I've recently run into a problem with audio playback in Allegro 5.1.8: audio stream playback lags behind the clock by a factor of about 0.0000205. That might not sound like a lot, but it's significant in my case as I am working on a rhythm game. After ten minutes the audio and clock are out of sync by about 12 milliseconds, more than enough to make the rhythm element unusable.
This lag doesn't appear to depend on the stream I'm playing, its sample rate, the buffer size or count (as long as they're adequate to prevent buffer underflow), or the file format.
I have only tested this on Mac OS 10.9 so far, but at the bottom of this post I have included a test case I wrote. The "total drift" and "drift per second" displays will start out rather chaotic, but over time the total drift will gradually creep up and the drift per second will eventually converge to somewhere around 0.00002. I'd like to ask the following of other developers:
- Would you please run this test case yourself on other platforms and see if you get similar results? The longer it runs, the more accurate the drift per second figure will be. The white flash and the cymbal crash in the test loop become visibly out of sync after a half hour or so as well.
- Do you have any idea what the cause of this problem might be or, better yet, how to fix it?
The audio stream I used for the test case is attached to this post, but feel free to try other files. The font DejaVuSans.ttf can be found here.
#SelectExpand
1//////////////////////////////////////////////////////////////////////
2// Test case for audio drift in allegro 5.1.8. By Donald Goldin. //
3//////////////////////////////////////////////////////////////////////
4
5#include <allegro5/allegro.h>
6#include <allegro5/allegro_audio.h>
7#include <allegro5/allegro_acodec.h>
8#include <allegro5/allegro_font.h>
9#include <allegro5/allegro_ttf.h>
10#include <math.h>
11
12// The results of this test case are similar whether or not USE_PLAYED_SAMPLES is
13// defined, but getStreamTime is much more precise with USE_PLAYED_SAMPLES and
14// thus the drift per second measurement will converge more quickly
15
16#define USE_PLAYED_SAMPLES
17
18double getStreamTime
(ALLEGRO_AUDIO_STREAM * stream
)
19{
20#ifdef USE_PLAYED_SAMPLES
21 uint64_t samples
= al_get_audio_stream_played_samples
(stream
);
22 double syncTime
= samples
/ ((double)al_get_audio_stream_frequency(stream
));
23 return syncTime
;
24#else
25 return al_get_audio_stream_position_secs(stream
);
26#endif
27}
28
29double arrayAverage
(double * array,
size_t arraySize
)
30{
31 if (arraySize
== 0)
32 {
33 return 0.
0;
34 }
35 else
36 {
37 double total
= 0.
0;
38 for (size_t i
= 0; i
< arraySize
; i
++)
39 {
40 total
+= array
[i
];
41 }
42 return total
/ arraySize
;
43 }
44}
45
46int main
(int,
char**);
47
48int main
(int argc,
char** argv
)
49{
50 // initialization
51 if (!al_init())
52 {
53 printf("al_init failed!\n");
54 return 1;
55 }
56
57 if (!al_install_audio())
58 {
59 printf("error: couldn't install audio\n");
60 return 1;
61 }
62
63 if (!al_init_acodec_addon())
64 {
65 printf("error: couldn't init acodec addon\n");
66 return 1;
67 }
68
69 if (!al_reserve_samples(16))
70 {
71 printf("error: couldn't reserve samples\n");
72 return 1;
73 }
74
75 if (!al_install_keyboard())
76 {
77 printf("error: couldn't install keyboard\n");
78 return 1;
79 }
80
81 if (!al_init_font_addon())
82 {
83 printf("error: couldn't init font addon\n");
84 return 1;
85 }
86
87 if (!al_init_ttf_addon())
88 {
89 printf("error: couldn't init ttf addon\n");
90 return 1;
91 }
92
93 ALLEGRO_FONT * font = al_load_ttf_font("DejaVuSans.ttf",
10,
0);
94
95 al_set_new_display_option(ALLEGRO_VSYNC,
1, ALLEGRO_SUGGEST
);
96 ALLEGRO_DISPLAY * display
= al_create_display(640,
480);
97 if (display
== NULL
)
98 {
99 printf("error: could not create display\n");
100 }
101
102 ALLEGRO_MIXER * mixer
= al_get_default_mixer();
103
104 if (!mixer
)
105 {
106 printf("error: couldn't get default mixer\n");
107 return 1;
108 }
109
110 ALLEGRO_AUDIO_STREAM * stream
= al_load_audio_stream("TestStream.ogg",
4,
1024);
111
112 const double k_loopLength
= 8.
0;
113
114 if (stream
== NULL
)
115 {
116 printf("error: failed to load stream\n");
117 return 1;
118 }
119 al_attach_audio_stream_to_mixer(stream, mixer
);
120 al_set_audio_stream_gain(stream,
1.
0);
121 al_set_audio_stream_playmode(stream, ALLEGRO_PLAYMODE_LOOP
);
122 al_set_audio_stream_loop_secs(stream,
0.
0, k_loopLength
);
123 al_set_audio_stream_playing(stream,
true);
124
125 al_rest(2.
0); // give the stream a couple seconds to buffer
126
127 if (!al_get_audio_stream_playing(stream
))
128 {
129 printf("error: stream isn't playing\n");
130 return 1;
131 }
132
133 double startTime
= al_get_time();
134 double initialOffset
= getStreamTime
(stream
) - startTime
;
135
136 bool shouldExit
= false;
137 ALLEGRO_KEYBOARD_STATE kbState
;
138
139 char buf
[128];
140
141 ALLEGRO_EVENT_QUEUE * queue
= al_create_event_queue();
142 ALLEGRO_TIMER * timer
= al_create_timer(1.
0 / 60.
0);
143 al_register_event_source(queue,
al_get_timer_event_source(timer
));
144 al_register_event_source(queue,
al_get_display_event_source(display
));
145 al_start_timer(timer
);
146
147 ALLEGRO_EVENT event
;
148
149 const size_t k_historySize
= 60;
150 double driftHistory
[k_historySize
];
151 for (size_t i
= 0; i
< k_historySize
; i
++)
152 {
153 driftHistory
[i
] = 0.
0;
154 }
155 size_t historyPos
= 0;
156
157 // main update loop
158 while (!shouldExit
)
159 {
160 bool needsUpdate
= false;
161
162 al_wait_for_event(queue,
&event
);
163
164 switch (event.type
)
165 {
166 case ALLEGRO_EVENT_DISPLAY_CLOSE:
167 if (event.display.source
== display
)
168 {
169 shouldExit
= true;
170 }
171 break;
172 case ALLEGRO_EVENT_TIMER:
173 if (event.timer.source
== timer
)
174 {
175 needsUpdate
= true;
176 }
177 break;
178 default:
179 break;
180 }
181
182 if (needsUpdate
)
183 {
184 al_get_keyboard_state(&kbState
);
185 if (al_key_down(&kbState, ALLEGRO_KEY_Q
))
186 {
187 shouldExit
= true;
188 }
189
190 if (al_key_down(&kbState, ALLEGRO_KEY_R
))
191 {
192 startTime
= al_get_time();
193 initialOffset
= getStreamTime
(stream
) - startTime
;
194 }
195
196 if (al_key_down(&kbState, ALLEGRO_KEY_M
))
197 {
198 al_set_audio_stream_gain(stream,
0.
0);
199 }
200
201 if (al_key_down(&kbState, ALLEGRO_KEY_N
))
202 {
203 al_set_audio_stream_gain(stream,
1.
0);
204 }
205
206 double clockTime
= al_get_time();
207 double streamTime
= getStreamTime
(stream
);
208
209#ifdef USE_PLAYED_SAMPLES
210 double clockTimeLooped
= initialOffset
+ clockTime
;
211#else
212 double clockTimeLooped
= initialOffset
+ clockTime
- floor((initialOffset
+ clockTime
) / k_loopLength
) * k_loopLength
;
213#endif
214
215 driftHistory
[historyPos
] = clockTimeLooped
- streamTime
;
216 historyPos
++;
217 if (historyPos
== k_historySize
)
218 {
219 historyPos
= 0;
220 }
221
222 double totalDrift
= arrayAverage
(driftHistory, k_historySize
);
223 double driftPerSecond
= totalDrift
/ (clockTime
- startTime
);
224
225#ifdef USE_PLAYED_SAMPLES
226 if (clockTimeLooped
- floor(clockTimeLooped
/ k_loopLength
) * k_loopLength
< 0.
125)
227#else
228 if (clockTimeLooped
< 0.
125)
229#endif
230 {
231 al_clear_to_color(al_map_rgb_f(1.f,
1.f,
1.f
));
232 }
233 else
234 {
235 al_clear_to_color(al_map_rgb_f(0.f,
0.f,
0.f
));
236 }
237
238 snprintf(buf,
128,
"time elapsed: %f", clockTime
- startTime
);
239 al_draw_text(font,
al_map_rgb_f(0.f,
0.
5f,
0.f
),
24,
8,
0, buf
);
240
241 snprintf(buf,
128,
"playback time according to clock: %f", clockTimeLooped
);
242 al_draw_text(font,
al_map_rgb_f(0.f,
0.
5f,
0.f
),
24,
24,
0, buf
);
243
244 snprintf(buf,
128,
"playback time according to stream: %f", streamTime
);
245 al_draw_text(font,
al_map_rgb_f(0.f,
0.
5f,
0.f
),
24,
40,
0, buf
);
246
247 snprintf(buf,
128,
"total drift: %f", totalDrift
);
248 al_draw_text(font,
al_map_rgb_f(0.f,
0.
5f,
0.f
),
24,
56,
0, buf
);
249
250 snprintf(buf,
128,
"drift per second: %.9f", driftPerSecond
);
251 al_draw_text(font,
al_map_rgb_f(0.f,
0.
5f,
0.f
),
24,
72,
0, buf
);
252
253 snprintf(buf,
128,
"press 'm' to mute, 'n' to unmute, 'r' to reset time elapsed, or 'q' to quit");
254 al_draw_text(font,
al_map_rgb_f(0.f,
0.
5f,
0.f
),
24,
104,
0, buf
);
255
256 al_flip_display();
257 }
258 }
259
260 al_uninstall_audio();
261 al_destroy_display(display
);
262
263 return 0;
264}
]]>
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