my xorg.conf following http://www.wilsonet.com/mythtv/mythhd.php I just get a popup window with a yellow warning triangle and some crazy letters. When I remove the ModeLine lines and reboot, everything works fine again except I don't have 23.976Hz...

[jyavenard]

Hi

I was in the same situation as you.
I got my nvidia card to do all the refresh rates commonly encountered:
23.976Hz, 24Hz, 50Hz, 59.94Hz, 60Hz

http://www.avenard.org/media/Patches...esh_rates.html

[sfer]

I finally got 23.976 fps vsynced video running properly after ditching xv and using opengl and a few tricks. My tv currently runs at 23.97 Hz according to nvidia-settings when I choose 24 Hz from the settings. I'm not sure if it really is 23.976 and the application just rounds it. Anyway, I still get occasional, periodic (or so it seems) frame skips so I thought I might try to get exactly 23.976.

How would I use those modelines when my tv is the secondary monitor and not listed in xorg.conf? Only my primary monitor is, and as far as I understood it's for the same reason that X only sees one because of the way Twinview works. Is there no other way than changing the tv to be my primary display? That would place the KDE panels and other stuff over there instead of the desktop monitor where I want everything except movies and occasional games to be.

[Steve Cave]

I have also found that completely smooth playback requires that the ratio between monitor refresh rate and video framerate be an integer. Thus, when playing 23.976 fps content, I use a 72 Hz video mode and play the content at 24 fps to achieve smooth playback.

[lixe86]

Ok, finally I got it working, but I still have A/V sync issues. How is that possible. If I play a video with 23.976 fps at 23.976Hz the playback should be synchronic, shouldn't it? I'm using XBMC, maybe that's the problem?

[jyavenard]

One issue to keep in mind is that there's an underlying bug in the nvidia drivers .

If the framerate matches exactly the display refresh rate, when using Xv to render video, X will take 100% of the CPU time and playback will be jerky

[lixe86]

Can I do something against that? If I choose 60Hz everything works really fine, but of course it would be nicer too have 24p playback. So what should I do? Is there something else I cloud try or should I just use 60Hz?

[sfer]

I worked around the xv issue by using gl output with -framedrop and -autosync n, n > 0 to prevent audio sync drift and weird occasional tearing at the top of the screen. I've not done through testing on the autosync parameter but a value of 2 seems to work fine.

All that's left to fix is getting the exact refresh rate on a secondary monitor. (Anyone?)

[pgs]

Originally Posted by lixe86

Ok, finally I got it working, but I still have A/V sync issues. How is that possible. If I play a video with 23.976 fps at 23.976Hz the playback should be synchronic, shouldn't it? I'm using XBMC, maybe that's the problem?

Because the audio and video could be (or they always are) asynchronous.

If the audio is 48000Hz or 44100Hz, they will not have any integer ratio with a video frame rate of 23.976Hz, so one frame worth of data may contain different amount of audio (which could still be OK).

In addition to this, the audio card can be completely un-synchronized with the video output.

So trying to keep the correct audio rate and video rate together might be difficult.

This is why the frame drop/repeat mechanism is implemented in many video backends. Basically the audio runs at its own rate and the video tries to follow. If it is too fast, frame drop occurs, if it is too slow, frame repeat.

Of course, another option would be to resample properly the audio, but this might be to expensive.
Or to use one single common clock to derive all timings, which might not be feasible on a PC (each peripheral seems to have its own clock).

In this situation, 24Hz or 23.976Hz are, basically, the same.

pgs