feat(codec): use SVT-AV1 for AV1 encoding on 64-bit targets

Encode AV1 with SVT-AV1 v4.2.0 (rtc + low delay + CBR) instead of libaom
on all 64-bit targets; 32-bit targets keep aom. Decoding is unchanged and
the wire format is still AV1, so old peers are unaffected.

- vcpkg overlay port pinned to v4.2.0: static build, LTO off (mixed
  toolchain safety), MSVC >= 1950 inline workaround, no forced llvm
  binutils
- low delay contract: one packet out per picture in, blocking get_packet
- bitrate and frame rate change on the fly via RATE_CHANGE_EVENT /
  FRAME_RATE_CHANGE_EVENT; VideoQoS pushes its pacing rate through the
  new EncoderApi::set_fps, applied only after a successful send
- fall back to aom for i444 (svt-av1 is 4:2:0 only), for unsupported
  resolutions and on encoder init failure
- test_av1 now gates auto AV1 on the encoder actually used, the cached
  verdict is re-keyed (SVT-Y/SVT-N) so upgrades re-measure
- unit tests: per-frame packet contract, aom cross-decode of the
  bitstream, on-the-fly event acceptance

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012Wf7v1KJM6mbhiYxWSz4PH

res/vcpkg/svt-av1/no-force-llvm.diff

@@ -0,0 +1,13 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index c0c9767..93ec320 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -192,7 +192,7 @@ set(PC_LIBS_PRIVATE)
+ set(PC_REQUIRES_PRIVATE)
+
+ #Clang support, required to build static with LTO
+-if(CMAKE_C_COMPILER_ID MATCHES "Clang" AND UNIX AND NOT APPLE)
++if(FALSE)
+     find_program(LLVM_LD_EXE llvm-ld)
+     find_program(LLVM_AR_EXE llvm-ar)
+     find_program(LLVM_RANLIB_EXE llvm-ranlib)

res/vcpkg/svt-av1/no-inline-yy_unpacklo_epi128.diff

@@ -0,0 +1,19 @@
+diff --git a/Source/Lib/ASM_AVX2/synonyms_avx2.h b/Source/Lib/ASM_AVX2/synonyms_avx2.h
+index f615e2569..9a7667724 100644
+--- a/Source/Lib/ASM_AVX2/synonyms_avx2.h
++++ b/Source/Lib/ASM_AVX2/synonyms_avx2.h
+@@ -75,7 +75,13 @@ static INLINE __m256i yy_loadu2_128(const void *hi, const void *lo) {
+     return yy_set_m128i(mhi, mlo);
+ }
+ 
+-static INLINE __m256i yy_unpacklo_epi128(const __m256i in0, const __m256i in1) {
++#if defined(_MSC_VER) && _MSC_VER >= 1950
++#define MAYBE_INLINE NOINLINE
++#else
++#define MAYBE_INLINE INLINE
++#endif
++
++static MAYBE_INLINE __m256i yy_unpacklo_epi128(const __m256i in0, const __m256i in1) {
+     return _mm256_inserti128_si256(in0, _mm256_castsi256_si128(in1), 1);
+ }
+ 

res/vcpkg/svt-av1/portfile.cmake

@@ -0,0 +1,45 @@
+vcpkg_from_gitlab(
+    GITLAB_URL https://gitlab.com
+    OUT_SOURCE_PATH SOURCE_PATH
+    REPO AOMediaCodec/SVT-AV1
+    REF v${VERSION}
+    SHA512 37df96559af179d28acae10cdff98c94ee2c4ee086b2446ab362b57be9adf566d6f2adc28faa30648798d9bc7d18eaeb2d0665e7292982652496b605342e1c4b
+    PATCHES
+        # upstream forces llvm-ld/llvm-ar/llvm-ranlib for clang static builds on
+        # non-Apple unix, which breaks toolchains without the llvm binutils
+        no-force-llvm.diff
+        # MSVC >= 1950 miscompiles the inlined yy_unpacklo_epi128
+        no-inline-yy_unpacklo_epi128.diff
+)
+
+if(VCPKG_TARGET_ARCHITECTURE MATCHES "^(x86|x64)$")
+    # NASM is required to build the x86/x64 assembly
+    vcpkg_find_acquire_program(NASM)
+    set(SIMD_OPTIONS -DCOMPILE_C_ONLY=OFF "-DCMAKE_ASM_NASM_COMPILER=${NASM}")
+elseif(VCPKG_TARGET_ARCHITECTURE MATCHES "^(arm64|arm64ec)$" AND NOT VCPKG_TARGET_IS_WINDOWS)
+    set(SIMD_OPTIONS -DCOMPILE_C_ONLY=OFF)
+else()
+    set(SIMD_OPTIONS -DCOMPILE_C_ONLY=ON)
+endif()
+
+vcpkg_cmake_configure(
+    SOURCE_PATH "${SOURCE_PATH}"
+    OPTIONS
+        ${SIMD_OPTIONS}
+        -DBUILD_APPS=OFF
+        -DBUILD_TESTING=OFF
+        -DREPRODUCIBLE_BUILDS=ON
+        # SVT-AV1 defaults LTO to ON for gcc>=9/clang>=12, which puts LTO
+        # bitcode into the static archive and breaks linking with a different
+        # compiler version
+        -DSVT_AV1_LTO=OFF
+)
+
+vcpkg_cmake_install()
+vcpkg_cmake_config_fixup(PACKAGE_NAME SVT-AV1 CONFIG_PATH lib/cmake/SVT-AV1)
+vcpkg_copy_pdbs()
+vcpkg_fixup_pkgconfig()
+
+file(REMOVE_RECURSE "${CURRENT_PACKAGES_DIR}/debug/include")
+
+vcpkg_install_copyright(FILE_LIST "${SOURCE_PATH}/LICENSE.md" "${SOURCE_PATH}/PATENTS.md")

res/vcpkg/svt-av1/vcpkg.json

@@ -0,0 +1,19 @@
+{
+  "name": "svt-av1",
+  "version-semver": "4.2.0",
+  "port-version": 0,
+  "description": "Scalable Video Technology AV1 software video encoder library",
+  "homepage": "https://gitlab.com/AOMediaCodec/SVT-AV1",
+  "license": "BSD-3-Clause-Clear",
+  "supports": "!x86 & !arm32 & !uwp",
+  "dependencies": [
+    {
+      "name": "vcpkg-cmake",
+      "host": true
+    },
+    {
+      "name": "vcpkg-cmake-config",
+      "host": true
+    }
+  ]
+}