Status of MPEG-4 Part 2 (H.263) support in VA-API

Hi there!

This is not a bug report. This is more a technical question regarding the current status of the MPEG-4 **Part 2** standard in VA-API. As everybody knows, MPEG-4 Part 2 is the base of the once well-known Xvid and DivX codecs. ;-)

The MPEG-4 Part 2 standard was originally not included in VA-API. While several Linux howtos still describe it as "not supported" by VA-API, it is listed at other website, like Wikipedia, as supported. Unfortunately the libva NEWS document doesn't bring in this topic any clarity either.

So, what is the current status regarding the support of the MPEG-4 Part 2 (H.263) standard in VA-API (as of January 2021)?

I should clarify this question that I don't mean any "workaround implementation". A such one exits for example in the Mesa Gallium drivers. (On these it is possible enforce MPEG-4 Part 2 support with value `VAAPI_MPEG4_ENABLED=true`.)