Switch Linux/Dolphin MP3 decode from minimp3 to libmad

minimp3's sliding-window frame confirmation could spuriously discard real
frames near the tail of a not-yet-full window, losing ~5.5% of a real
VBR file's content even at a tuned 256KB window (~0.3% residual) -
audible as the whole track finishing early with stutters at each drop.

libmad's mad_stream/mad_frame/mad_synth API reports "need more data"
(MAD_ERROR_BUFLEN) and "genuinely bad data" separately rather than
overloading one return value, which was the actual ambiguity minimp3
couldn't resolve. Verified against the same real file with a 32KB window
(vs minimp3's 256KB): frame count and duration match the Xing header
exactly. Confirmed building for Linux, GameCube, and Wii (the latter two
via the project's real devkitPPC/libogc Docker toolchain) - libmad ships
inside libogc itself on Dolphin, no separate fetch needed there.

libmad is GPL-licensed, unlike the rest of this MIT project - a
deliberate tradeoff, noted at each site that pulls it in.

Co-Authored-By: Claude Sonnet 5 <[email protected]>

cmake/modules/Findlibmad.cmake

@@ -0,0 +1,32 @@
+# Copyright (c) 2026 Dominic Masters
+#
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+# NOTE: libmad itself is GPL-licensed (see https://www.underbit.com/products/mad/),
+# not MIT like the rest of this project. Any binary linking it must comply
+# with the GPL - a deliberate tradeoff accepted for MP3 decode correctness
+# (see audiostreammp3decodersw.c's own comment on why minimp3 wasn't enough).
+
+find_path(LIBMAD_INCLUDE_DIR NAMES mad.h)
+mark_as_advanced(LIBMAD_INCLUDE_DIR)
+
+find_library(LIBMAD_LIBRARY NAMES mad)
+mark_as_advanced(LIBMAD_LIBRARY)
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(
+  libmad
+  REQUIRED_VARS
+    LIBMAD_LIBRARY
+    LIBMAD_INCLUDE_DIR
+)
+
+if(libmad_FOUND AND NOT TARGET libmad::mad)
+  add_library(libmad::mad UNKNOWN IMPORTED)
+  set_target_properties(libmad::mad
+    PROPERTIES
+      INTERFACE_INCLUDE_DIRECTORIES ${LIBMAD_INCLUDE_DIR}
+      IMPORTED_LOCATION ${LIBMAD_LIBRARY}
+  )
+endif()

cmake/modules/Findminimp3.cmake

@@ -1,28 +0,0 @@
-# Copyright (c) 2026 Dominic Masters
-#
-# This software is released under the MIT License.
-# https://opensource.org/licenses/MIT
-
-# minimp3 has no tagged releases - pinned to a specific commit instead of a
-# branch for reproducibility.
-include(FetchContent)
-FetchContent_Declare(
-  minimp3
-  GIT_REPOSITORY https://github.com/lieff/minimp3.git
-  GIT_TAG        ea99364f61c14656440e8d77e9c233ccf3124633
-)
-
-FetchContent_MakeAvailable(minimp3)
-
-set(MINIMP3_INCLUDE_DIR "${minimp3_SOURCE_DIR}")
-set(MINIMP3_HEADER "${minimp3_SOURCE_DIR}/minimp3.h")
-
-if(EXISTS "${MINIMP3_HEADER}")
-  add_library(minimp3 INTERFACE)
-  target_include_directories(minimp3 INTERFACE "${MINIMP3_INCLUDE_DIR}")
-  set(minimp3_FOUND TRUE)
-else()
-  set(minimp3_FOUND FALSE)
-endif()
-
-mark_as_advanced(MINIMP3_INCLUDE_DIR MINIMP3_HEADER)

cmake/targets/dolphin.cmake

@@ -62,6 +62,7 @@ target_link_libraries(${DUSK_LIBRARY_TARGET_NAME} PRIVATE
   z
   lzma
   ansnd
+  mad
 )
 
 if(DUSK_DOLPHIN_BUILD_TYPE STREQUAL "ISO")