feat(vaapi): add option to enable strict enforcement of frame size

docs/configuration.md

@@ -2303,6 +2303,33 @@ editing the `conf` file in a text editor. Use the examples as reference.
     </tr>
 </table>
 
+## VA-API Encoder
+
+### vaapi_strict_rc_buffer
+
+<table>
+    <tr>
+        <td>Description</td>
+        <td colspan="2">
+            Enabling this option can avoid dropped frames over the network during scene changes, but video quality may
+            be reduced during motion.
+            @note{This option only applies for H.264 and HEVC when using VA-API [encoder](#encoder) on AMD GPUs.}
+        </td>
+    </tr>
+    <tr>
+        <td>Default</td>
+        <td colspan="2">@code{}
+            disabled
+            @endcode</td>
+    </tr>
+    <tr>
+        <td>Example</td>
+        <td colspan="2">@code{}
+            vaapi_strict_rc_buffer = enabled
+            @endcode</td>
+    </tr>
+</table>
+
 ## Software Encoder
 
 ### sw_preset

src/config.cpp

@@ -377,6 +377,10 @@ namespace config {
       -1,
     },  // vt
 
+    {
+      false,  // strict_rc_buffer
+    },  // vaapi
+
     {},  // capture
     {},  // encoder
     {},  // adapter_name
@@ -1014,6 +1018,8 @@ namespace config {
     int_f(vars, "vt_software", video.vt.vt_require_sw, vt::force_software_from_view);
     int_f(vars, "vt_realtime", video.vt.vt_realtime, vt::rt_from_view);
 
+    bool_f(vars, "vaapi_strict_rc_buffer", video.vaapi.strict_rc_buffer);
+
     string_f(vars, "capture", video.capture);
     string_f(vars, "encoder", video.encoder);
     string_f(vars, "adapter_name", video.adapter_name);

src/config.h

@@ -71,6 +71,10 @@ namespace config {
       int vt_coder;
     } vt;
 
+    struct {
+      bool strict_rc_buffer;
+    } vaapi;
+
     std::string capture;
     std::string encoder;
     std::string adapter_name;

src/platform/common.h

@@ -418,7 +418,7 @@ namespace platf {
      * @note Implementations may set or modify codec options prior to codec initialization.
      */
     virtual void
-    init_codec_options(AVCodecContext *ctx, AVDictionary *options) {};
+    init_codec_options(AVCodecContext *ctx, AVDictionary **options) {};
 
     /**
      * @brief Prepare to derive a context.

src/platform/linux/vaapi.cpp

@@ -130,11 +130,24 @@ namespace va {
     }
 
     void
-    init_codec_options(AVCodecContext *ctx, AVDictionary *options) override {
-      // Don't set the RC buffer size when using H.264 on Intel GPUs. It causes
-      // major encoding quality degradation.
+    init_codec_options(AVCodecContext *ctx, AVDictionary **options) override {
       auto vendor = vaQueryVendorString(va_display);
-      if (ctx->codec_id != AV_CODEC_ID_H264 || (vendor && !strstr(vendor, "Intel"))) {
+
+      // Use VBR with a single frame VBV when the user forces it and for known good cases:
+      // - Intel GPUs
+      // - AV1
+      //
+      // VBR ensures the bitstream isn't full of filler data for bitrate undershoots and
+      // single frame VBV ensures that we don't have large bitrate overshoots (at least
+      // as much as they can be avoided without pre-analysis).
+      //
+      // When we have to resort to the default 1 second VBV for encoding quality reasons,
+      // we stick to CBR in order to avoid encoding huge frames after bitrate undershoots
+      // leave headroom available in the RC window.
+      if (config::video.vaapi.strict_rc_buffer ||
+          (vendor && strstr(vendor, "Intel")) ||
+          ctx->codec_id == AV_CODEC_ID_AV1) {
+        av_dict_set(options, "rc_mode", "VBR", 0);
         ctx->rc_buffer_size = ctx->bit_rate * ctx->framerate.den / ctx->framerate.num;
       }
     }

src/video.cpp

@@ -1696,7 +1696,7 @@ namespace video {
       }
 
       // Allow the encoding device a final opportunity to set/unset or override any options
-      encode_device->init_codec_options(ctx.get(), options);
+      encode_device->init_codec_options(ctx.get(), &options);
 
       if (auto status = avcodec_open2(ctx.get(), codec, &options)) {
         char err_str[AV_ERROR_MAX_STRING_SIZE] { 0 };

src_assets/common/assets/web/config.html

@@ -257,6 +257,13 @@ <h1 class="my-4">{{ $t('config.configuration') }}</h1>
               "vt_realtime": "enabled",
             },
           },
+          {
+            id: "vaapi",
+            name: "VA-API Encoder",
+            options: {
+              "vaapi_strict_rc_buffer": "disabled",
+            },
+          },
           {
             id: "sw",
             name: "Software Encoder",
@@ -283,7 +290,7 @@ <h1 class="my-4">{{ $t('config.configuration') }}</h1>
           var app = document.getElementById("app");
           if (this.platform === "windows") {
             this.tabs = this.tabs.filter((el) => {
-              return el.id !== "vt";
+              return el.id !== "vt" && el.id !== "vaapi";
             });
           }
           if (this.platform === "linux") {
@@ -293,7 +300,7 @@ <h1 class="my-4">{{ $t('config.configuration') }}</h1>
           }
           if (this.platform === "macos") {
             this.tabs = this.tabs.filter((el) => {
-              return el.id !== "amd" && el.id !== "nv" && el.id !== "qsv";
+              return el.id !== "amd" && el.id !== "nv" && el.id !== "qsv" && el.id !== "vaapi";
             });
           }
 

src_assets/common/assets/web/configs/tabs/ContainerEncoders.vue

@@ -5,6 +5,7 @@ import IntelQuickSyncEncoder from './encoders/IntelQuickSyncEncoder.vue'
 import AmdAmfEncoder from './encoders/AmdAmfEncoder.vue'
 import VideotoolboxEncoder from './encoders/VideotoolboxEncoder.vue'
 import SoftwareEncoder from './encoders/SoftwareEncoder.vue'
+import VAAPIEncoder from './encoders/VAAPIEncoder.vue'
 
 const props = defineProps([
   'platform',
@@ -45,6 +46,13 @@ const config = ref(props.config)
       :config="config"
   />
 
+  <!-- VAAPI Encoder Tab -->
+  <VAAPIEncoder
+      v-if="currentTab === 'vaapi'"
+      :platform="platform"
+      :config="config"
+  />
+
   <!-- Software Encoder Tab -->
   <SoftwareEncoder
       v-if="currentTab === 'sw'"

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

@@ -0,0 +1,28 @@
+<script setup>
+import { ref } from 'vue'
+
+const props = defineProps([
+  'platform',
+  'config',
+])
+
+const config = ref(props.config)
+</script>
+
+<template>
+  <div id="vaapi-encoder" class="config-page">
+    <!-- Strict RC Buffer -->
+    <div class="mb-3">
+      <label for="vaapi_strict_rc_buffer" class="form-label">{{ $t('config.vaapi_strict_rc_buffer') }}</label>
+      <select id="vaapi_strict_rc_buffer" class="form-select" v-model="config.vaapi_strict_rc_buffer">
+        <option value="enabled">{{ $t('_common.enabled') }}</option>
+        <option value="disabled">{{ $t('_common.disabled') }}</option>
+      </select>
+      <div class="form-text">{{ $t('config.vaapi_strict_rc_buffer_desc') }}</div>
+    </div>
+  </div>
+</template>
+
+<style scoped>
+
+</style>

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

@@ -310,6 +310,8 @@
     "touchpad_as_ds4_desc": "If disabled, touchpad presence will not be taken into account during gamepad type selection.",
     "upnp": "UPnP",
     "upnp_desc": "Automatically configure port forwarding for streaming over the Internet",
+    "vaapi_strict_rc_buffer": "Strictly enforce frame bitrate limits for H.264/HEVC on AMD GPUs",
+    "vaapi_strict_rc_buffer_desc": "Enabling this option can avoid dropped frames over the network during scene changes, but video quality may be reduced during motion.",
     "virtual_sink": "Virtual Sink",
     "virtual_sink_desc": "Manually specify a virtual audio device to use. If unset, the device is chosen automatically. We strongly recommend leaving this field blank to use automatic device selection!",
     "virtual_sink_placeholder": "Steam Streaming Speakers",