MVC: fix subtitle scaling

[samnazarko]

Description

This fixes the appearance of subtitles when playing back 3D MVC content and outputting it as Frame Packed.

Motivation and Context

Subtitles would not scale correctly before.
This should be backported to Leia.

How Has This Been Tested?

Tested on Raspberry Pi and Vero 4K +
(MMAL & AMCodec).

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed

[samnazarko]

Unless there are any objections, I'd like to get this in.
CC @popcornmix

[afedchin]

IMO this hack must be removed at all, I see no reason to support this tab/sbs subtitles.

[popcornmix]

I wonder if this was a better solution: #8254

[phunkyfish]

@samnazarko have you tried #8254?

[TheMontezuma]

I would really appreciate to have this bug fix integrated.
I use LibreElec with Raspberry Pi 3 and subtitles are often wrongly scaled/positioned when watching 3D MVC videos...

[TheMontezuma]

I tested this commit on RPI and it does not work

[DaveTBlake]

@samnazarko no idea if this is still relevent. I have bumped to v20 in case you want to pursue, but please close (and set milestone to abandoned) if not. Thanks

[samnazarko]

It's still relevant -- but the priority is low, as MVC 3D support was always supported with downstream out of tree patches.

This patch works for us on Vero 4K/4K+ (we can keep downstream for now); but a user reported it as not working on Pi.
When/if Pi's V4L2/GBM approach implements 3D MVC, we can revisit.

Cheers

[fuzzard]

@samnazarko another year on, whats the consensus on this?

[samnazarko]

I will check internally. We still use this downstream, to my knowledge.

[samnazarko]

It makes sense to merge this PR.

[samnazarko]

I'm going to merge this.