sdl_audio.c

MPEG-4编解码的实现(包括MPEG4视音频编解码)

	}
	current_audio = audio;
	if ( current_audio ) {
		current_audio->name = bootstrap[i]->name;
		if ( !current_audio->LockAudio && !current_audio->UnlockAudio ) {
			current_audio->LockAudio = SDL_LockAudio_Default;
			current_audio->UnlockAudio = SDL_UnlockAudio_Default;
		}
	}
	return(0);
}

char *SDL_AudioDriverName(char *namebuf, int maxlen)
{
	if ( current_audio != NULL ) {
		strncpy(namebuf, current_audio->name, maxlen-1);
		namebuf[maxlen-1] = '\0';
		return(namebuf);
	}
	return(NULL);
}

int SDL_OpenAudio(SDL_AudioSpec *desired, SDL_AudioSpec *obtained)
{
	SDL_AudioDevice *audio;

	/* Start up the audio driver, if necessary */
	if ( ! current_audio ) {
		if ( (SDL_InitSubSystem(SDL_INIT_AUDIO) < 0) ||
		     (current_audio == NULL) ) {
			return(-1);
		}
	}
	audio = current_audio;

	if (audio->opened) {
		SDL_SetError("Audio device is already opened");
		return(-1);
	}

	/* Verify some parameters */
	if ( desired->callback == NULL ) {
		SDL_SetError("SDL_OpenAudio() passed a NULL callback");
		return(-1);
	}
	switch ( desired->channels ) {
	    case 1:	/* Mono */
	    case 2:	/* Stereo */
		break;
	    default:
		SDL_SetError("1 (mono) and 2 (stereo) channels supported");
		return(-1);
	}

#ifdef macintosh
	/* FIXME: Need to implement PPC interrupt asm for SDL_LockAudio() */
#else
	/* Create a semaphore for locking the sound buffers */
	audio->mixer_lock = SDL_CreateMutex();
	if ( audio->mixer_lock == NULL ) {
		SDL_SetError("Couldn't create mixer lock");
		SDL_CloseAudio();
		return(-1);
	}
#endif

	/* Calculate the silence and size of the audio specification */
	SDL_CalculateAudioSpec(desired);

	/* Open the audio subsystem */
	memcpy(&audio->spec, desired, sizeof(audio->spec));
	audio->convert.needed = 0;
	audio->enabled = 1;
	audio->paused  = 1;

#ifndef ENABLE_AHI

/* AmigaOS opens audio inside the main loop */
	audio->opened = audio->OpenAudio(audio, &audio->spec)+1;

	if ( ! audio->opened ) {
		SDL_CloseAudio();
		return(-1);
	}
#else
	D(bug("Locking semaphore..."));
	SDL_mutexP(audio->mixer_lock);

	audio->thread = SDL_CreateThread(SDL_RunAudio, audio);
	D(bug("Created thread...\n"));

	if ( audio->thread == NULL ) {
		SDL_mutexV(audio->mixer_lock);
		SDL_CloseAudio();
		SDL_SetError("Couldn't create audio thread");
		return(-1);
	}

	while(!audio_configured)
		SDL_Delay(100);
#endif

	/* If the audio driver changes the buffer size, accept it */
	if ( audio->spec.samples != desired->samples ) {
		desired->samples = audio->spec.samples;
		SDL_CalculateAudioSpec(desired);
	}

	/* Allocate a fake audio memory buffer */
	audio->fake_stream = SDL_AllocAudioMem(audio->spec.size);
	if ( audio->fake_stream == NULL ) {
		SDL_CloseAudio();
		SDL_OutOfMemory();
		return(-1);
	}

	/* See if we need to do any conversion */
	if ( memcmp(desired, &audio->spec, sizeof(audio->spec)) == 0 ) {
		/* Just copy over the desired audio specification */
		if ( obtained != NULL ) {
			memcpy(obtained, &audio->spec, sizeof(audio->spec));
		}
	} else {
		/* Copy over the audio specification if possible */
		if ( obtained != NULL ) {
			memcpy(obtained, &audio->spec, sizeof(audio->spec));
		} else {
			/* Build an audio conversion block */
			if ( SDL_BuildAudioCVT(&audio->convert,
				desired->format, desired->channels,
						desired->freq,
				audio->spec.format, audio->spec.channels,
						audio->spec.freq) < 0 ) {
				SDL_CloseAudio();
				return(-1);
			}
			if ( audio->convert.needed ) {
				audio->convert.len = desired->size;
				audio->convert.buf =(Uint8 *)SDL_AllocAudioMem(
				   audio->convert.len*audio->convert.len_mult);
				if ( audio->convert.buf == NULL ) {
					SDL_CloseAudio();
					SDL_OutOfMemory();
					return(-1);
				}
			}
		}
	}

#ifndef ENABLE_AHI
	/* Start the audio thread if necessary */
	switch (audio->opened) {
		case  1:
			/* Start the audio thread */
			audio->thread = SDL_CreateThread(SDL_RunAudio, audio);
			if ( audio->thread == NULL ) {
				SDL_CloseAudio();
				SDL_SetError("Couldn't create audio thread");
				return(-1);
			}
			break;

		default:
			/* The audio is now playing */
			break;
	}
#else
	SDL_mutexV(audio->mixer_lock);
	D(bug("SDL_OpenAudio USCITA...\n"));

#endif

	return(0);
}

SDL_audiostatus SDL_GetAudioStatus(void)
{
	SDL_AudioDevice *audio = current_audio;
	SDL_audiostatus status;

	status = SDL_AUDIO_STOPPED;
	if ( audio && audio->enabled ) {
		if ( audio->paused ) {
			status = SDL_AUDIO_PAUSED;
		} else {
			status = SDL_AUDIO_PLAYING;
		}
	}
	return(status);
}

void SDL_PauseAudio (int pause_on)
{
	SDL_AudioDevice *audio = current_audio;

	if ( audio ) {
		audio->paused = pause_on;
	}
}

void SDL_LockAudio (void)
{
	SDL_AudioDevice *audio = current_audio;

	/* Obtain a lock on the mixing buffers */
	if ( audio && audio->LockAudio ) {
		audio->LockAudio(audio);
	}
}

void SDL_UnlockAudio (void)
{
	SDL_AudioDevice *audio = current_audio;

	/* Release lock on the mixing buffers */
	if ( audio && audio->UnlockAudio ) {
		audio->UnlockAudio(audio);
	}
}

void SDL_CloseAudio (void)
{
	SDL_QuitSubSystem(SDL_INIT_AUDIO);
}

int SDL_HasAudioDelayMsec (void)
{
  SDL_AudioDevice *audio = current_audio;

  if (audio && audio->AudioDelayMsec != NULL) {
    return 1;
  }
  return 0;
}

int SDL_AudioDelayMsec (void)
{
  SDL_AudioDevice *audio = current_audio;
  if (audio && audio->AudioDelayMsec != NULL) {
    return (audio->AudioDelayMsec(audio));
  } else {
    return (-1);
   }
}


void SDL_AudioQuit(void)
{
	SDL_AudioDevice *audio = current_audio;

	if ( audio ) {
		audio->enabled = 0;
		if ( audio->thread != NULL ) {
			SDL_WaitThread(audio->thread, NULL);
		}
		if ( audio->mixer_lock != NULL ) {
			SDL_DestroyMutex(audio->mixer_lock);
		}
		if ( audio->fake_stream != NULL ) {
			SDL_FreeAudioMem(audio->fake_stream);
		}
		if ( audio->convert.needed ) {
			SDL_FreeAudioMem(audio->convert.buf);

		}
#ifndef ENABLE_AHI
		if ( audio->opened ) {
			audio->CloseAudio(audio);
			audio->opened = 0;
		}
#endif
		/* Free the driver data */
		audio->free(audio);
		current_audio = NULL;
	}
}

#define NUM_FORMATS	6
static int format_idx;
static int format_idx_sub;
static Uint16 format_list[NUM_FORMATS][NUM_FORMATS] = {
 { AUDIO_U8, AUDIO_S8, AUDIO_S16LSB, AUDIO_S16MSB, AUDIO_U16LSB, AUDIO_U16MSB },
 { AUDIO_S8, AUDIO_U8, AUDIO_S16LSB, AUDIO_S16MSB, AUDIO_U16LSB, AUDIO_U16MSB },
 { AUDIO_S16LSB, AUDIO_S16MSB, AUDIO_U16LSB, AUDIO_U16MSB, AUDIO_U8, AUDIO_S8 },
 { AUDIO_S16MSB, AUDIO_S16LSB, AUDIO_U16MSB, AUDIO_U16LSB, AUDIO_U8, AUDIO_S8 },
 { AUDIO_U16LSB, AUDIO_U16MSB, AUDIO_S16LSB, AUDIO_S16MSB, AUDIO_U8, AUDIO_S8 },
 { AUDIO_U16MSB, AUDIO_U16LSB, AUDIO_S16MSB, AUDIO_S16LSB, AUDIO_U8, AUDIO_S8 },
};

Uint16 SDL_FirstAudioFormat(Uint16 format)
{
	for ( format_idx=0; format_idx < NUM_FORMATS; ++format_idx ) {
		if ( format_list[format_idx][0] == format ) {
			break;
		}
	}
	format_idx_sub = 0;
	return(SDL_NextAudioFormat());
}

Uint16 SDL_NextAudioFormat(void)
{
	if ( (format_idx == NUM_FORMATS) || (format_idx_sub == NUM_FORMATS) ) {
		return(0);
	}
	return(format_list[format_idx][format_idx_sub++]);
}

void SDL_CalculateAudioSpec(SDL_AudioSpec *spec)
{
	switch (spec->format) {
		case AUDIO_U8:
			spec->silence = 0x80;
			break;
		default:
			spec->silence = 0x00;
			break;
	}
	spec->size = (spec->format&0xFF)/8;
	spec->size *= spec->channels;
	spec->size *= spec->samples;
}