feat(win/nvenc): add split-frame encoding option

docs/configuration.md

@@ -1774,6 +1774,46 @@ editing the `conf` file in a text editor. Use the examples as reference.
     </tr>
 </table>
 
+### [nvenc_split_encode](https://localhost:47990/config/#nvenc_split_encode)
+
+<table>
+    <tr>
+        <td>Description</td>
+        <td colspan="2">
+            Split the encoding of each video frame over multiple NVENC hardware units.
+            Significantly reduces encoding latency with a marginal compression efficiency penalty.
+            This option is ignored if your GPU has a singular NVENC unit.
+            @note{This option only applies when using NVENC [encoder](#encoderhttpslocalhost47990configencoder).}
+            @note{Applies to Windows only.}
+        </td>
+    </tr>
+    <tr>
+        <td>Default</td>
+        <td colspan="2">@code{}
+            driver_decides
+            @endcode</td>
+    </tr>
+    <tr>
+        <td>Example</td>
+        <td colspan="2">@code{}
+            nvenc_split_encode = driver_decides
+            @endcode</td>
+    </tr>
+    <tr>
+        <td rowspan="3">Choices</td>
+        <td>disabled</td>
+        <td>Disabled</td>
+    </tr>
+    <tr>
+        <td>driver_decides</td>
+        <td>NVIDIA driver makes the decision whether to enable it</td>
+    </tr>
+    <tr>
+        <td>enabled</td>
+        <td>Enabled</td>
+    </tr>
+</table>
+
 ### [nvenc_latency_over_power](https://localhost:47990/config/#nvenc_latency_over_power)
 
 <table>

src/config.cpp

@@ -56,6 +56,16 @@ namespace config {
       return nvenc::nvenc_two_pass::quarter_resolution;
     }
 
+    nvenc::nvenc_split_frame_encoding
+    split_encode_from_view(const std::string_view &preset) {
+      using enum nvenc::nvenc_split_frame_encoding;
+      if (preset == "disabled") return disabled;
+      if (preset == "driver_decides") return driver_decides;
+      if (preset == "enabled") return force_enabled;
+      BOOST_LOG(warning) << "config: unknown nvenc_split_encode value: " << preset;
+      return driver_decides;
+    }
+
   }  // namespace nv
 
   namespace amd {
@@ -960,6 +970,7 @@ namespace config {
     bool_f(vars, "nvenc_spatial_aq", video.nv.adaptive_quantization);
     generic_f(vars, "nvenc_twopass", video.nv.two_pass, nv::twopass_from_view);
     bool_f(vars, "nvenc_h264_cavlc", video.nv.h264_cavlc);
+    generic_f(vars, "nvenc_split_encode", video.nv.split_frame_encoding, nv::split_encode_from_view);
     bool_f(vars, "nvenc_realtime_hags", video.nv_realtime_hags);
     bool_f(vars, "nvenc_opengl_vulkan_on_dxgi", video.nv_opengl_vulkan_on_dxgi);
     bool_f(vars, "nvenc_latency_over_power", video.nv_sunshine_high_power_mode);

src/nvenc/common_impl/nvenc_base.cpp

@@ -223,6 +223,15 @@ namespace nvenc {
     init_params.frameRateNum = client_config.framerate;
     init_params.frameRateDen = 1;
 
+#if NVENC_INT_VERSION >= 1202
+    {
+      using enum nvenc_split_frame_encoding;
+      init_params.splitEncodeMode = config.split_frame_encoding == disabled      ? NV_ENC_SPLIT_DISABLE_MODE :
+                                    config.split_frame_encoding == force_enabled ? NV_ENC_SPLIT_AUTO_FORCED_MODE :
+                                                                                   NV_ENC_SPLIT_AUTO_MODE;
+    }
+#endif
+
     NV_ENC_PRESET_CONFIG preset_config = {
       .version = NV_ENC_PRESET_CONFIG_VER,
       .presetCfg = { .version = NV_ENC_CONFIG_VER },
@@ -257,8 +266,12 @@ namespace nvenc {
     auto set_h264_hevc_common_format_config = [&](auto &format_config) {
       format_config.repeatSPSPPS = 1;
       format_config.idrPeriod = NVENC_INFINITE_GOPLENGTH;
-      format_config.sliceMode = 3;
-      format_config.sliceModeData = client_config.slicesPerFrame;
+      if (client_config.slicesPerFrame > 1 ||
+          NVENC_INT_VERSION < 1202 ||
+          config.split_frame_encoding == nvenc_split_frame_encoding::disabled) {
+        format_config.sliceMode = 3;
+        format_config.sliceModeData = client_config.slicesPerFrame;
+      }
       if (buffer_is_yuv444()) {
         format_config.chromaFormatIDC = 3;
       }

src/nvenc/nvenc_config.h

@@ -12,6 +12,12 @@ namespace nvenc {
     full_resolution,  ///< Better overall statistics, slower and uses more extra vram
   };
 
+  enum class nvenc_split_frame_encoding {
+    disabled,  ///< Disable
+    driver_decides,  ///< Let driver decide
+    force_enabled,  ///< Force-enable
+  };
+
   /**
    * @brief NVENC encoder configuration.
    */
@@ -48,6 +54,9 @@ namespace nvenc {
 
     // Add filler data to encoded frames to stay at target bitrate, mainly for testing
     bool insert_filler_data = false;
+
+    // Enable split-frame encoding if the gpu has multiple NVENC hardware clusters
+    nvenc_split_frame_encoding split_frame_encoding = nvenc_split_frame_encoding::driver_decides;
   };
 
 }  // namespace nvenc

src_assets/common/assets/web/config.html

@@ -222,6 +222,7 @@ <h1 class="my-4">{{ $t('config.configuration') }}</h1>
               "nvenc_spatial_aq": "disabled",
               "nvenc_vbv_increase": 0,
               "nvenc_realtime_hags": "enabled",
+              "nvenc_split_encode": "driver_decides",
               "nvenc_latency_over_power": "enabled",
               "nvenc_opengl_vulkan_on_dxgi": "enabled",
               "nvenc_h264_cavlc": "disabled",

src_assets/common/assets/web/configs/tabs/encoders/NvidiaNvencEncoder.vue

@@ -85,6 +85,17 @@ const config = ref(props.config)
               </div>
             </div>
 
+            <!-- Split frame encoding -->
+            <div class="mb-3" v-if="platform === 'windows'">
+              <label for="nvenc_split_encode" class="form-label">{{ $t('config.nvenc_split_encode') }}</label>
+              <select id="nvenc_split_encode" class="form-select" v-model="config.nvenc_split_encode">
+                <option value="disabled">{{ $t('_common.disabled') }}</option>
+                <option value="driver_decides">{{ $t('config.nvenc_split_encode_driver_decides_def') }}</option>
+                <option value="enabled">{{ $t('_common.enabled') }}</option>
+              </select>
+              <div class="form-text">{{ $t('config.nvenc_split_encode_desc') }}</div>
+            </div>
+
             <!-- Prefer lower encoding latency over power savings -->
             <div class="mb-3" v-if="platform === 'windows'">
               <label for="nvenc_latency_over_power" class="form-label">{{ $t('config.nvenc_latency_over_power') }}</label>

src_assets/common/assets/web/public/assets/locale/en.json

@@ -239,6 +239,9 @@
     "nvenc_spatial_aq_desc": "Assign higher QP values to flat regions of the video. Recommended to enable when streaming at lower bitrates.",
     "nvenc_spatial_aq_disabled": "Disabled (faster, default)",
     "nvenc_spatial_aq_enabled": "Enabled (slower)",
+    "nvenc_split_encode": "Split frame encoding",
+    "nvenc_split_encode_desc": "Split the encoding of each video frame over multiple NVENC hardware units. Significantly reduces encoding latency with a marginal compression efficiency penalty. This option is ignored if your GPU has a singular NVENC unit.",
+    "nvenc_split_encode_driver_decides_def": "Driver decides (default)",
     "nvenc_twopass": "Two-pass mode",
     "nvenc_twopass_desc": "Adds preliminary encoding pass. This allows to detect more motion vectors, better distribute bitrate across the frame and more strictly adhere to bitrate limits. Disabling it is not recommended since this can lead to occasional bitrate overshoot and subsequent packet loss.",
     "nvenc_twopass_disabled": "Disabled (fastest, not recommended)",