Handle chroma co-siting in the Metal shaders

app/shaders/vt_renderer.metal

@@ -10,6 +10,7 @@ struct CscParams
 {
     float3 matrix[3];
     float3 offsets;
+    float2 chromaOffset;
     float bitnessScaleFactor;
 };
 
@@ -25,8 +26,10 @@ fragment float4 ps_draw_biplanar(Vertex v [[ stage_in ]],
                                  texture2d<float> luminancePlane [[ texture(0) ]],
                                  texture2d<float> chrominancePlane [[ texture(1) ]])
 {
+    float2 chromaOffset = float2(cscParams.chromaOffset.x / chrominancePlane.get_width(),
+                                 cscParams.chromaOffset.y / chrominancePlane.get_height());
     float3 yuv = float3(luminancePlane.sample(s, v.texCoords).r,
-                        chrominancePlane.sample(s, v.texCoords).rg);
+                        chrominancePlane.sample(s, v.texCoords + chromaOffset).rg);
     yuv *= cscParams.bitnessScaleFactor;
     yuv -= cscParams.offsets;
 
@@ -43,9 +46,13 @@ fragment float4 ps_draw_triplanar(Vertex v [[ stage_in ]],
                                   texture2d<float> chrominancePlaneU [[ texture(1) ]],
                                   texture2d<float> chrominancePlaneV [[ texture(2) ]])
 {
+    float2 chromaOffsetU = float2(cscParams.chromaOffset.x / chrominancePlaneU.get_width(),
+                                  cscParams.chromaOffset.y / chrominancePlaneU.get_height());
+    float2 chromaOffsetV = float2(cscParams.chromaOffset.x / chrominancePlaneV.get_width(),
+                                  cscParams.chromaOffset.y / chrominancePlaneV.get_height());
     float3 yuv = float3(luminancePlane.sample(s, v.texCoords).r,
-                        chrominancePlaneU.sample(s, v.texCoords).r,
+                        chrominancePlaneU.sample(s, v.texCoords + chromaOffsetU).r,
-                        chrominancePlaneV.sample(s, v.texCoords).r);
+                        chrominancePlaneV.sample(s, v.texCoords + chromaOffsetV).r);
     yuv *= cscParams.bitnessScaleFactor;
     yuv -= cscParams.offsets;
 

app/streaming/video/ffmpeg-renderers/vt_metal.mm

@@ -31,6 +31,7 @@ struct CscParams
 struct ParamBuffer
 {
     CscParams cscParams;
+    vector_float2 chromaOffset;
     float bitnessScaleFactor;
 };
 
@@ -313,6 +314,40 @@ public:
                 paramBuffer.cscParams.matrix[i][2] *= uvScale;
             }
 
+            switch (frame->chroma_location) {
+            default:
+            case AVCHROMA_LOC_LEFT:
+                paramBuffer.chromaOffset[0] = 0;
+                paramBuffer.chromaOffset[1] = 0.5;
+                break;
+            case AVCHROMA_LOC_CENTER:
+                paramBuffer.chromaOffset[0] = 0.5;
+                paramBuffer.chromaOffset[1] = 0.5;
+                break;
+            case AVCHROMA_LOC_TOPLEFT:
+                paramBuffer.chromaOffset[0] = 0;
+                paramBuffer.chromaOffset[1] = 0;
+                break;
+            case AVCHROMA_LOC_TOP:
+                paramBuffer.chromaOffset[0] = 0.5;
+                paramBuffer.chromaOffset[1] = 0;
+                break;
+            case AVCHROMA_LOC_BOTTOMLEFT:
+                paramBuffer.chromaOffset[0] = 0;
+                paramBuffer.chromaOffset[1] = 1.0;
+                break;
+            case AVCHROMA_LOC_BOTTOM:
+                paramBuffer.chromaOffset[0] = 0.5;
+                paramBuffer.chromaOffset[1] = 1.0;
+                break;
+            }
+
+            if (m_VideoFormat & VIDEO_FORMAT_MASK_YUV444) {
+                // 4:4:4 has no subsampling
+                paramBuffer.chromaOffset[0] = 0;
+                paramBuffer.chromaOffset[1] = 0;
+            }
+
             // Set the EDR metadata for HDR10 to enable OS tonemapping
             if (frame->color_trc == AVCOL_TRC_SMPTE2084 && m_MasteringDisplayColorVolume != nullptr) {
                 m_MetalLayer.EDRMetadata = [CAEDRMetadata HDR10MetadataWithDisplayInfo:(__bridge NSData*)m_MasteringDisplayColorVolume
@@ -676,6 +711,7 @@ public:
 
         m_Window = params->window;
         m_FrameRateRange = CAFrameRateRangeMake(params->frameRate, params->frameRate, params->frameRate);
+        m_VideoFormat = params->videoFormat;
 
         id<MTLDevice> device = getMetalDevice();
         if (!device) {
@@ -972,6 +1008,7 @@ private:
     id<MTLCommandQueue> m_CommandQueue;
     id<MTLTexture> m_SwMappingTextures[MAX_VIDEO_PLANES];
     SDL_MetalView m_MetalView;
+    int m_VideoFormat;
     int m_LastColorSpace;
     bool m_LastFullRange;
     int m_LastFrameWidth;