vpx encoding support

[Antoine Martin]

the vpx api is almost identical to x264 so this is easy to add, the patch almost works but I must be doing something wrong with the packing/index of the channels

[Antoine Martin]

vpx almost working

[Antoine Martin]

please take a look, I am sure you can figure out what I did wrong quickly

note: when merging the x264 and vpx codepaths can be merged (in server.py and window_backing.py), only the implementation class is different (and the dimensions rounding - but this can also be moved to a codec class attribute).

[ahuillet]

• Your mask for window size is incorrect - should be FFFE to ensure even dimensions, FFFF just truncates it to < 65535.
• Are you sure that libvpx can do the RGB -> YUV420 colorspace conversion by itself? You're allocating an input picture in YUV420 format but filling it in with RGB packed data (hence a single plane)
• Same on the decompress side: the codec probably works with YUV420 (or any other form of YUV), but your output should be RGB

[Antoine Martin]

• the mask is OK, vpx does not seem to mind odd dimensions, I left the mask code in to make it easier to merge the x264 and vpx code together
• rgb-yuv: yes, obviously.. that did the trick

r677 fixes the colourspace and vpx is now supported (also refactored the x264 code to re-use as much code as possible)

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/97