vo_opengl: handle chroma location

Use the video decoder chroma location flags and render chroma locations
other than centered. Until now, we've always used the intuitive and
obvious centered chroma location, but H.264 uses something else.

FFmpeg provides a small overview in libavcodec/avcodec.h:

-----------
/**
 *  X   X      3 4 X      X are luma samples,
 *             1 2        1-6 are possible chroma positions
 *  X   X      5 6 X      0 is undefined/unknown position
 */
enum AVChromaLocation{
    AVCHROMA_LOC_UNSPECIFIED = 0,
    AVCHROMA_LOC_LEFT        = 1, ///< mpeg2/4, h264 default
    AVCHROMA_LOC_CENTER      = 2, ///< mpeg1, jpeg, h263
    AVCHROMA_LOC_TOPLEFT     = 3, ///< DV
    AVCHROMA_LOC_TOP         = 4,
    AVCHROMA_LOC_BOTTOMLEFT  = 5,
    AVCHROMA_LOC_BOTTOM      = 6,
    AVCHROMA_LOC_NB             , ///< Not part of ABI
};
-----------

The visual difference is literally minimal, but since videophiles
apparently consider this detail as quality mark of a video renderer,
support it anyway. We don't bother with chroma locations other than
centered and left, though.

Not sure about correctness, but it's probably ok.

1 files changed, 3 insertions, 0 deletions

diff --git a/video/mp_image.h b/video/mp_image.h
index 643b70b949..96b980039d 100644
--- a/video/mp_image.h
+++ b/video/mp_image.h
@@ -43,6 +43,7 @@ struct mp_image_params {
     int d_w, d_h;               // define display aspect ratio (never 0/0)
     enum mp_csp colorspace;
     enum mp_csp_levels colorlevels;
+    enum mp_chroma_location chroma_location;
 };
 
 /* Memory management:
@@ -90,6 +91,8 @@ typedef struct mp_image {
 
     enum mp_csp colorspace;
     enum mp_csp_levels levels;
+    enum mp_chroma_location chroma_location;
+
     /* only inside filter chain */
     double pts;
     /* memory management */