[5.0.5] Crash when trying to play the second instance of sound.

no-reply@allegro.cc (Max Savenkov) — Mon, 30 Jan 2012 22:58:30 +0000

I must admit I find Allegro 5 sound interface somewhat confusing. Unlike it's graphic part, it seems somewhat low-level and requires some manual management. And somehow, lacks volume setting for anything, but single sample instance. But maybe I just don't have enough experience with sound APIs. I never tried incorporate sound in my games before. Anyway, I'm trying to write a wrapper for it for my "engine" (it's more of a collection of classes than a real game engine) and I ran into some problems.

Should I be able to attach to one mixer and play two instances of the same ALLEGRO_SAMPLE? When I try to do so, Allegro crashes.

A flattened code for this case looks like this:

#SelectExpand
  1        if ( !al_install_audio() )
  2                return false;
  3
  4        if ( !al_init_acodec_addon() )
  5                return false;
  6
  7        m_pMusicVoice = al_create_voice( 44100, ALLEGRO_AUDIO_DEPTH_INT16, ALLEGRO_CHANNEL_CONF_2 );    
  8        m_pMusicMixer = al_create_mixer( 44100, ALLEGRO_AUDIO_DEPTH_INT16, ALLEGRO_CHANNEL_CONF_2 );
  9        al_attach_mixer_to_voice( m_pMusicMixer, m_pMusicVoice );
 10
 11        ALLEGRO_SAMPLE *m_pSample = al_load_sample( "music.ogg" );
 12
 13        ALLEGRO_SAMPLE_INSTANCE *m_pInstance1 = al_create_sample_instance( m_pSample );
 14        ALLEGRO_SAMPLE_INSTANCE *m_pInstance2 = al_create_sample_instance( m_pSample );
 15
 16        al_attach_sample_instance_to_mixer( m_pInstance1, m_pMusicMixer );
 17        al_attach_sample_instance_to_mixer( m_pInstance2, m_pMusicMixer );
 18
 19        al_play_sample_instance( m_pInstance1 );
 20        _sleep( 500 );
 21        al_play_sample_instance( m_pInstance2 );
 22        _sleep( 10000 );

I expect this to either play music with a 500ms echo or assert somewhere inside Allegro with the message that I can't do this. Instead, I get crash at:

         case ALLEGRO_AUDIO_DEPTH_INT16:
            s[i] = buf->s16[(spl->pos>>MIXER_FRAC_SHIFT)*maxc + i];
            break;

I was unable to quickly determine which part of expression causes crash. s[i] seems valid.

So, the usual question. What am I doing wrong, or is this a bug in Allegro? I'm using monolith build of Allegro 5.0.5 on Windows 7 64-bit.

no-reply@allegro.cc (Matthew Leverton) — Mon, 30 Jan 2012 23:05:15 +0000

Max Savenkov said:

Should I be able to attach to one mixer and play two instances of the same ALLEGRO_SAMPLE?

Yes.

The simpler API, by the way, looks like:

al_install_audio();
al_init_acodec_addon();
al_reserve_samples(n);

spl = al_load_sample(file);
al_play_sample(spl, gain, pan, speed, loop, NULL);

which is really no more difficult than Allegro 4.

no-reply@allegro.cc (Max Savenkov) — Mon, 30 Jan 2012 23:43:55 +0000

Oh, thanks I misunderstood that part of documentation.

EDIT: That does not explain crash, though, so I would still like to get some response on that. Was I using API in the wrong way?

Also, there is a problem with al_play_sample, because you can't do anything with it after it has been started. It seems strange to me. I have SAMPLE_ID. I can stop it. Shouldn't I be able to adjust its gain, at least? Or is there any architectural problems which prevent me from doing this?

EDIT2: OK, I have found what led to crash. I was loading the same file into two different ALLEGRO_SAMPLEs, then creating an INSTANCE of each and trying to play them. While I still don't understand why should this crash library, now at least I can avoid this crash.