[fluid-dev] fluidsynth export single midi channel to wav

[Владимир Рыжак]

Hi!

I'm very new to the music tech so bear with me.

There are 16 channels in a midi file. I'm trying to convert only 1 channel from a midi file to wav.

Here is how it works now:

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);
}

Notice these 2 lines:

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

jChannel is the midi channel number(1-16). I'm not really sure whether I'm doing it right.

Could somebody tell me how to convert exactly 1 midi channel to wav? Does the above code convert only a single channel?

Thanks in advance