[mythtv] Kernel 2X HW-GL Deinterlacing

Peter Bennett pb.mythtv at gmail.com
Sat Nov 24 15:31:49 UTC 2018

On 11/23/18 5:48 PM, Mark Spieth wrote:
> On 11/24/2018 8:53 AM, David Engel wrote:
>> This issue was discussed on IRC some weeks ago but never resolved.  I
>> thought I'd bring it up here in hopes of resolving it.
>> On the Nvidia Shield, the kernel 2X HW-GL deinterlacer looks terrible
>> by default.  However, after explicitly setting the scan type to
>> "interlaced (reversed)", it clears up very nicely.  I don't see this
>> same behavior on Linux.  In fact, I don't see any difference among
>> the detect, interlaced (normal) and interlaced (reversed) scan types
>> on Linux but my vision isn't the best.
> I have seen this too. I believe it is gl/gles driver implementation 
> dependent.
> Ive also seen this on windows (laptops esp.)
> The GL interleavers need to perform the deinterleaving algo first and 
> the last step also inverts the image. GL coord system has 0,0 at 
> bottom left which mean the line order is reversed too so the 2nd field 
> is originally on the first line.
> I dont know if there is any way to tell its behaviour from an API 
> call. I suspect not.
> This ordering can be tweeked for android or runtime selectable.
> I noticed similar things for YV12 where the color was line swapped and 
> looked weird in one of the samples your provided. Easier to see on a 
> low res video.
> I have mods that I havent pushed which I have distributed in the past 
> and still use. I suspect something like this also as an impact on the 
> green line situation.
> Mark
>> Can anyone else confirm my findings, particularly on Linux? More
>> importantly, can anyone explain the observed behavior?  I know one
>> difference is the Shield uses OpenGL ES and Linux uses full OpenGL.
>> Does the Raspberry Pi use OpenGL ES, and if so, how does kernel 2x
>> HW-GL perform on it?
>> This is of interest because, in theory, kernel deinterlacing should be
>> better than linear blend deinterlacing.  Getting it working correctly
>> without having to set the scan type manually every time would be a
>> nice improvement.
>> David
I have found that kernel deinterlacing has not worked well on Linux or 
android, and I stick with linear blend. I tried the kernel deinterlace 
on the fire stick and it looks the same whether I have interlaced normal 
or interlaced reversed. In both cases there is a quivering effect on 
straight lines, worse than when using bob. Linear blend looks best in 
all cases. What type of effect do you see?


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