VTB on OSX: fix flickering video caused by buffer overwrite

[FernetMenta]

see title. This applies the same concept we already have for vdpau and vaapi.

[mention-bot]

@FernetMenta, thanks for your PR! By analyzing the history of the files in this pull request, we identified @afedchin, @davilla and @Memphiz to be potential reviewers.

[FernetMenta]

@Memphiz I think iOS has the same issue. There you could use the standard functions glFenceSync that are available for GLES.

[FernetMenta]

jenkins build this please

[MartijnKaijser]

jenkins build this please (github died for awhile)

[MartijnKaijser]

ignore the win32 fail

[Memphiz]

Nice - great work - thx - so thats the fix for the stuttering issue?

[FernetMenta]

@Memphiz "stuttering" is not the right term if you mean this case: http://forum.kodi.tv/showthread.php?tid=281517

"choppy" is better suited here. But since there a always multiple definitions out there, I requested a video for better diagnosis :)

jenkins build this please

[MrMC]

might want to check the ref count on m_vtbbuf, vda/vtb will not re-use it if greater than one.

[popcornmix]

glFenceSync is GLES3 only, not GLES2:
https://www.khronos.org/opengles/sdk/docs/man3/html/glFenceSync.xhtml

[FernetMenta]

might want to check the ref count on m_vtbbuf, vda/vtb will not re-use it if greater than one.

that is not the problem here

[MrMC]

ok mr.expert :)