jni: add libmpg123

app/src/main/cpp/CMakeLists.txt

@@ -29,6 +29,8 @@ add_library(${CMAKE_PROJECT_NAME} SHARED
     # List C/C++ source files with relative paths to this CMakeLists.txt.
     lockstep.cpp
     PlaybackEngine.cpp
+    mp3file.cpp
+    jni_bridge.cpp
 )
 
 find_package (oboe REQUIRED CONFIG)
@@ -36,13 +38,25 @@ find_package (oboe REQUIRED CONFIG)
 add_library(ndk-logger SHARED logging.cpp logging_jni.cpp)
 target_link_libraries(ndk-logger log)
 
+# Add pre-built libmpg123 library
+add_library(mpg123 SHARED IMPORTED)
+set(mpg123_DIR ${CMAKE_SOURCE_DIR}/../lib/mpg123)
+set_target_properties(mpg123 PROPERTIES IMPORTED_LOCATION
+        ${mpg123_DIR}/lib/${ANDROID_ABI}/libmpg123.so)
+include_directories(${mpg123_DIR}/lib/${ANDROID_ABI}/include)
+
 # Specifies libraries CMake should link to your target library. You
 # can link libraries from various origins, such as libraries defined in this
 # build script, prebuilt third-party libraries, or Android system libraries.
 target_link_libraries(${CMAKE_PROJECT_NAME}
     # List libraries link to the target library
     oboe::oboe
+    mpg123
     android
     log
     ndk-logger
 )
+
+# Enable optimization flags: if having problems with source level debugging,
+# disable -Ofast ( and debug ), re-enable after done debugging.
+target_compile_options(${CMAKE_PROJECT_NAME} PRIVATE -Wall -Werror "$<$<CONFIG:RELEASE>:-Ofast>")

app/src/main/cpp/jni_bridge.cpp

@@ -0,0 +1,16 @@
+//
+// Created by david on 02.03.2026.
+//
+
+#include <jni.h>
+#include "mpg123.h"
+
+extern "C" {
+
+JNIEXPORT jint JNICALL
+Java_at_lockstep_pb_PlaybackEngine_native_1mpg123_1init
+        (JNIEnv *env, jclass) {
+    return mpg123_init();
+}
+
+}

app/src/main/cpp/mp3file.cpp

@@ -0,0 +1,93 @@
+//
+// Created by david on 17.05.20.
+//
+
+#define LOG_TAG "mp3file"
+
+#include "mp3file.h"
+#include <string.h>
+#include <cstdlib>
+#include "logging.h"
+
+MP3File* mp3file_init(mpg123_handle *handle) {
+    MP3File* mp3file = (MP3File *) malloc(sizeof(MP3File));
+    if(mp3file == NULL) return NULL;
+    memset(mp3file, 0, sizeof(MP3File));
+    mp3file->handle = handle;
+    return mp3file;
+}
+
+void mp3file_delete(MP3File *mp3file) {
+    if(mp3file == NULL) return;
+    mpg123_close(mp3file->handle);
+    mpg123_delete(mp3file->handle);
+    if(mp3file->buffer) {
+        free(mp3file->buffer);
+        mp3file->buffer = 0;
+    }
+    free(mp3file);
+}
+
+MP3File* mp3file_open(const char *filename, int forceEncoding) {
+    const char *errorText = "";
+#define handleError(text) \
+    do { \
+        errorText = text; \
+        goto on_error; \
+    } while(0)
+
+    int err = MPG123_OK;
+    mpg123_handle *mh = mpg123_new(NULL, &err);
+    if(err != MPG123_OK || mh == NULL) {
+        LOGE("mpg123_new() failed: %s", mpg123_plain_strerror(err));
+        return NULL;
+    }
+
+    MP3File* mp3 = mp3file_init(mh);
+    if(mp3 == NULL) handleError("malloc() failed");
+    err = mpg123_open(mh, filename);
+    if(err != MPG123_OK) handleError("mpg123_open()");
+
+    int encoding;
+    err = mpg123_getformat(mh, &mp3->rate, &mp3->channels, &encoding);
+    if(err != MPG123_OK) handleError("mpg123_getformat()");
+    if(encoding != MPG123_ENC_SIGNED_16) handleError("unknown file encoding");
+
+    if(forceEncoding != 0) {
+        encoding = forceEncoding;
+    }
+
+    // Ensure that this output format will not change
+    // (it could, when we allow it).
+    mpg123_format_none(mh);
+    err = mpg123_format(mh, mp3->rate, mp3->channels, encoding);
+    if(err != MPG123_OK) handleError("could not set mpg123_format()");
+
+    mp3->buffer_size = mpg123_outblock(mh);
+    mp3->buffer = (unsigned char*) malloc(mp3->buffer_size);
+    if(mp3->buffer == NULL) handleError("malloc() failed");
+
+    mp3->num_samples = mpg123_length(mh);
+    mp3->samples_per_frame = mpg123_spf(mh);
+    mp3->secs_per_frame = mpg123_tpf(mh);
+
+    if (mp3->num_samples == MPG123_ERR || mp3->samples_per_frame < 0)
+        mp3->num_frames = 0;
+    else
+        mp3->num_frames = mp3->num_samples / mp3->samples_per_frame;
+
+    if (mp3->num_samples == MPG123_ERR || mp3->samples_per_frame < 0 || mp3->secs_per_frame < 0)
+        mp3->duration = 0;
+    else
+        mp3->duration = mp3->num_samples / mp3->samples_per_frame * mp3->secs_per_frame;
+
+    LOGV("channels: %d rate: %ld num_samples: %ld", mp3->channels, mp3->rate, mp3->num_samples);
+    return mp3;
+
+on_error:
+    LOGE("%s, err = %s", errorText, mpg123_plain_strerror(err));
+    mp3file_delete(mp3);
+    return NULL;
+
+#undef handleError
+}

app/src/main/cpp/mp3file.h

@@ -0,0 +1,30 @@
+//
+// Created by david on 17.05.20.
+//
+
+#ifndef SAMPLES_MP3FILE_H
+#define SAMPLES_MP3FILE_H
+
+#include "mpg123.h"
+
+struct MP3File
+{
+    mpg123_handle* handle;
+    int channels;
+    long rate;
+    long num_samples;
+    int samples_per_frame;
+    double secs_per_frame;
+    long num_frames;
+    double duration;
+    size_t buffer_size;
+    unsigned char* buffer;
+    size_t leftSamples;
+    size_t offset;
+};
+
+MP3File* mp3file_init(mpg123_handle *handle);
+void mp3file_delete(MP3File *mp3file);
+MP3File* mp3file_open(const char *filename, int forceEncoding = 0);
+
+#endif //SAMPLES_MP3FILE_H