avcodec: add vlc_va_GetChroma() helper

modules/codec/avcodec/va.c

@@ -25,9 +25,50 @@
 
 #include <vlc_common.h>
 #include <vlc_modules.h>
+#include <vlc_fourcc.h>
+#include <libavutil/pixfmt.h>
 #include <libavcodec/avcodec.h>
 #include "va.h"
 
+vlc_fourcc_t vlc_va_GetChroma(enum PixelFormat hwfmt, enum PixelFormat swfmt)
+{
+    /* NOTE: At the time of writing this comment, the return value was only
+     * used to probe support as decoder output. So incorrect values were not
+     * fatal, especially not if a software format. */
+    switch (hwfmt)
+    {
+        case AV_PIX_FMT_VAAPI_VLD:
+            return VLC_CODEC_YV12;
+
+        case AV_PIX_FMT_DXVA2_VLD:
+            return VLC_CODEC_YV12;
+#if (LIBAVUTIL_VERSION_INT >= AV_VERSION_INT(53, 14, 0))
+        case AV_PIX_FMT_VDA_VLD:
+            return VLC_CODEC_UYVY;
+#endif
+#if (LIBAVUTIL_VERSION_INT >= AV_VERSION_INT(52, 4, 0))
+        case AV_PIX_FMT_VDPAU:
+            switch (swfmt)
+            {
+                case AV_PIX_FMT_YUVJ444P:
+                case AV_PIX_FMT_YUV444P:
+                    return VLC_CODEC_VDPAU_VIDEO_444;
+                case AV_PIX_FMT_YUVJ422P:
+                case AV_PIX_FMT_YUV422P:
+                    return VLC_CODEC_VDPAU_VIDEO_422;
+                case AV_PIX_FMT_YUVJ420P:
+                case AV_PIX_FMT_YUV420P:
+                    return VLC_CODEC_VDPAU_VIDEO_420;
+                default:
+                    return 0;
+            }
+            break;
+#endif
+        default:
+            return 0;
+    }
+}
+
 static int vlc_va_Start(void *func, va_list ap)
 {
     vlc_va_t *va = va_arg(ap, vlc_va_t *);

modules/codec/avcodec/va.h

@@ -42,6 +42,15 @@ struct vlc_va_t {
     int  (*extract)(vlc_va_t *, picture_t *pic, uint8_t *data);
 };
 
+/**
+ * Determines the VLC video chroma value for a pair of hardware acceleration
+ * PixelFormat and software PixelFormat.
+ * @param hwfmt the hardware acceleration pixel format
+ * @param swfmt the software pixel format
+ * @return a VLC chroma value, or 0 on error.
+ */
+vlc_fourcc_t vlc_va_GetChroma(enum PixelFormat hwfmt, enum PixelFormat swfmt);
+
 /**
  * Creates an accelerated video decoding back-end for libavcodec.
  * @param obj parent VLC object