[mythtv] Playback next steps

Mark Kendall mark.kendall at gmail.com
Mon Dec 17 20:20:57 UTC 2018

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.

More information about the mythtv-dev mailing list