如何将单个Midi通道导出到带有Fluidsynth的WAV？

问题描述

我对音乐技术非常陌生，请多多包涵。

MIDI文件中有16个通道。我正在尝试仅将1个通道从midi文件转换为wav。

这是现在的工作方式：

extern "C" JNIEXPORT void JNICALL Java_com_test_MainActivity_convertMidiToWav(jnienv* env,jobject,jstring jSoundfontPath,jstring jOutputWavPath,jstring jMidiPath,jint jChannel) {
    fluid_settings_t* settings;
    fluid_synth_t* synth;
    fluid_player_t* player;
    fluid_file_renderer_t* renderer;

    settings = new_fluid_settings();

    // specify the file to store the audio to
    const char* outputWavPath = env->GetStringUTFChars(jOutputWavPath,nullptr);
    fluid_settings_setstr(settings,"audio.file.name",outputWavPath);

    // since this is a non-realtime scenario,there is no need to pin the sample data
    fluid_settings_setint(settings,"synth.lock-memory",0);

    synth = new_fluid_synth(settings);

    // set basic channel
    fluid_synth_reset_basic_channel(synth,-1);
    fluid_synth_set_basic_channel(synth,jChannel,FLUID_CHANNEL_MODE_OMNION_MONO,1);

    // Load sample soundfont
    const char* soundfontPath = env->GetStringUTFChars(jSoundfontPath,nullptr);
    fluid_synth_sfload(synth,soundfontPath,1);

    const char* midiPath = env->GetStringUTFChars(jMidiPath,nullptr);
    player = new_fluid_player(synth);
    fluid_player_add(player,midiPath);
    fluid_player_play(player);

    renderer = new_fluid_file_renderer (synth);
    while (fluid_player_get_status(player) == FLUID_PLAYER_PLAYING)
    {
        if (fluid_file_renderer_process_block(renderer) != FLUID_OK)
        {
            break;
        }
    }

    // just for sure: stop the playback explicitly and wait until finished
    fluid_player_stop(player);
    fluid_player_join(player);

    delete_fluid_file_renderer(renderer);
    delete_fluid_player(player);
    delete_fluid_synth(synth);
    delete_fluid_settings(settings);
}

注意这两行：

fluid_synth_reset_basic_channel(synth,-1);
fluid_synth_set_basic_channel(synth,1);

jChannel是Midi通道号（1-16）。我不确定自己是否做对了。

有人可以告诉我如何将1个Midi通道准确转换为wav吗？上面的代码会转换单个频道吗？

预先感谢

解决方法

对于后代，以下是在Android上将单个Midi通道转换为wav的方法：

#include <jni.h>
#include <string>
#include <fluidsynth.h>
#include <unistd.h>

// default channel to export
int channelToExport = 0;

int handle_midi_event(void* data,fluid_midi_event_t* event)
{
    // successfully handles midi event from player to synthesizer only if midi event is in the exported channel
    return fluid_midi_event_get_channel(event) == channelToExport ? fluid_synth_handle_midi_event(data,event) : FLUID_FAILED;
}

extern "C" JNIEXPORT void JNICALL Java_com_ryzhak_midi2wavconverter_MainActivity_convertMidiToWav(JNIEnv* env,jobject,jstring jSoundfontPath,jstring jOutputWavPath,jstring jMidiPath,jint jChannel) {
    fluid_settings_t* settings;
    fluid_synth_t* synth;
    fluid_player_t* player;
    fluid_file_renderer_t* renderer;

    settings = new_fluid_settings();

    // specify the file to store the audio to
    const char* outputWavPath = env->GetStringUTFChars(jOutputWavPath,nullptr);
    fluid_settings_setstr(settings,"audio.file.name",outputWavPath);

    // since this is a non-realtime scenario,there is no need to pin the sample data
    fluid_settings_setint(settings,"synth.lock-memory",0);

    synth = new_fluid_synth(settings);

    // Load sample soundfont
    const char* soundfontPath = env->GetStringUTFChars(jSoundfontPath,nullptr);
    fluid_synth_sfload(synth,soundfontPath,1);

    // create a new player
    const char* midiPath = env->GetStringUTFChars(jMidiPath,nullptr);
    player = new_fluid_player(synth);
    fluid_player_add(player,midiPath);
    fluid_player_play(player);

    // set basic channel to export
    channelToExport = jChannel;
    fluid_player_set_playback_callback(player,handle_midi_event,synth);

    // start conversion
    renderer = new_fluid_file_renderer (synth);
    while (fluid_player_get_status(player) == FLUID_PLAYER_PLAYING)
    {
        if (fluid_file_renderer_process_block(renderer) != FLUID_OK)
        {
            break;
        }
    }

    // just for sure: stop the playback explicitly and wait until finished
    fluid_player_stop(player);
    fluid_player_join(player);

    delete_fluid_file_renderer(renderer);
    delete_fluid_player(player);
    delete_fluid_synth(synth);
    delete_fluid_settings(settings);
}