Add support for VP8/VP9 codecs (usually via media-libs/libvpx)

Packages describing “vpx” as local USE flag

Package“vpx” Flag Description
media-tv/tvheadendEnable transcoding with the VP8/VP9 video codecs
media-video/ffmpegEnable VP8 and VP9 de/encoding support via media-libs/libvpx in addition to FFmpeg's own implementation (for decoding only)
media-video/ffmpeg-compatEnable VP8 and VP9 de/encoding support via media-libs/libvpx in addition to FFmpeg's own implementation (for decoding only)

All packages providing a “vpx” USE flag (15)