Better support for fractional framerates

Author: ns6089

src/Limelight.h

@@ -76,7 +76,7 @@ typedef struct _STREAM_CONFIGURATION {
 
     // If specified, the client's display refresh rate x 100. For example,
     // 59.94 Hz would be specified as 5994. This is used by recent versions
-    // of GFE for enhanced frame pacing.
+    // of GFE for enhanced frame pacing. Ignored by Sunshine.
     int clientRefreshRateX100;
 
     // If specified, sets the encoder colorspace to the provided COLORSPACE_*
@@ -100,11 +100,23 @@ typedef struct _STREAM_CONFIGURATION {
     // in /launch and /resume requests.
     char remoteInputAesKey[16];
     char remoteInputAesIv[16];
+
+    // Fractional frame rate of the video stream (in the form of numerator
+    // and denominator). Supported by recent versions of Sunshine.
+    // The non-fractional frame rate still needs to be specified for backward
+    // compatibility. LiConvertFloatingPointFrameRateToFraction() can be used for
+    // converting floating-point frame rates to this representation.
+    int fpsNum;
+    int fpsDen;
 } STREAM_CONFIGURATION, *PSTREAM_CONFIGURATION;
 
 // Use this function to zero the stream configuration when allocated on the stack or heap
 void LiInitializeStreamConfiguration(PSTREAM_CONFIGURATION streamConfig);
 
+// Use this function to convert floating-point frame rates to fractional frame
+// rates (in the form of numerator and denominator) while trying to maximize precision.
+void LiConvertFloatingPointFrameRateToFraction(double value, int* outNum, int* outDen);
+
 // These identify codec configuration data in the buffer lists
 // of frames identified as IDR frames for H.264 and HEVC formats.
 // For other codecs, all data is marked as BUFFER_TYPE_PICDATA.

src/Misc.c

@@ -1,5 +1,7 @@
 #include "Limelight-internal.h"
 
+#include <math.h>
+
 #define ENET_INTERNAL_TIMEOUT_MS 100
 
 // This function wraps enet_host_service() and hides the fact that it must be called
@@ -128,6 +130,33 @@ void LiInitializeStreamConfiguration(PSTREAM_CONFIGURATION streamConfig) {
     memset(streamConfig, 0, sizeof(*streamConfig));
 }
 
+void LiConvertFloatingPointFrameRateToFraction(double value, int* outNum, int* outDen) {
+    if (fabs(value) < 1.0) {
+        // Unrealistic scenario, we don't care about perfect precision
+        *outNum = round(INT32_MAX * value);
+        *outDen = INT32_MAX;
+    }
+    else if (fabs(value) > 1000.0) {
+        // Unrealistic scenario, we don't care about perfect precision
+        *outNum = INT32_MAX;
+        *outDen = round(INT32_MAX / value);
+    }
+    else {
+        // Try different numerators for the best precision
+        double maxError = 1.0;
+        for (int i = 0; i < value; ++i) {
+            int num = INT32_MAX - i;
+            int den = round(num / value);
+            double error = fabs((double)num / den - value);
+            if (error < maxError) {
+                maxError = error;
+                *outNum = num;
+                *outDen = den;
+            }
+        }
+    }
+}
+
 void LiInitializeVideoCallbacks(PDECODER_RENDERER_CALLBACKS drCallbacks) {
     memset(drCallbacks, 0, sizeof(*drCallbacks));
 }

src/SdpGenerator.c

@@ -309,6 +309,15 @@ static PSDP_OPTION getAttributesList(char*urlSafeAddr) {
         else {
             err |= addAttributeString(&optionHead, "x-ss-video[0].chromaSamplingType", "0");
         }
+
+        // Specify fractional frame rate if requested
+        if (StreamConfig.fpsNum > 0 && StreamConfig.fpsDen > 0) {
+            snprintf(payloadStr, sizeof(payloadStr), "%d", StreamConfig.fpsNum);
+            err |= addAttributeString(&optionHead, "x-ml-video.targetFrameRateNum", payloadStr);
+
+            snprintf(payloadStr, sizeof(payloadStr), "%d", StreamConfig.fpsDen);
+            err |= addAttributeString(&optionHead, "x-ml-video.targetFrameRateDen", payloadStr);
+        }
     }
 
     snprintf(payloadStr, sizeof(payloadStr), "%d", StreamConfig.width);