[mythtv] Playback next steps

Mark Spieth mark at digivation.com.au
Mon Dec 17 21:07:09 UTC 2018

On 12/18/2018 7:40 AM, Peter Bennett wrote:
> On 12/17/18 3:20 PM, Mark Kendall wrote:
>> On Mon, 17 Dec 2018 at 16:20, Peter Bennett <pb.mythtv at gmail.com> wrote:
>>> I think it is actually about two thirds of the way across the screen 
>>> that it starts. Other details -
>>> The jaggies occur with both interlaced and progressive video.
>>> In file mythrender_opengl2es.h there is the line
>>> m_qualifiers = "precision highp float;\n";
>>> This was previously set as mediump - and the jaggies occurred on the 
>>> fire TV  and fire TV 4k.
>>> After I changed this to highp -
>>> On fire TV there was an error message that highp is not supported 
>>> and it is reverting to mediump, and the jaggies remain
>>> On fire TV 4K the jaggies went away and the picture is perfect
>> There is an ifdef that needs to go into the shaders - platforms that
>> support highp set a define. Should fix the error message.
>> I don't think there is a way around the sampling issue with the UYVY
>> code as it stands. Once precision is lost the shader starts to select
>> the wrong texture sample - and because 2 pixels are packed into one
>> sample, the sampling is highly inaccurate. It will be less obvious in
>> the other methods that don't use the extra packing  - but will still
>> be an issue.
>>> This is mostly way over my head, but it sounds good.
>>> My recommendation is that we should only commit this into master 
>>> after we have created the fixes/30 branch in January. The changes 
>>> sound major and they could potentially cause some unexpected issues 
>>> with some configurations. I would not want the users who install 
>>> from Ubuntu 19.04 to encounter problems.
>> I have a patch for the UYVY code ready to go. It will fix the
>> interlaced chroma issue and the precision problem. It is not at all
>> invasive. If OpenGLVideo currently works without YV12 or UYVY, it will
>> work after the change. It effectively removes the custom UYVY code. We
>> still use UYVY but it is not as densely packed - so there is a larger
>> texture in video memory but no sampling problem and no need for the
>> extra filter stage.
>> Regards
>> Mark
>> _______________________________________________
> Welcome back!
> It is OK with me if are confident and you want to commit it now. Let 
> us know when you have either a patch or have committed it so that I 
> can do some testing.

Looking forward to your GL insights Mark. It's very confusing when you 
dont have the model in your head.

I saw shader issues too but I never had the guts to commit changes. I am 
still running some android only local shader GL patches.


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