refactor(host): hoist the direct-NVENC init-params authoring into nvenc_core

Both backends' build_init_params authored an identical NV_ENC_INITIALIZE_PARAMS
(P1/ULL preset, PTD, session dimensions/rate, split-encode mode) — the only
difference was the Windows-only enableEncodeAsync flag (Linux is sync-only).
Hoist it to nvenc_core::build_init_params(codec_guid, w, h, fps, cfg, split_mode,
enable_async); Linux's two call sites pass enable_async=false (the field stays 0
as before), Windows passes its session_async through. Keeps open and in-place
reconfigure presenting the SAME init params, now guaranteed identical across
platforms too.

Verified on BOTH platforms: Linux clippy 0/0 (nvenc,vulkan-encode,pyrowave, RTX
5070 Ti) and Windows clippy 0/0 (nvenc,amf-qsv, RTX 4090 / .173).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/punktfunk-host/src/encode/linux/nvenc_cuda.rs

@@ -32,7 +32,7 @@
 #![deny(clippy::undocumented_unsafe_blocks)]
 
 use super::nvenc_core::{
-    apply_low_latency_config, codec_guid, LowLatencyConfig, NvStatusExt, RFI_DPB,
+    apply_low_latency_config, build_init_params, codec_guid, LowLatencyConfig, NvStatusExt, RFI_DPB,
 };
 use super::nvenc_status;
 use super::{ChromaFormat, Codec, EncodedFrame, Encoder, EncoderCaps};
@@ -599,34 +599,6 @@ impl NvencCudaEncoder {
         Ok(cfg)
     }
 
-    /// Author the `NV_ENC_INITIALIZE_PARAMS` pointing at `cfg`. Shared by [`try_open_session`]
-    /// and [`Encoder::reconfigure_bitrate`] — a reconfigure must present the SAME init params as
-    /// the open. The returned struct borrows `cfg` raw; the caller keeps `cfg` alive across the
-    /// NVENC call it feeds this into.
-    fn build_init_params(
-        &self,
-        cfg: &mut nv::NV_ENC_CONFIG,
-        split_mode: u32,
-    ) -> nv::NV_ENC_INITIALIZE_PARAMS {
-        let mut init = nv::NV_ENC_INITIALIZE_PARAMS {
-            version: nv::NV_ENC_INITIALIZE_PARAMS_VER,
-            encodeGUID: self.codec_guid,
-            presetGUID: nv::NV_ENC_PRESET_P1_GUID,
-            tuningInfo: nv::NV_ENC_TUNING_INFO::NV_ENC_TUNING_INFO_ULTRA_LOW_LATENCY,
-            encodeWidth: self.width,
-            encodeHeight: self.height,
-            darWidth: self.width,
-            darHeight: self.height,
-            frameRateNum: self.fps,
-            frameRateDen: 1,
-            enablePTD: 1,
-            encodeConfig: cfg,
-            ..Default::default()
-        };
-        init.set_splitEncodeMode(split_mode);
-        init
-    }
-
     /// Open + configure + initialize ONE NVENC CUDA session at `bitrate` (bps) and `split_mode`.
     /// Returns the session handle, or destroys it and returns the error.
     unsafe fn try_open_session(&self, bitrate: u64, split_mode: u32) -> Result<*mut c_void> {
@@ -654,7 +626,15 @@ impl NvencCudaEncoder {
                 return Err(e);
             }
         };
-        let mut init = self.build_init_params(&mut cfg, split_mode);
+        let mut init = build_init_params(
+            self.codec_guid,
+            self.width,
+            self.height,
+            self.fps,
+            &mut cfg,
+            split_mode,
+            false,
+        );
 
         match (api().initialize_encoder)(enc, &mut init).nv_ok() {
             Ok(()) => Ok(enc),
@@ -1225,7 +1205,15 @@ impl Encoder for NvencCudaEncoder {
             };
             let mut params = nv::NV_ENC_RECONFIGURE_PARAMS {
                 version: nv::NV_ENC_RECONFIGURE_PARAMS_VER,
-                reInitEncodeParams: self.build_init_params(&mut cfg, self.split_mode),
+                reInitEncodeParams: build_init_params(
+                    self.codec_guid,
+                    self.width,
+                    self.height,
+                    self.fps,
+                    &mut cfg,
+                    self.split_mode,
+                    false,
+                ),
                 ..Default::default()
             };
             // Keep the encoder's RC state and reference chain: no reset, no IDR — the in-flight

crates/punktfunk-host/src/encode/nvenc_core.rs

@@ -68,6 +68,42 @@ pub(super) struct LowLatencyConfig {
     pub rfi_supported: bool,
 }
 
+/// Author the shared `NV_ENC_INITIALIZE_PARAMS` (P1/ULL preset, PTD, the session dimensions/rate)
+/// pointing at `cfg`. `enable_async` drives the Windows two-thread async retrieve — Linux is
+/// sync-only and passes `false`, leaving `enableEncodeAsync` at 0 as before. The returned struct
+/// borrows `cfg` as a raw pointer; the caller must keep `cfg` alive across the NVENC call it feeds
+/// this into. Used at open and at in-place reconfigure, which must present the SAME init params.
+#[allow(clippy::too_many_arguments)]
+pub(super) fn build_init_params(
+    codec_guid: nv::GUID,
+    width: u32,
+    height: u32,
+    fps: u32,
+    cfg: &mut nv::NV_ENC_CONFIG,
+    split_mode: u32,
+    enable_async: bool,
+) -> nv::NV_ENC_INITIALIZE_PARAMS {
+    let mut init = nv::NV_ENC_INITIALIZE_PARAMS {
+        version: nv::NV_ENC_INITIALIZE_PARAMS_VER,
+        encodeGUID: codec_guid,
+        presetGUID: nv::NV_ENC_PRESET_P1_GUID,
+        tuningInfo: nv::NV_ENC_TUNING_INFO::NV_ENC_TUNING_INFO_ULTRA_LOW_LATENCY,
+        encodeWidth: width,
+        encodeHeight: height,
+        darWidth: width,
+        darHeight: height,
+        frameRateNum: fps,
+        frameRateDen: 1,
+        enablePTD: 1,
+        enableEncodeAsync: enable_async as u32,
+        encodeConfig: cfg,
+        ..Default::default()
+    };
+    // splitEncodeMode is a C bitfield — set via the generated accessor, not a struct field.
+    init.set_splitEncodeMode(split_mode);
+    init
+}
+
 /// Author the shared low-latency NVENC config onto a **preset-seeded** `cfg`: CBR + infinite GOP +
 /// P-only + ~1-frame VBV, per-codec tier/level, chroma + bit depth, unconditional colour signaling,
 /// and the RFI DPB. The caller seeds `cfg` from the P1/ULL preset first (that call needs the

crates/punktfunk-host/src/encode/windows/nvenc.rs

@@ -37,7 +37,7 @@
 #![deny(clippy::undocumented_unsafe_blocks)]
 
 use super::nvenc_core::{
-    apply_low_latency_config, codec_guid, LowLatencyConfig, NvStatusExt, RFI_DPB,
+    apply_low_latency_config, build_init_params, codec_guid, LowLatencyConfig, NvStatusExt, RFI_DPB,
 };
 use super::nvenc_status;
 use super::{ChromaFormat, Codec, EncodedFrame, Encoder, EncoderCaps};
@@ -742,39 +742,6 @@ impl NvencD3d11Encoder {
         Ok(cfg)
     }
 
-    /// Author the `NV_ENC_INITIALIZE_PARAMS` pointing at `cfg`. Shared by [`try_open_session`]
-    /// and [`Encoder::reconfigure_bitrate`] — a reconfigure must present the SAME init params as
-    /// the open. The returned struct borrows `cfg` raw; the caller keeps `cfg` alive across the
-    /// NVENC call it feeds this into.
-    fn build_init_params(
-        &self,
-        cfg: &mut nv::NV_ENC_CONFIG,
-        split_mode: u32,
-        enable_async: bool,
-    ) -> nv::NV_ENC_INITIALIZE_PARAMS {
-        let mut init = nv::NV_ENC_INITIALIZE_PARAMS {
-            version: nv::NV_ENC_INITIALIZE_PARAMS_VER,
-            encodeGUID: self.codec_guid,
-            presetGUID: nv::NV_ENC_PRESET_P1_GUID,
-            tuningInfo: nv::NV_ENC_TUNING_INFO::NV_ENC_TUNING_INFO_ULTRA_LOW_LATENCY,
-            encodeWidth: self.width,
-            encodeHeight: self.height,
-            darWidth: self.width,
-            darHeight: self.height,
-            frameRateNum: self.fps,
-            frameRateDen: 1,
-            enablePTD: 1,
-            // Two-thread async retrieve (§5.B): completion events signal the retrieve thread
-            // instead of `lock_bitstream` blocking the submit thread.
-            enableEncodeAsync: enable_async as u32,
-            encodeConfig: cfg,
-            ..Default::default()
-        };
-        // splitEncodeMode is a C bitfield — set via the generated accessor, not a struct field.
-        init.set_splitEncodeMode(split_mode);
-        init
-    }
-
     /// Open + configure + initialize ONE NVENC session at `bitrate` (bps) and `split_mode`. Returns
     /// the session handle, or destroys it and returns the error. NVENC has no re-init after a failed
     /// `initialize_encoder`, so the bitrate-clamp search in `init_session` calls this once per probe.
@@ -809,7 +776,15 @@ impl NvencD3d11Encoder {
                 return Err(e);
             }
         };
-        let mut init = self.build_init_params(&mut cfg, split_mode, enable_async);
+        let mut init = build_init_params(
+            self.codec_guid,
+            self.width,
+            self.height,
+            self.fps,
+            &mut cfg,
+            split_mode,
+            enable_async,
+        );
 
         match (api().initialize_encoder)(enc, &mut init).nv_ok() {
             Ok(()) => Ok(enc),
@@ -1541,7 +1516,11 @@ impl Encoder for NvencD3d11Encoder {
             };
             let mut params = nv::NV_ENC_RECONFIGURE_PARAMS {
                 version: nv::NV_ENC_RECONFIGURE_PARAMS_VER,
-                reInitEncodeParams: self.build_init_params(
+                reInitEncodeParams: build_init_params(
+                    self.codec_guid,
+                    self.width,
+                    self.height,
+                    self.fps,
                     &mut cfg,
                     self.split_mode,
                     self.session_async,