ffmpegdecoder: use real colorspace coefficients in shader

app/common/ffmpegutils.cpp

@@ -111,6 +111,28 @@ AVSampleFormat FFmpegUtils::GetFFmpegSampleFormat(const AudioParams::Format &smp
   return AV_SAMPLE_FMT_NONE;
 }
 
+int FFmpegUtils::GetSwsColorspaceFromAVColorSpace(AVColorSpace cs)
+{
+  switch (cs) {
+  case AVCOL_SPC_BT709:
+    return SWS_CS_ITU709;
+  case AVCOL_SPC_FCC:
+    return SWS_CS_FCC;
+  case AVCOL_SPC_BT470BG:
+    return SWS_CS_ITU624;
+  case AVCOL_SPC_SMPTE170M:
+    return SWS_CS_SMPTE170M;
+  case AVCOL_SPC_SMPTE240M:
+    return SWS_CS_SMPTE240M;
+  case AVCOL_SPC_BT2020_NCL:
+    return SWS_CS_BT2020;
+  default:
+    break;
+  }
+
+  return SWS_CS_DEFAULT;
+}
+
 AVPixelFormat FFmpegUtils::GetFFmpegPixelFormat(const VideoParams::Format &pix_fmt, int channel_layout)
 {
   if (channel_layout == VideoParams::kRGBChannelCount) {

app/common/ffmpegutils.h

@@ -24,6 +24,7 @@
 extern "C" {
 #include <libavcodec/avcodec.h>
 #include <libavformat/avformat.h>
+#include <libswscale/swscale.h>
 }
 
 #include "render/audioparams.h"
@@ -57,6 +58,14 @@ public:
    * @brief Returns an FFmpeg sample format type for a given native type
    */
   static AVSampleFormat GetFFmpegSampleFormat(const AudioParams::Format &smp_fmt);
+
+  /**
+   * @brief Returns an SWS_CS_* macro from an AVColorSpace enum member
+   *
+   * Why aren't these the same thing anyway? And for that matter, why doesn't FFmpeg provide a
+   * convenience function to do this conversion for us? Who knows, but here we are.
+   */
+  static int GetSwsColorspaceFromAVColorSpace(AVColorSpace cs);
 };
 
 using AVFramePtr = std::shared_ptr<AVFrame>;