diff --git a/src/midi.android.c b/src/midi.android.c
index 54d6d0f..0001a82 100644
--- a/src/midi.android.c
+++ b/src/midi.android.c
@@ -23,58 +23,25 @@
 #include "portab.h"
 #include "midi.h"
 
-static int midi_initialize(int subdev);
-static int midi_exit(void);
-static int midi_reset(void);
-static int midi_start(int no, int loop, char *data, int datalen);
-static int midi_stop();
-static int midi_pause(void);
-static int midi_unpause(void);
-static int midi_get_playing_info(midiplaystate *st);
-static int midi_getflag(int mode, int index);
-static int midi_setflag(int mode, int index, int val);
-static int midi_setvol(int vol);
-static int midi_getvol();
-static int midi_fadestart(int time, int volume, int stop);
-static bool midi_fading();
+static void midi_stop(void);
 
-#define midi midi_android
-mididevice_t midi = {
-	midi_initialize,
-	midi_exit,
-	midi_reset,
-	midi_start,
-	midi_stop,
-	midi_pause,
-	midi_unpause,
-	midi_get_playing_info,
-	midi_getflag,
-	midi_setflag,
-	midi_setvol,
-	midi_getvol,
-	midi_fadestart,
-	midi_fading
-};
-
-static int midi_initialize(int subdev) {
-	return OK;
+static bool midi_initialize(int subdev) {
+	return true;
 }
 
-static int midi_exit(void) {
+static void midi_exit(void) {
 	midi_stop();
-	return OK;
 }
 
-static int midi_reset(void) {
+static void midi_reset(void) {
 	midi_stop();
-	return OK;
 }
 
-static int midi_start(int no, int loop, char *data, int datalen) {
+static bool midi_start(int no, int loop, const uint8_t *data, int datalen) {
 	JNIEnv *env = SDL_AndroidGetJNIEnv();
 	if ((*env)->PushLocalFrame(env, 16) < 0) {
 		WARNING("Failed to allocate JVM local references");
-		return NG;
+		return false;
 	}
 
 	char path[PATH_MAX];
@@ -83,7 +50,7 @@ static int midi_start(int no, int loop, char *data, int datalen) {
 	if (!fp) {
 		WARNING("Failed to create temporary file");
 		(*env)->PopLocalFrame(env, NULL);
-		return NG;
+		return false;
 	}
 	fwrite(data, datalen, 1, fp);
 	fclose(fp);
@@ -92,7 +59,7 @@ static int midi_start(int no, int loop, char *data, int datalen) {
 	if (!path_str) {
 		WARNING("Failed to allocate a string");
 		(*env)->PopLocalFrame(env, NULL);
-		return NG;
+		return false;
 	}
 
 	jobject context = SDL_AndroidGetActivity();
@@ -101,40 +68,38 @@ static int midi_start(int no, int loop, char *data, int datalen) {
 	(*env)->CallVoidMethod(env, context, mid, path_str, loop == 0);
 	(*env)->PopLocalFrame(env, NULL);
 
-	return OK;
+	return true;
 }
 
-static int midi_stop() {
+static void midi_stop(void) {
 	JNIEnv *env = SDL_AndroidGetJNIEnv();
 	if ((*env)->PushLocalFrame(env, 16) < 0) {
 		WARNING("Failed to allocate JVM local references");
-		return NG;
+		return;
 	}
 	jobject context = SDL_AndroidGetActivity();
 	jmethodID mid = (*env)->GetMethodID(env, (*env)->GetObjectClass(env, context),
 										"midiStop", "()V");
 	(*env)->CallVoidMethod(env, context, mid);
 	(*env)->PopLocalFrame(env, NULL);
-
-	return OK;
 }
 
-static int midi_pause(void) {
-	return NG; // FIXME
+static void midi_pause(void) {
+	// FIXME
 }
 
-static int midi_unpause(void) {
-	return NG; // FIXME
+static void midi_unpause(void) {
+	// FIXME
 }
 
-static int midi_get_playing_info(midiplaystate *st) {
+static bool midi_get_playing_info(midiplaystate *st) {
 	st->in_play = false;
 	st->loc_ms  = 0;
 
 	JNIEnv *env = SDL_AndroidGetJNIEnv();
 	if ((*env)->PushLocalFrame(env, 16) < 0) {
 		WARNING("Failed to allocate JVM local references");
-		return NG;
+		return false;
 	}
 	jobject context = SDL_AndroidGetActivity();
 	jmethodID mid = (*env)->GetMethodID(env, (*env)->GetObjectClass(env, context),
@@ -146,29 +111,36 @@ static int midi_get_playing_info(midiplaystate *st) {
 		st->in_play = true;
 		st->loc_ms = pos;
 	}
-	return OK;
+	return true;
 }
 
 static int midi_getflag(int mode, int index) {
 	return 0;
 }
 
-static int midi_setflag(int mode, int index, int val) {
-	return NG;
+static bool midi_setflag(int mode, int index, int val) {
+	return false;
 }
 
-static int midi_setvol(int vol) {
-	return NG; // FIXME
-}
-
-static int midi_getvol() {
-	return 100; // FIXME
-}
-
-static int midi_fadestart(int time, int volume, int stop) {
-	return NG; // FIXME
-}
-
-static bool midi_fading() {
+static bool midi_fadestart(int time, int volume, int stop) {
 	return false; // FIXME
 }
+
+static bool midi_fading(void) {
+	return false; // FIXME
+}
+
+mididevice_t midi_android = {
+	.init = midi_initialize,
+	.exit = midi_exit,
+	.reset = midi_reset,
+	.start = midi_start,
+	.stop = midi_stop,
+	.pause = midi_pause,
+	.unpause = midi_unpause,
+	.getpos = midi_get_playing_info,
+	.getflag = midi_getflag,
+	.setflag = midi_setflag,
+	.fadestart = midi_fadestart,
+	.fading = midi_fading,
+};
diff --git a/src/midi.c b/src/midi.c
index 4769929..6acf136 100644
--- a/src/midi.c
+++ b/src/midi.c
@@ -47,8 +47,8 @@ extern mididevice_t midi_sdlmixer;
 extern mididevice_t midi_portmidi;
 #endif
 
-int midi_init(mididevice_t *midi) {
-	int ret = NG;
+bool midi_init(mididevice_t *midi) {
+	bool ret = false;
 
 	switch(default_mode) {
 	case 'e':
diff --git a/src/midi.emscripten.c b/src/midi.emscripten.c
index e35711e..e100849 100644
--- a/src/midi.emscripten.c
+++ b/src/midi.emscripten.c
@@ -24,90 +24,75 @@
 #include "portab.h"
 #include "midi.h"
 
-static int midi_initialize(int subdev) {
-	return OK;
+static bool midi_initialize(int subdev) {
+	return true;
 }
 
-EM_JS(int, midi_stop, (void), {
+EM_JS(void, midi_stop, (void), {
 	xsystem35.midiPlayer.stop();
-	return xsystem35.Status.OK;
 });
 
-static int midi_exit(void) {
+static void midi_exit(void) {
 	midi_stop();
-	return OK;
 }
 
-static int midi_reset(void) {
+static void midi_reset(void) {
 	midi_stop();
-	return OK;
 }
 
-static int midi_start(int no, int loop, char *data, int datalen) {
+static bool midi_start(int no, int loop, const uint8_t *data, int datalen) {
 	EM_ASM_ARGS({ xsystem35.midiPlayer.play($0, $1, $2); }, loop, data, datalen);
-	return OK;
+	return true;
 }
 
-EM_JS(int, midi_pause, (void), {
+EM_JS(void, midi_pause, (void), {
 	xsystem35.midiPlayer.pause();
-	return xsystem35.Status.OK;
 });
 
-EM_JS(int, midi_unpause, (void), {
+EM_JS(void, midi_unpause, (void), {
 	xsystem35.midiPlayer.resume();
-	return xsystem35.Status.OK;
 });
 
-static int midi_get_playing_info(midiplaystate *st) {
+static bool midi_get_playing_info(midiplaystate *st) {
 	int pos = EM_ASM_INT_V( return xsystem35.midiPlayer.getPosition(); );
 	if (pos >= 0) {
 		st->in_play = true;
 		st->loc_ms = pos;
-		return OK;
+		return true;
 	}
 	st->in_play = false;
 	st->loc_ms  = 0;
-	return OK;
+	return true;
 }
 
 static int midi_getflag(int mode, int index) {
 	return 0;
 }
 
-static int midi_setflag(int mode, int index, int val) {
-	return NG;
+static bool midi_setflag(int mode, int index, int val) {
+	return false;
 }
 
-EM_JS(int, midi_setvol, (int vol), {
-	xsystem35.midiPlayer.setVolume(vol);
-	return xsystem35.Status.OK;
+EM_JS(bool, midi_fadestart, (int time, int volume, int stop), {
+	xsystem35.midiPlayer.fadeStart(time, volume, stop);
+	return 1;
 });
 
-EM_JS(int, midi_getvol,(), {
-	return xsystem35.midiPlayer.getVolume();
-});
-
-EM_JS(int, midi_fadestart, (int time, int volume, int stop), {
-	return xsystem35.midiPlayer.fadeStart(time, volume, stop);
-});
-
-EM_JS(bool, midi_fading, (), {
+EM_JS(bool, midi_fading, (void), {
 	return xsystem35.midiPlayer.isFading();
 });
 
 mididevice_t midi_emscripten = {
-	midi_initialize,
-	midi_exit,
-	midi_reset,
-	midi_start,
-	midi_stop,
-	midi_pause,
-	midi_unpause,
-	midi_get_playing_info,
-	midi_getflag,
-	midi_setflag,
-	midi_setvol,
-	midi_getvol,
-	midi_fadestart,
-	midi_fading
+	.init = midi_initialize,
+	.exit = midi_exit,
+	.reset = midi_reset,
+	.start = midi_start,
+	.stop = midi_stop,
+	.pause = midi_pause,
+	.unpause = midi_unpause,
+	.getpos = midi_get_playing_info,
+	.getflag = midi_getflag,
+	.setflag = midi_setflag,
+	.fadestart = midi_fadestart,
+	.fading = midi_fading,
 };
diff --git a/src/midi.h b/src/midi.h
index ef63770..e9d8fee 100644
--- a/src/midi.h
+++ b/src/midi.h
@@ -24,7 +24,8 @@
 #ifndef __MIDI_H__
 #define __MIDI_H__
 
-#include "portab.h"
+#include <stdbool.h>
+#include <stdint.h>
 
 typedef struct {
 	bool in_play; /* now playing ? */
@@ -32,26 +33,23 @@ typedef struct {
 	int play_no;     /* current playing no */
 } midiplaystate;
 
-typedef struct mididevice mididevice_t;
-struct mididevice {
-	int  (* init)(int);
-	int  (* exit)(void);
-	int  (* reset)(void);
+typedef struct {
+	bool (*init)(int);
+	void (*exit)(void);
+	void (*reset)(void);
 	// Play through the music loop times. If loop == 0, loops forever.
-	int  (* start)(int no, int loop, char *data, int datalen);
-	int  (* stop)(void);
-	int  (* pause)(void);
-	int  (* unpause)(void);
-	int  (* getpos)(midiplaystate *);
-	int  (* getflag)(int mode, int index);
-	int  (* setflag)(int mode, int index, int val);
-	int  (* setvol)(int);
-	int  (* getvol)(int);
-	int  (* fadestart)(int time, int volume, int stop);
-	bool (* fading)();
-};
+	bool (*start)(int no, int loop, const uint8_t *data, int datalen);
+	void (*stop)(void);
+	void (*pause)(void);
+	void (*unpause)(void);
+	bool (*getpos)(midiplaystate *);
+	int (*getflag)(int mode, int index);
+	bool (*setflag)(int mode, int index, int val);
+	bool (*fadestart)(int time, int volume, int stop);
+	bool (*fading)(void);
+} mididevice_t;
 
-extern int  midi_init(mididevice_t *);
-extern void midi_set_output_device(int mode);
+bool midi_init(mididevice_t *);
+void midi_set_output_device(int mode);
 
 #endif /* __MIDI_H__ */
diff --git a/src/midi.portmidi.c b/src/midi.portmidi.c
index c5e6e6b..599b9bf 100644
--- a/src/midi.portmidi.c
+++ b/src/midi.portmidi.c
@@ -42,33 +42,7 @@ static struct {
 	char midi_flag[128];
 } flags;
 
-static int midi_initialize(int subdev);
-static int midi_exit(void);
-static int midi_reset(void);
-static int midi_start(int no, int loop, char *data, int datalen);
-static int midi_stop(void);
-static int midi_pause(void);
-static int midi_unpause(void);
-static int midi_getpos(midiplaystate *st);
-static int midi_getflag(int mode, int index);
-static int midi_setflag(int mode, int index, int val);
-
-mididevice_t midi_portmidi = {
-	midi_initialize,
-	midi_exit,
-	midi_reset,
-	midi_start,
-	midi_stop,
-	midi_pause,
-	midi_unpause,
-	midi_getpos,
-	midi_getflag,
-	midi_setflag,
-	NULL,
-	NULL,
-	NULL,
-	NULL
-};
+static void midi_stop(void);
 
 enum midi_command {
 	CMD_PLAY,
@@ -233,7 +207,7 @@ static void midi_playloop(PortMidiStream *stream, struct midiinfo *midi) {
 	}
 }
 
-static int midi_thread(void*) {
+static int midi_thread(void* unused) {
 	PortMidiStream *stream;
 	PmError err = Pm_OpenOutput(&stream, device_id, NULL, 0, midi_time_proc, NULL, MIDI_LATENCY);
 	if (err != pmNoError) {
@@ -272,11 +246,11 @@ static int midi_thread(void*) {
 	}
 }
 
-static int midi_initialize(int subdev) {
+static bool midi_initialize(int subdev) {
 	PmError err = Pm_Initialize();
 	if (err != pmNoError) {
 		WARNING("%s", Pm_GetErrorText(err));
-		return NG;
+		return false;
 	}
 
 	int ndevices = Pm_CountDevices();
@@ -287,14 +261,14 @@ static int midi_initialize(int subdev) {
 	}
 	if (subdev < 0 || subdev >= ndevices) {
 		WARNING("invalid midi device number");
-		return NG;
+		return false;
 	}
 
 	device_id = subdev;
-	return OK;
+	return true;
 }
 
-static int midi_exit(void) {
+static void midi_exit(void) {
 	if (queue) {
 		ENQUEUE(CMD_STOP);
 		ENQUEUE(CMD_QUIT);
@@ -304,16 +278,14 @@ static int midi_exit(void) {
 		queue = NULL;
 	}
 	Pm_Terminate();
-	return OK;
 }
 
-static int midi_reset(void) {
+static void midi_reset(void) {
 	midi_stop();
-	return OK;
 }
 
 /* no = 0~ */
-static int midi_start(int no, int loop, char *data, int datalen) {
+static bool midi_start(int no, int loop, const uint8_t *data, int datalen) {
 	static int seq = 0;
 
 	if (queue) {
@@ -326,47 +298,44 @@ static int midi_start(int no, int loop, char *data, int datalen) {
 	struct midiinfo *midi = mf_read_midifile(data, datalen);
 	if (!midi) {
 		WARNING("error reading midi file");
-		return NG;
+		return false;
 	}
 	SDL_AtomicSet(&atomic_seq, ++seq);
 	ENQUEUE(CMD_PLAY, seq, midi);
 
 	start_time = SDL_GetTicks();
 
-	return OK;
+	return true;
 }
 
-static int midi_stop(void) {
+static void midi_stop(void) {
 	if (queue) {
 		SDL_AtomicSet(&atomic_seq, 0);
 		ENQUEUE(CMD_STOP);
 	}
-	return OK;
 }
 
-static int midi_pause(void) {
+static void midi_pause(void) {
 	if (queue)
 		ENQUEUE(CMD_PAUSE);
-	return OK;
 }
 
-static int midi_unpause(void) {
+static void midi_unpause(void) {
 	if (queue)
 		ENQUEUE(CMD_UNPAUSE);
-	return OK;
 }
 
-static int midi_getpos(midiplaystate *st) {
+static bool midi_get_playing_info(midiplaystate *st) {
 	if (SDL_AtomicGet(&atomic_seq) == 0) {
 		st->in_play = false;
 		st->loc_ms  = 0;
-		return OK;
+		return true;
 	}
 
 	st->in_play = true;
 	st->loc_ms = SDL_GetTicks() - start_time;
 
-	return OK;
+	return true;
 }
 
 static int midi_getflag(int mode, int index) {
@@ -379,7 +348,7 @@ static int midi_getflag(int mode, int index) {
 	}
 }
 
-static int midi_setflag(int mode, int index, int val) {
+static bool midi_setflag(int mode, int index, int val) {
 	if (mode == 0) {
 		/* flag */
 		flags.midi_flag[index] = val;
@@ -387,5 +356,20 @@ static int midi_setflag(int mode, int index, int val) {
 		/* variable */
 		flags.midi_variable[index] = val;
 	}
-	return OK;
+	return true;
 }
+
+mididevice_t midi_portmidi = {
+	.init = midi_initialize,
+	.exit = midi_exit,
+	.reset = midi_reset,
+	.start = midi_start,
+	.stop = midi_stop,
+	.pause = midi_pause,
+	.unpause = midi_unpause,
+	.getpos = midi_get_playing_info,
+	.getflag = midi_getflag,
+	.setflag = midi_setflag,
+	.fadestart = NULL,
+	.fading = NULL,
+};
diff --git a/src/midi.sdlmixer.c b/src/midi.sdlmixer.c
index 162e7d7..e47867c 100644
--- a/src/midi.sdlmixer.c
+++ b/src/midi.sdlmixer.c
@@ -31,146 +31,116 @@
 #define MIX_INIT_MID MIX_INIT_FLUIDSYNTH
 #endif
 
-static int midi_initialize(int subdev);
-static int midi_exit(void);
-static int midi_reset(void);
-static int midi_start(int no, int loop, char *data, int datalen);
-static int midi_stop();
-static int midi_pause(void);
-static int midi_unpause(void);
-static int midi_get_playing_info(midiplaystate *st);
-static int midi_getflag(int mode, int index);
-static int midi_setflag(int mode, int index, int val);
-static int midi_setvol(int vol);
-static int midi_getvol();
-static int midi_fadestart(int time, int volume, int stop);
-static bool midi_fading();
-
-#define midi midi_sdlmixer
-mididevice_t midi = {
-	midi_initialize,
-	midi_exit,
-	midi_reset,
-	midi_start,
-	midi_stop,
-	midi_pause,
-	midi_unpause,
-	midi_get_playing_info,
-	midi_getflag,
-	midi_setflag,
-	midi_setvol,
-	midi_getvol,
-	midi_fadestart,
-	midi_fading
-};
+static void midi_stop(void);
 
 static Mix_Music *mix_music;
 static int start_time;
 static uint32_t fade_tick;
 
-static int midi_initialize(int subdev) {
+static bool midi_initialize(int subdev) {
 	if (Mix_Init(MIX_INIT_MID) != MIX_INIT_MID)
-		return NG;
-	return OK;
+		return false;
+	return true;
 }
 
-static int midi_exit(void) {
+static void midi_exit(void) {
 	Mix_Quit();
-	return OK;
 }
 
-static int midi_reset(void) {
+static void midi_reset(void) {
 	midi_stop();
-	return OK;
 }
 
-static int midi_start(int no, int loop, char *data, int datalen) {
+static bool midi_start(int no, int loop, const uint8_t *data, int datalen) {
 	midi_stop();
 
 	SDL_RWops *rwops = SDL_RWFromConstMem(data, datalen);
 	mix_music = Mix_LoadMUSType_RW(rwops, MUS_MID, SDL_TRUE /* freesrc */);
 	if (!mix_music) {
 		WARNING("Cannot load MIDI: %s", SDL_GetError());
-		return NG;
+		return false;
 	}
 
 	if (Mix_PlayMusic(mix_music, loop ? loop : -1) != 0) {
 		WARNING("Cannot play MIDI: %s", SDL_GetError());
 		Mix_FreeMusic(mix_music);
 		mix_music = NULL;
-		return NG;
+		return false;
 	}
 
 	start_time = SDL_GetTicks();
-	return OK;
+	return true;
 }
 
-static int midi_stop() {
+static void midi_stop() {
 	if (!mix_music)
-		return OK;
+		return;
 	Mix_FreeMusic(mix_music);
 	mix_music = NULL;
-	return OK;
 }
 
-static int midi_pause(void) {
+static void midi_pause(void) {
 	// FIXME: adjust start_time
 	Mix_PauseMusic();
-	return OK;
 }
 
-static int midi_unpause(void) {
+static void midi_unpause(void) {
 	// FIXME: adjust start_time
 	Mix_ResumeMusic();
-	return OK;
 }
 
-static int midi_get_playing_info(midiplaystate *st) {
+static bool midi_get_playing_info(midiplaystate *st) {
 	if (!mix_music || !Mix_PlayingMusic()) {
 		st->in_play = false;
 		st->loc_ms  = 0;
-		return OK;
+		return true;
 	}
 
 	st->in_play = true;
 	st->loc_ms = SDL_GetTicks() - start_time;
-	return OK;
+	return true;
 }
 
 static int midi_getflag(int mode, int index) {
 	return 0;
 }
 
-static int midi_setflag(int mode, int index, int val) {
-	return NG;
+static bool midi_setflag(int mode, int index, int val) {
+	return false;
 }
 
-static int midi_setvol(int vol) {
-	Mix_VolumeMusic(vol * MIX_MAX_VOLUME / 100);
-	return OK;
-}
-
-static int midi_getvol() {
-	return Mix_VolumeMusic(-1) * 100 / MIX_MAX_VOLUME;
-}
-
-static int midi_fadestart(int time, int volume, int stop) {
+static bool midi_fadestart(int time, int volume, int stop) {
 	if (time == 0) {
-		midi_setvol(volume);
+		Mix_VolumeMusic(volume * MIX_MAX_VOLUME / 100);
 		if (stop)
 			midi_stop();
-		return OK;
+		return true;
 	}
 
 	if (volume == 0) {
 		Mix_FadeOutMusic(time);  // FIXME: this always stops the music
 		fade_tick = SDL_GetTicks() + time;
-		return OK;
+		return true;
 	}
 	WARNING("(time=%d, volume=%d, stop=%d) unsupported", time, volume, stop);
-	return NG;
+	return false;
 }
 
-static bool midi_fading() {
+static bool midi_fading(void) {
 	return SDL_GetTicks() < fade_tick;
 }
+
+mididevice_t midi_sdlmixer = {
+	.init = midi_initialize,
+	.exit = midi_exit,
+	.reset = midi_reset,
+	.start = midi_start,
+	.stop = midi_stop,
+	.pause = midi_pause,
+	.unpause = midi_unpause,
+	.getpos = midi_get_playing_info,
+	.getflag = midi_getflag,
+	.setflag = midi_setflag,
+	.fadestart = midi_fadestart,
+	.fading = midi_fading,
+};
diff --git a/src/midifile.c b/src/midifile.c
index 4a314ad..c2263eb 100644
--- a/src/midifile.c
+++ b/src/midifile.c
@@ -47,8 +47,8 @@
 #define META_SET_TEMPO 0x51
 
 struct stream {
-	uint8_t *p;
-	uint8_t *end;
+	const uint8_t *p;
+	const uint8_t *end;
 };
 
 static inline uint8_t read8(struct stream *input) {
@@ -269,7 +269,7 @@ static bool read_header(struct midiinfo *midi, struct stream *input) {
 	return true;
 }
 
-struct midiinfo *mf_read_midifile(uint8_t *data, size_t len) {
+struct midiinfo *mf_read_midifile(const uint8_t *data, size_t len) {
 	struct stream input = { .p = data, .end = data + len };
 	struct midiinfo *midi = calloc(1, sizeof(struct midiinfo));
 
diff --git a/src/midifile.h b/src/midifile.h
index 599ef43..921cbca 100644
--- a/src/midifile.h
+++ b/src/midifile.h
@@ -60,7 +60,7 @@ struct midiinfo {
 	int sys35_label[128]; /* system35 jump info */
 };
 
-extern struct midiinfo *mf_read_midifile(uint8_t *stream, size_t len);
+extern struct midiinfo *mf_read_midifile(const uint8_t *stream, size_t len);
 extern void mf_remove_midifile(struct midiinfo *m);
 
 #endif /* __MIDIFILE_H__ */
diff --git a/src/music_midi.c b/src/music_midi.c
index 3440dae..404fcb2 100644
--- a/src/music_midi.c
+++ b/src/music_midi.c
@@ -30,9 +30,7 @@
 #include "ald_manager.h"
 
 int musmidi_init(void) {
-	int st = midi_init(&prv.mididev);
-
-	if (st == -1) {
+	if (!midi_init(&prv.mididev)) {
 		prv.midi_valid = false;
 		return NG;
 	} else {
@@ -65,7 +63,10 @@ int musmidi_start(int no, int loop) {
 	if (dfile == NULL)
 		return NG;
 	
-	prv.mididev.start(no, loop, dfile->data, dfile->size);
+	if (!prv.mididev.start(no, loop, dfile->data, dfile->size)) {
+		ald_freedata(dfile);
+		return NG;
+	}
 
 	if (prv.midi_dfile)
 		ald_freedata(prv.midi_dfile);
@@ -117,8 +118,7 @@ midiplaystate musmidi_getpos(void) {
 int musmidi_setflag(int mode, int index, int val) {
 	if (!prv.midi_valid) return NG;
 
-	prv.mididev.setflag(mode, index, val);
-	return OK;
+	return prv.mididev.setflag(mode, index, val) ? OK : NG;
 }
 
 int musmidi_getflag(int mode, int index) {
@@ -132,7 +132,7 @@ int musmidi_fadestart(int time, int volume, int stop) {
 
 	if (!prv.mididev.fadestart)
 		return NG;
-	return prv.mididev.fadestart(time, volume, stop);
+	return prv.mididev.fadestart(time, volume, stop) ? OK : NG;
 }
 
 bool musmidi_fading(void) {