audio: ffmpeg_dec: add MP3 decoder

Add CONFIG_FFMPEG_DEC_MP3: enables the libavcodec mp3 decoder and mpegaudio
parser in the cross-build, the FFMPEG_DEC_CODEC_MP3 codec id mapping, and the
float math layer (the mp3 decoder uses it). Verified building for ace30 (ptl)
with decoders [flac,mp3].

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lrgirdwo

src/audio/ffmpeg_dec/Kconfig

@@ -45,6 +45,12 @@ config FFMPEG_DEC_OPUS
 	  Opus (SILK+CELT) decoder. Pulls in the single-precision float math
 	  layer. Enables --enable-decoder=opus in the libavcodec build.
 
+config FFMPEG_DEC_MP3
+	bool "MP3 decoder"
+	help
+	  MPEG-1/2 Layer III decoder. Enables --enable-decoder=mp3 and the
+	  mpegaudio parser in the libavcodec build. Uses the float math layer.
+
 comment "FFmpeg audio filters (libavfilter; need the avfilter-graph backend to run)"
 
 config FFMPEG_FILTER_AFFTDN
@@ -75,7 +81,7 @@ config FFMPEG_BUILD_AVFILTER
 # built. Gates compilation of the fast single-precision libm (fastmathf.c).
 config FFMPEG_DEC_FLOAT_MATH
 	bool
-	default y if FFMPEG_DEC_AAC || FFMPEG_DEC_OPUS || FFMPEG_FILTER_AFFTDN
+	default y if FFMPEG_DEC_AAC || FFMPEG_DEC_OPUS || FFMPEG_DEC_MP3 || FFMPEG_FILTER_AFFTDN
 
 config FFMPEG_DEC_COLD_SPLIT
 	bool "Place cold FFmpeg code (av_cold init/setup) in DRAM [EXPERIMENTAL]"

src/audio/ffmpeg_dec/ffmpeg.cmake

@@ -38,6 +38,10 @@ if(CONFIG_FFMPEG_DEC_OPUS)
 	list(APPEND _ff_decoders opus)
 	list(APPEND _ff_parsers  opus)
 endif()
+if(CONFIG_FFMPEG_DEC_MP3)
+	list(APPEND _ff_decoders mp3)
+	list(APPEND _ff_parsers  mpegaudio)
+endif()
 if(NOT _ff_decoders)
 	message(FATAL_ERROR "ffmpeg_dec: no decoder selected (Kconfig FFMPEG_DEC_*)")
 endif()

src/audio/ffmpeg_dec/ffmpeg_dec-ffmpeg.c

@@ -100,6 +100,10 @@ static enum AVCodecID ffmpeg_dec_av_codec_id(enum ffmpeg_dec_codec codec)
 #if defined(CONFIG_FFMPEG_DEC_OPUS)
 	case FFMPEG_DEC_CODEC_OPUS:
 		return AV_CODEC_ID_OPUS;
+#endif
+#if defined(CONFIG_FFMPEG_DEC_MP3)
+	case FFMPEG_DEC_CODEC_MP3:
+		return AV_CODEC_ID_MP3;
 #endif
 	default:
 		return AV_CODEC_ID_NONE;

src/audio/ffmpeg_dec/ffmpeg_dec.h

@@ -32,6 +32,7 @@ enum ffmpeg_dec_codec {
 	FFMPEG_DEC_CODEC_FLAC,
 	FFMPEG_DEC_CODEC_AAC,
 	FFMPEG_DEC_CODEC_OPUS,
+	FFMPEG_DEC_CODEC_MP3,
 };
 
 /* Default codec for a new instance, picked from the Kconfig selection until the
@@ -43,6 +44,8 @@ enum ffmpeg_dec_codec {
 #define FFMPEG_DEC_DEFAULT_CODEC	FFMPEG_DEC_CODEC_AAC
 #elif defined(CONFIG_FFMPEG_DEC_OPUS)
 #define FFMPEG_DEC_DEFAULT_CODEC	FFMPEG_DEC_CODEC_OPUS
+#elif defined(CONFIG_FFMPEG_DEC_MP3)
+#define FFMPEG_DEC_DEFAULT_CODEC	FFMPEG_DEC_CODEC_MP3
 #else
 #define FFMPEG_DEC_DEFAULT_CODEC	FFMPEG_DEC_CODEC_NONE
 #endif