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, 4 insertions, 2 deletions

diff --git a/video/out/gpu/video.c b/video/out/gpu/video.c
index 9d5df7c739..4d14eb8019 100644
--- a/video/out/gpu/video.c
+++ b/video/out/gpu/video.c
@@ -2357,9 +2357,11 @@ static void pass_convert_yuv(struct gl_video *p)
     p->components = 3;
     if (!p->has_alpha || p->opts.alpha_mode == ALPHA_NO) {
         GLSL(color.a = 1.0;)
-    } else { // alpha present in image
+    } else if (p->image_params.alpha == MP_ALPHA_PREMUL) {
         p->components = 4;
-        GLSL(color = vec4(color.rgb * color.a, color.a);)
+    } else {
+        p->components = 4;
+        GLSL(color = vec4(color.rgb * color.a, color.a);) // straight -> premul
     }
 }