Allow encoder to pick optimal ref frame count if RFI is supported by the decoder

src/Limelight-internal.h

@@ -76,6 +76,7 @@ extern SS_PING VideoPingPayload;
 int serviceEnetHost(ENetHost* client, ENetEvent* event, enet_uint32 timeoutMs);
 int gracefullyDisconnectEnetPeer(ENetHost* host, ENetPeer* peer, enet_uint32 lingerTimeoutMs);
 int extractVersionQuadFromString(const char* string, int* quad);
+bool isReferenceFrameInvalidationSupportedByDecoder(void);
 bool isReferenceFrameInvalidationEnabled(void);
 void* extendBuffer(void* ptr, size_t newSize);
 

src/Misc.c

@@ -119,18 +119,18 @@ void* extendBuffer(void* ptr, size_t newSize) {
     return newBuf;
 }
 
-bool isReferenceFrameInvalidationEnabled(void) {
+bool isReferenceFrameInvalidationSupportedByDecoder(void) {
     LC_ASSERT(NegotiatedVideoFormat != 0);
 
-    // Even if the client wants it, we can't enable it without server support.
-    if (!ReferenceFrameInvalidationSupported) {
-        return false;
-    }
-
     return ((NegotiatedVideoFormat & VIDEO_FORMAT_MASK_H264) && (VideoCallbacks.capabilities & CAPABILITY_REFERENCE_FRAME_INVALIDATION_AVC)) ||
            ((NegotiatedVideoFormat & VIDEO_FORMAT_MASK_H265) && (VideoCallbacks.capabilities & CAPABILITY_REFERENCE_FRAME_INVALIDATION_HEVC));
 }
 
+bool isReferenceFrameInvalidationEnabled(void) {
+    // RFI must be supported by the server and the client decoder to be used
+    return ReferenceFrameInvalidationSupported && isReferenceFrameInvalidationSupportedByDecoder();
+}
+
 void LiInitializeStreamConfiguration(PSTREAM_CONFIGURATION streamConfig) {
     memset(streamConfig, 0, sizeof(*streamConfig));
 }

src/SdpGenerator.c

@@ -386,7 +386,11 @@ static PSDP_OPTION getAttributesList(char*urlSafeAddr) {
         }
 
         if (AppVersionQuad[0] >= 7) {
-            if (isReferenceFrameInvalidationEnabled()) {
+            // If the decoder supports reference frame invalidation, that indicates it also supports
+            // the maximum number of reference frames allowed by the codec. Even if we can't use RFI
+            // due to lack of host support, we can still allow the host to pick a number of reference
+            // frames greater than 1 to improve encoding efficiency.
+            if (isReferenceFrameInvalidationSupportedByDecoder()) {
                 err |= addAttributeString(&optionHead, "x-nv-video[0].maxNumReferenceFrames", "0");
             }
             else {