feat(fps): support x-nv-video[0].clientRefreshRateX100 for requesting fractional NTSC framerates (#4019)

src/nvenc/nvenc_base.cpp

@@ -225,6 +225,11 @@ namespace nvenc {
     init_params.darHeight = encoder_params.height;
     init_params.frameRateNum = client_config.framerate;
     init_params.frameRateDen = 1;
+    if (client_config.framerateX100 > 0) {
+      AVRational fps = video::framerateX100_to_rational(client_config.framerateX100);
+      init_params.frameRateNum = fps.num;
+      init_params.frameRateDen = fps.den;
+    }
 
     NV_ENC_PRESET_CONFIG preset_config = {min_struct_version(NV_ENC_PRESET_CONFIG_VER), {min_struct_version(NV_ENC_CONFIG_VER, 7, 8)}};
     if (nvenc_failed(nvenc->nvEncGetEncodePresetConfigEx(encoder, init_params.encodeGUID, init_params.presetGUID, init_params.tuningInfo, &preset_config))) {

src/platform/windows/display.h

@@ -173,6 +173,7 @@ namespace platf::dxgi {
     int height_before_rotation;
 
     int client_frame_rate;
+    DXGI_RATIONAL client_frame_rate_strict;
 
     DXGI_FORMAT capture_format;
     D3D_FEATURE_LEVEL feature_level;

src/platform/windows/display_base.cpp

@@ -121,7 +121,13 @@ namespace platf::dxgi {
     display->display_refresh_rate = dup_desc.ModeDesc.RefreshRate;
     double display_refresh_rate_decimal = (double) display->display_refresh_rate.Numerator / display->display_refresh_rate.Denominator;
     BOOST_LOG(info) << "Display refresh rate [" << display_refresh_rate_decimal << "Hz]";
-    BOOST_LOG(info) << "Requested frame rate [" << display->client_frame_rate << "fps]";
+    if (display->client_frame_rate_strict.Numerator > 0) {
+      int num = display->client_frame_rate_strict.Numerator;
+      int den = display->client_frame_rate_strict.Denominator;
+      BOOST_LOG(info) << "Requested frame rate [" << num << "/" << den << " exactly " << av_q2d(AVRational {num, den}) << " fps]";
+    } else {
+      BOOST_LOG(info) << "Requested frame rate [" << display->client_frame_rate << "fps]";
+    }
     display->display_refresh_rate_rounded = lround(display_refresh_rate_decimal);
     return 0;
   }
@@ -196,6 +202,10 @@ namespace platf::dxgi {
 
   capture_e display_base_t::capture(const push_captured_image_cb_t &push_captured_image_cb, const pull_free_image_cb_t &pull_free_image_cb, bool *cursor) {
     auto adjust_client_frame_rate = [&]() -> DXGI_RATIONAL {
+      // Use exactly the requested rate if the client sent an X100 value
+      if (client_frame_rate_strict.Numerator > 0) {
+        return client_frame_rate_strict;
+      }
       // Adjust capture frame interval when display refresh rate is not integral but very close to requested fps.
       if (display_refresh_rate.Denominator > 1) {
         DXGI_RATIONAL candidate = display_refresh_rate;
@@ -705,6 +715,12 @@ namespace platf::dxgi {
     }
 
     client_frame_rate = config.framerate;
+    client_frame_rate_strict = {0, 0};
+    if (config.framerateX100 > 0) {
+      AVRational fps = ::video::framerateX100_to_rational(config.framerateX100);
+      client_frame_rate_strict = DXGI_RATIONAL {static_cast<UINT>(fps.num), static_cast<UINT>(fps.den)};
+    }
+
     dxgi::output6_t output6 {};
     status = output->QueryInterface(IID_IDXGIOutput6, (void **) &output6);
     if (SUCCEEDED(status)) {

src/rtsp.cpp

@@ -952,6 +952,7 @@ namespace rtsp_stream {
     args.try_emplace("x-ss-general.encryptionEnabled"sv, "0"sv);
     args.try_emplace("x-ss-video[0].chromaSamplingType"sv, "0"sv);
     args.try_emplace("x-ss-video[0].intraRefresh"sv, "0"sv);
+    args.try_emplace("x-nv-video[0].clientRefreshRateX100"sv, "0"sv);
 
     stream::config_t config;
 
@@ -981,6 +982,7 @@ namespace rtsp_stream {
       config.monitor.height = util::from_view(args.at("x-nv-video[0].clientViewportHt"sv));
       config.monitor.width = util::from_view(args.at("x-nv-video[0].clientViewportWd"sv));
       config.monitor.framerate = util::from_view(args.at("x-nv-video[0].maxFPS"sv));
+      config.monitor.framerateX100 = util::from_view(args.at("x-nv-video[0].clientRefreshRateX100"sv));
       config.monitor.bitrate = util::from_view(args.at("x-nv-vqos[0].bw.maximumBitrateKbps"sv));
       config.monitor.slicesPerFrame = util::from_view(args.at("x-nv-video[0].videoEncoderSlicesPerFrame"sv));
       config.monitor.numRefFrames = util::from_view(args.at("x-nv-video[0].maxNumReferenceFrames"sv));

src/video.cpp

@@ -1532,6 +1532,11 @@ namespace video {
       ctx->height = config.height;
       ctx->time_base = AVRational {1, config.framerate};
       ctx->framerate = AVRational {config.framerate, 1};
+      if (config.framerateX100 > 0) {
+        AVRational fps = video::framerateX100_to_rational(config.framerateX100);
+        ctx->framerate = fps;
+        ctx->time_base = AVRational {fps.den, fps.num};
+      }
 
       switch (config.videoFormat) {
         case 0:

src/video.h

@@ -24,6 +24,7 @@ namespace video {
     int width;  // Video width in pixels
     int height;  // Video height in pixels
     int framerate;  // Requested framerate, used in individual frame bitrate budget calculation
+    int framerateX100;  // Optional field for streaming at NTSC or similar rates e.g. 59.94 = 5994
     int bitrate;  // Video bitrate in kilobits (1000 bits) for requested framerate
     int slicesPerFrame;  // Number of slices per frame
     int numRefFrames;  // Max number of reference frames
@@ -352,4 +353,25 @@ namespace video {
    * @warning This is only safe to call when there is no client actively streaming.
    */
   int probe_encoders();
+
+  // Several NTSC standard refresh rates are hardcoded here, because their
+  // true rate requires a denominator of 1001. ffmpeg's av_d2q() would assume it could
+  // reduce 29.97 to 2997/100 but this would be slightly wrong. We also include
+  // support for 23.976 film in case someone wants to stream a film at the perfect
+  // framerate.
+  inline AVRational framerateX100_to_rational(const int framerateX100) {
+    if (framerateX100 % 2997 == 0) {
+      // Multiples of NTSC 29.97 e.g. 59.94, 119.88
+      return AVRational {(framerateX100 / 2997) * 30000, 1001};
+    }
+    switch (framerateX100) {
+      case 2397:  // the other weird NTSC framerate, assume these want 23.976 film
+      case 2398:
+        return AVRational {24000, 1001};
+      default:
+        // any other fractional rate can be reduced by ffmpeg. Max is set to 1 << 26 based on docs:
+        // "rational numbers with |num| <= 1<<26 && |den| <= 1<<26 can be recovered exactly from their double representation"
+        return av_d2q((double) framerateX100 / 100.0f, 1 << 26);
+    }
+  }
 }  // namespace video