[Openchrome-users] interleave problem with openchrome driver with SP8000 and TV out

[druyts pascal]

Thanks Ivor,
I will try to enable the deflickering and report on the results.

I still don't understand why the image is flickering and why deflickering is 
needed. If the image to display has no shift between even and odd lines, why 
should it flicker?

Could you explain what deflickering is doing? You say it would blur the 
picture, so I guess it averages somehow upper and lower frames.

I understand that an image could flicker if the frames are swapped at 
display. I mean, if the frames to display are [L1-U1] [L2-U2] ... and the 
driver outputs [U1-L2] [U2-L3] ... instead where L1 and U1 are the upper and 
lower frame of the first image. The image [L1-U1] is smooth (unless there 
was a problem at the recording; it is normally shoot as a single image by 
the camera and split in two frames after--this only olds for PAL coding).  
On the contrary, the image  [U1-L2] exhibits discontinuities between even 
and odd lines, which are furthermore swapped. Displaying such image could 
indeed result in flickering that could be reduced by bluring the image. But 
this seems unnecessary as displaying  [L1-U1] would be much preferable.

Does my understanding of the origin of flickering make sense? Is the TV 
output generated from a single buffer containing the full picture or are 
there two buffers, one for the upper and one for lower frames that could be 
somehow swapped?

Thanks,

Pascal

>On Monday 28 November 2005 15:13, druyts pascal wrote:
>>I noticed a strange distortion problem on the TV output on a epia SP8000.
>>The problem looks like an interleave problem, but the strange thing is 
>>that
>>the MPEG stream is not interleaved and does not present any distortion.
>>Even stranger, when pausing the movie, the image is flickering, I am not
>>sure of what is going on, but it could be that odd and even lines are
>>getting continuously swapped.
>>
>>I know that there are filters to reduce the inconvenience, but those 
>>filter
>>blur the image and load the CPU, which is already eavily loaded to play 
>>the
>>MPEG stream. My understanding is that those filters should only have to be
>>used if the original stream has been badly recorded.
>>
>>I also tested the via driver (which  needed minor modifications to compile
>>with a 2.6.13 kernel). With that driver, the "interleave" problem does not
>>show up and I therefore attribute the problem to the openchrome driver.
>>Unfortunetely, the via driver also has  a problem, some pixels --say 5 to
>>10 neighbouring pixels one or several horizontal line, but not always the
>>same--- have a bad color (usualy dark), as if  the buffer being unreadable
>>when the graphic card needs it (because it is accesed by the driver? I
>>don't know much about the driver implementation, don't flame me if this
>>hypothesis is stupid).
>>
>>I am using MythTV with the last svn version of the openchrome driver, XvMC
>>is not enabled (I understood I have to recompile MythTV with XvMCPro
>>enabled to test the HW acceleration) and the ouput is on a PAL TV.
>>
>>As a conclusion, the output of the via driver is more pleasant than that 
>>of
>>the openchrome drive, but also shows some problem. I would however prefer
>>to use the openchrome driver, beacuse it is open source of course, but 
>>also
>>because it is , if I understood well,  my only chance to use the hardware
>>mpeg decoding in MythTV because Myth does not support  the VeXP extension.
>>
>>Any idea on how I could resolve this "interleave" problem?
>>
>Hi,
>
>FYI the VIA driver defaults to using an excessive output hardware deflicker 
>filter. This will result in a picture that does not flicker at all. But if 
>you are outputting to a high quality screen you will notice an excessively 
>blurred picture.
>You can enable this hardware flicker filter on the openchrome driver by 
>using the "TVDeflicker" option and then you can compare the output.
>
>If you are outputting to an interlaced PAL TV, however, you will get the 
>best video picture image with flicker filter disabled and using a bob 
>deinterlacing method.
>You will still perceive flickering on non video images (i.e. menus and 
>such) unless they are "tuned" by the artist who created them for output on 
>a TV.
>
>Cheers,
>
>--
>Ivor Hewitt.

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