Fixes segfaults when handling files with odd chroma subsampled dimensions in some scenarios like using the hstack filter.
The sidebar allows multiple-selection, do DnD should also work.
I could not find any documentation which disallows the use of transparency for pixel formats other than YUV 4:2:0, so this patch adds support for transparency using 4:2:2, 4:4:4, RGB, and their high bit depth variants. It is not quite clear if the alpha channel should be encoded using the same pixel format as the normal channels, or it should be always YUV 4:2:0.
Priming samples don't depend on the contents of the first frame passed to the encoder but rather on encoder configuration, so use dummy vorbis_dsp_state and
Similar to the VMX backend [1], enable selective CR0 write intercept in the SVM backend to force CR0_ET/CR0_NE to 1, and CR0_CD/CR0_NW to 0. This addresses the severe performance issue observed in UEFI guests [2].