fix(stream): handle frame loss before FEC telemetry

Signed-off-by: leandredesmaretz <leandre@eshot.io>

Author: leandredesmaretz

docs/configuration.md

@@ -1405,10 +1405,10 @@ editing the `conf` file in a text editor. Use the examples as reference.
         <td colspan="2">
             Allow supported Moonlight sessions to reduce the video bitrate during sustained network loss. Runtime
             bitrate changes are currently supported by the Windows native NVENC backend. Recovery is gradual and
-            requires both a quiet period without new loss pressure and a fresh, healthy ENet RTT sample from Moonlight's
-            reliable control ping; the absence of FEC reports alone never permits an increase. The controller never
-            exceeds the bitrate requested by Moonlight or the configured `max_bitrate` ceiling. Unsupported clients and
-            encoders continue to use their fixed effective bitrate.
+            requires both a quiet period without new loss pressure and a fresh, healthy ENet RTT sample produced by a
+            reliable acknowledgement from Moonlight; the absence of FEC reports alone never permits an increase. The
+            controller never exceeds the bitrate requested by Moonlight or the configured `max_bitrate` ceiling.
+            Unsupported clients and encoders continue to use their fixed effective bitrate.
         </td>
     </tr>
     <tr>

src/adaptive_bitrate.cpp

@@ -148,7 +148,7 @@ namespace stream::adaptive_bitrate {
 
     if (snapshot.fec_reports != 0) {
       telemetry_seen_ = true;
-    } else if (!telemetry_seen_) {
+    } else if (!telemetry_seen_ && snapshot.frame_loss_requests == 0) {
       return;
     }
 

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

@@ -113,7 +113,7 @@
     "adapter_name_desc_windows": "Manually specify a GPU to use for capture. If unset, the GPU is chosen automatically. We strongly recommend leaving this field blank to use automatic GPU selection! Note: This GPU must have a display connected and powered on. The appropriate values can be found using the following command:",
     "adapter_name_placeholder_windows": "Radeon RX 580 Series",
     "adaptive_bitrate": "Adaptive Bitrate",
-    "adaptive_bitrate_desc": "Allow supported Moonlight sessions using the Windows native NVENC encoder to reduce bitrate during sustained network loss. Recovery is gradual and requires a fresh, healthy ENet RTT sample from Moonlight's reliable control ping.",
+    "adaptive_bitrate_desc": "Allow supported Moonlight sessions using the Windows native NVENC encoder to reduce bitrate during sustained network loss. Recovery is gradual and requires a fresh, healthy ENet RTT sample produced by a reliable acknowledgement from Moonlight.",
     "add": "Add",
     "address_family": "Address Family",
     "address_family_both": "IPv4+IPv6",

tests/unit/test_adaptive_bitrate.cpp

@@ -291,15 +291,14 @@ TEST(AdaptiveBitrateControllerTest, DoesNotDecreaseForFecRecoveryWithoutLatencyC
   EXPECT_EQ(controller.target_kbps(), 25'000U);
 }
 
-TEST(AdaptiveBitrateControllerTest, RepeatedFrameLossRequestsUseSevereDecreasePath) {
+TEST(AdaptiveBitrateControllerTest, RepeatedFrameLossRequestsBeforeFecTelemetryUseSevereDecreasePath) {
   const adaptive::time_point_t start {};
   adaptive::controller_t controller;
   activate(controller, start);
 
-  controller.observe(make_snapshot(1, 10'000, 0, 0), start + 100ms);
-  auto first_loss_request = make_snapshot(2, 0, 0, 0, 20, 2, 1);
+  auto first_loss_request = make_snapshot(1, 0, 0, 0, 20, 2, 1);
   first_loss_request.fec_reports = 0;
-  auto second_loss_request = make_snapshot(3, 0, 0, 0, 20, 2, 1);
+  auto second_loss_request = make_snapshot(2, 0, 0, 0, 20, 2, 1);
   second_loss_request.fec_reports = 0;
   controller.observe(first_loss_request, start + 500ms);
   controller.observe(second_loss_request, start + 1s);