video: add alpha type metadata

This is mostly for testing. It adds passing through the metadata through
the video chain. The metadata can be manipulated with vf_format. Support
for zimg alpha conversion (if built with zimg after it gained alpha
support) is implemented. Support premultiplied input in vo_gpu.

Some things still seem to be buggy.

1 files changed, 7 insertions, 0 deletions

diff --git a/video/csputils.c b/video/csputils.c
index cc9aa4d64a..ef26813af0 100644
--- a/video/csputils.c
+++ b/video/csputils.c
@@ -108,6 +108,13 @@ const struct m_opt_choice_alternatives mp_chroma_names[] = {
     {0}
 };
 
+const struct m_opt_choice_alternatives mp_alpha_names[] = {
+    {"auto",        MP_ALPHA_AUTO},
+    {"straight",    MP_ALPHA_STRAIGHT},
+    {"premul",      MP_ALPHA_PREMUL},
+    {0}
+};
+
 void mp_colorspace_merge(struct mp_colorspace *orig, struct mp_colorspace *new)
 {
     if (!orig->space)