add experimental NV12 to IYUV conversion routine

src/frame_streams/sdl/video_push_converter.cpp

@@ -1,5 +1,7 @@
 #include "./video_push_converter.hpp"
 
+#include <cstring>
+
 SDL_Surface* convertYUY2_IYUV(SDL_Surface* surf) {
 	if (surf->format != SDL_PIXELFORMAT_YUY2) {
 		return nullptr;
@@ -56,3 +58,49 @@ SDL_Surface* convertYUY2_IYUV(SDL_Surface* surf) {
 	return conv_surf;
 }
 
+SDL_Surface* convertNV12_IYUV(SDL_Surface* surf) {
+	if (surf->format != SDL_PIXELFORMAT_NV12) {
+		return nullptr;
+	}
+	if ((surf->w % 2) != 0) {
+		SDL_SetError("NV12->IYUV does not support odd widths");
+		// hmmm, we dont handle odd widths
+		return nullptr;
+	}
+
+	SDL_LockSurface(surf);
+
+	SDL_Surface* conv_surf = SDL_CreateSurface(surf->w, surf->h, SDL_PIXELFORMAT_IYUV);
+	SDL_LockSurface(conv_surf);
+
+	// NV12 is planar Y and interleaved UV in 4:2:0
+	// Y is simple, we just copy it over
+	// U V are ... packed?
+
+	uint8_t* y_plane = static_cast<uint8_t*>(conv_surf->pixels);
+	uint8_t* u_plane = static_cast<uint8_t*>(conv_surf->pixels) + conv_surf->w*conv_surf->h;
+	uint8_t* v_plane = static_cast<uint8_t*>(conv_surf->pixels) + conv_surf->w*conv_surf->h + (conv_surf->w/2)*(conv_surf->h/2);
+
+	const uint8_t* nv12_y_plane = static_cast<const uint8_t*>(surf->pixels);
+	const uint8_t* nv12_uv_data = static_cast<const uint8_t*>(surf->pixels) + surf->w*surf->h;
+
+	// y can be copied as is
+	std::memcpy(
+		y_plane,
+		nv12_y_plane,
+		surf->w*surf->h
+	);
+
+	// we operate at half res
+	for (int y = 0; y < surf->h/2; y++) {
+		for (int x = 0; x < surf->w/2; x++) {
+			u_plane[y*(surf->w/2)+x] = nv12_uv_data[y*(surf->w/2)*2+x*2];
+			v_plane[y*(surf->w/2)+x] = nv12_uv_data[y*(surf->w/2)*2+x*2+1];
+		}
+	}
+
+	SDL_UnlockSurface(conv_surf);
+	SDL_UnlockSurface(surf);
+	return conv_surf;
+}
+

src/frame_streams/sdl/video_push_converter.hpp

@@ -21,6 +21,7 @@ static bool isFormatYUV(SDL_PixelFormat f) {
 }
 
 SDL_Surface* convertYUY2_IYUV(SDL_Surface* surf);
+SDL_Surface* convertNV12_IYUV(SDL_Surface* surf);
 
 template<typename RealStream>
 struct PushConversionVideoStream : public RealStream {
@@ -42,6 +43,8 @@ struct PushConversionVideoStream : public RealStream {
 				//auto end = Message::getTimeMS();
 				// 3ms
 				//std::cerr << "DTC: timing " << SDL_GetPixelFormatName(converted_surf->format) << "->SDL_PIXELFORMAT_IYUV: " << end-start << "ms\n";
+			} else if (surf->format == SDL_PIXELFORMAT_NV12 && _forced_format == SDL_PIXELFORMAT_IYUV) {
+				surf = convertNV12_IYUV(surf);
 			} else if (isFormatYUV(surf->format)) {
 				// TODO: fix sdl rgb->yuv conversion resulting in too dark (colorspace) issues
 				// https://github.com/libsdl-org/SDL/issues/10877