[mythtv-commits] Ticket #13618: Issue in macOS for playback of 480p/i videos on retina display

[MythTV]

#13618: Issue in macOS for playback of 480p/i videos on retina display
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 Reporter:  John Hoyt                |          Owner:  mark-kendall
     Type:  Bug Report - General     |         Status:  infoneeded
 Priority:  minor                    |      Milestone:  needs_triage
Component:  MythTV - Video Playback  |        Version:  v31-fixes
 Severity:  medium                   |     Resolution:
 Keywords:  MacOS VideoToolbox       |  Ticket locked:  0
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Comment (by mark-kendall):

 OK - progress of sorts:)

 Firstly, video mode switching is accessed through
 'Setup->Appearance->Separate video modes for GUI and TV playback'

 If you enable that, you should then be able to select 2560x1600 for the
 GUI. Then just select the same resolution for 'Video output', 'Auto' for
 rate and 'Default' for 'Aspect'. (Using anything else for video playback
 may just confuse the issue and is not required for this case - as the
 display is native 2560x1600 and has a variable display rate - so there is
 no benefit in trying to use other video modes).

 It would be interesting to see playback logs if that helps - though it is
 not a proper fix (it should work out of the box imho).

 So I think the root cause of the problem is this line from the Qt docs:-


 {{{
 Typically, most applications work with device independent pixels; except
 for OpenGL and code for raster graphics.
 }}}

 So with a retina display, the windowing system is using 1280x800 for the
 mythfrontend window/widget, and this is what Qt is using/reports, but the
 underlying OpenGL context will be using the native display size
 (2560x1600).

 The reason the HD video works and SD does not is not due to the different
 resolutions but because, in this case, the SD video is interlaced and the
 HD video is not. The mythtv opengl video code uses an intermediate
 framebuffer for deinterlacing (to improve performance) which triggers an
 OpenGL viewport change. The switch back to the regular/fullscreen viewport
 after deinterlacing is presumably where it all goes wrong - as the OpenGL
 context should be using 2560x1600 but is only set to 1280x800 (because
 that is the window size).

 If you go into the details of the video display profile
 (Setup->Video->Playback->Current video Playback Profile - and then into
 the specific profile details) and disable all deinterlacing, playback
 *should* work.

 The real head scratcher here, however, is why does the GUI work without
 issue? I note you said that sometimes it starts displaying in the bottom
 left and then reverts. Based on the assumption that the windowing system
 and OpenGL are using different resolutions, I don't honestly understand
 how it ever gets it right:)

 I can only assume that there is some event received, perhaps after our
 window is setup, that triggers a change.

 I'll pull together a debugging patch to see what is going on.

 Longer term, we need a fix that works out of the box, regardless of system
 settings etc. Personally I don't think we want to be using a downscaled UI
 at all - if you are playing HD/4k material, it will just be unnecessarily
 downscaled - and then scaled up again by the OS; which is far from ideal.

 Ideally we want to try and encourage/ensure Qt starts up with 2560x1600
 (or the proper native resolution at least). I really want to avoid having
 to add workarounds for scaling factors etc (i.e. using
 https://doc.qt.io/qt-5/qwindow.html#devicePixelRatio).

 What setting are you using for you macbook display?
 (https://support.apple.com/en-us/HT202471)

-- 
Ticket URL: <https://code.mythtv.org/trac/ticket/13618#comment:7>
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