/*

MIXERLIB: An audio mixer library based on the SDL library

Copyright (C) 1997-1999 Sam Lantinga

This library is free software; you can redistribute it and/or

modify it under the terms of the GNU Library General Public

License as published by the Free Software Foundation; either

version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

Library General Public License for more details.

You should have received a copy of the GNU Library General Public

License along with this library; if not, write to the Free

Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

Sam Lantinga

5635-34 Springhouse Dr.

Pleasanton, CA 94588 (USA)

slouken@devolution.com

*/

/* $Id$ */

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include "SDL_mutex.h"

#include "SDL_endian.h"

#include "SDL_timer.h"

#include "SDL_mixer.h"

static int audio_opened = 0;

static SDL_AudioSpec mixer;

static SDL_mutex *mixer_lock;

static struct _Mix_Channel {

} *mix_channel = NULL;

static int num_channels;

static int reserved_channels = 0;

/* Support for hooking into the mixer callback system */

static void (*mix_postmix)(void *udata, Uint8 *stream, int len) = NULL;

static void *mix_postmix_data = NULL;

/* Music function declarations */

extern int open_music(SDL_AudioSpec *mixer);

extern void close_music(void);

/* Support for user defined music functions, plus the default one */

extern int volatile music_active;

extern void music_mixer(void *udata, Uint8 *stream, int len);

static void (*mix_music)(void *udata, Uint8 *stream, int len) = music_mixer;

static void *music_data = NULL;

/* Mixing function */

static void mix_channels(void *udata, Uint8 *stream, int len)

{

int i, mixable, volume;

Uint32 sdl_ticks;

/* Mix the music (must be done before the channels are added) */

if ( music_active || (mix_music != music_mixer) ) {

mix_music(music_data, stream, len);

}

/* Grab the channels we need to mix */

SDL_mutexP(mixer_lock);

sdl_ticks = SDL_GetTicks();

for ( i=0; i<num_channels; ++i ) {

if( ! mix_channel[i].paused ) {

if ( mix_channel[i].expire > 0 && mix_channel[i].expire < sdl_ticks ) {

/* Expiration delay for that channel is reached */

mix_channel[i].playing = 0;

mix_channel[i].fading = MIX_NO_FADING;

mix_channel[i].expire = 0;

} else if ( mix_channel[i].fading != MIX_NO_FADING ) {

Uint32 ticks = sdl_ticks - mix_channel[i].ticks_fade;

if( ticks > mix_channel[i].fade_length ) {

if( mix_channel[i].fading == MIX_FADING_OUT ) {

mix_channel[i].playing = 0;

mix_channel[i].expire = 0;

Mix_Volume(i, mix_channel[i].fading); /* Restore the volume */

}

mix_channel[i].fading = MIX_NO_FADING;

} else {

if( mix_channel[i].fading == MIX_FADING_OUT ) {

Mix_Volume(i, (mix_channel[i].fade_volume * (mix_channel[i].fade_length-ticks))

/ mix_channel[i].fade_length );

} else {

Mix_Volume(i, (mix_channel[i].fade_volume * ticks) / mix_channel[i].fade_length );

}

}

}

if ( mix_channel[i].playing > 0 ) {

volume = (mix_channel[i].volume*mix_channel[i].chunk->volume) / MIX_MAX_VOLUME;

mixable = mix_channel[i].playing;

if ( mixable > len ) {

mixable = len;

}

SDL_MixAudio(stream,mix_channel[i].samples,mixable,volume);

mix_channel[i].samples += mixable;

mix_channel[i].playing -= mixable;

/* If looping the sample and we are at its end, make sure

we will still return a full buffer */

while ( mix_channel[i].looping && mixable < len ) {

int remaining = len - mixable;

int alen = mix_channel[i].chunk->alen;

if (remaining > alen) {

remaining = alen;

}

SDL_MixAudio(stream+mixable, mix_channel[i].chunk->abuf, remaining, volume);

--mix_channel[i].looping;

mix_channel[i].samples = mix_channel[i].chunk->abuf + remaining;

mix_channel[i].playing = mix_channel[i].chunk->alen - remaining;

mixable += remaining;

}

if ( ! mix_channel[i].playing && mix_channel[i].looping ) {

if ( --mix_channel[i].looping ) {

mix_channel[i].samples = mix_channel[i].chunk->abuf;

mix_channel[i].playing = mix_channel[i].chunk->alen;

}

}

}

}

}

if ( mix_postmix ) {

mix_postmix(mix_postmix_data, stream, len);

}

SDL_mutexV(mixer_lock);

}

static void PrintFormat(char *title, SDL_AudioSpec *fmt)

{

printf("%s: %d bit %s audio (%s) at %u Hz\n", title, (fmt->format&0xFF),

(fmt->format&0x8000) ? "signed" : "unsigned",

(fmt->channels > 1) ? "stereo" : "mono", fmt->freq);

}

/* Open the mixer with a certain desired audio format */

int Mix_OpenAudio(int frequency, Uint16 format, int nchannels, int chunksize)

{

int i;

SDL_AudioSpec desired;

/* If the mixer is already opened, increment open count */

if ( audio_opened ) {

++audio_opened;

return(0);

}

/* Set the desired format and frequency */

desired.freq = frequency;

desired.format = format;

desired.channels = nchannels;

desired.samples = chunksize;

desired.callback = mix_channels;

desired.userdata = NULL;

/* Accept nearly any audio format */

if ( SDL_OpenAudio(&desired, &mixer) < 0 ) {

return(-1);

}

#if 0

PrintFormat("Audio device", &mixer);

#endif

/* Create the channel lock mutex */

mixer_lock = SDL_CreateMutex();

#ifndef macintosh /* Hmm.. what implications does this have? */

if ( mixer_lock == NULL ) {

SDL_CloseAudio();

SDL_SetError("Unable to create mixer lock");

return(-1);

}

#endif

/* Initialize the music players */

if ( open_music(&mixer) < 0 ) {

SDL_CloseAudio();

SDL_DestroyMutex(mixer_lock);

return(-1);

}

num_channels = MIX_CHANNELS;

mix_channel = (struct _Mix_Channel *) malloc(num_channels * sizeof(struct _Mix_Channel));

/* Clear out the audio channels */

for ( i=0; i<num_channels; ++i ) {

mix_channel[i].chunk = NULL;

mix_channel[i].playing = 0;

mix_channel[i].looping = 0;

mix_channel[i].volume = SDL_MIX_MAXVOLUME;

mix_channel[i].tag = -1;

mix_channel[i].expire = 0;

}

Mix_VolumeMusic(SDL_MIX_MAXVOLUME);

audio_opened = 1;

SDL_PauseAudio(0);

return(0);

}

/* Dynamically change the number of channels managed by the mixer.

If decreasing the number of channels, the upper channels are

stopped.

*/

int Mix_AllocateChannels(int numchans)

{

if ( numchans<0 || numchans==num_channels )

return(num_channels);

if ( numchans < num_channels ) {

/* Stop the affected channels */

int i;

for(i=numchans; i < num_channels; i++) {

Mix_HaltChannel(i);

}

}

SDL_mutexP(mixer_lock);

mix_channel = (struct _Mix_Channel *) realloc(mix_channel, numchans * sizeof(struct _Mix_Channel));

if ( numchans > num_channels ) {

/* Initialize the new channels */

int i;

for(i=num_channels; i < numchans; i++) {

mix_channel[i].chunk = NULL;

mix_channel[i].playing = 0;

mix_channel[i].looping = 0;

mix_channel[i].volume = SDL_MIX_MAXVOLUME;

mix_channel[i].tag = -1;

mix_channel[i].expire = 0;

}

}

num_channels = numchans;

SDL_mutexV(mixer_lock);

return(num_channels);

}

/* Return the actual mixer parameters */

int Mix_QuerySpec(int *frequency, Uint16 *format, int *channels)

{

if ( audio_opened ) {

if ( frequency ) {

*frequency = mixer.freq;

}

if ( format ) {

*format = mixer.format;

}

if ( channels ) {

*channels = mixer.channels;

}

}

return(audio_opened);

}

/*

* !!! FIXME: Ideally, we want a Mix_LoadSample_RW(), which will handle the

* generic setup, then call the correct file format loader.

*/

#ifdef VOC_SAMPLES

SDL_AudioSpec *Mix_LoadVOC_RW (SDL_RWops *src, int freesrc,

SDL_AudioSpec *spec, Uint8 **audio_buf, Uint32 *audio_len);

#endif

/* Load a wave file */

Mix_Chunk *Mix_LoadWAV_RW(SDL_RWops *src, int freesrc)

{

Mix_Chunk *chunk;

SDL_AudioSpec wavespec;

SDL_AudioCVT wavecvt;

int samplesize;

/* rcg06012001 Make sure src is valid */

if ( ! src ) {

SDL_SetError("Mix_LoadWAV_RW with NULL SDL_RWops");

return(NULL);

}

/* Make sure audio has been opened */

if ( ! audio_opened ) {

SDL_SetError("Audio device hasn't been opened");

if ( freesrc && src ) {

SDL_RWclose(src);

}

return(NULL);

}

/* Allocate the chunk memory */

chunk = (Mix_Chunk *)malloc(sizeof(Mix_Chunk));

if ( chunk == NULL ) {

SDL_SetError("Out of memory");

if ( freesrc ) {

SDL_RWclose(src);

}

return(NULL);

}

/* rcg06012001 Handle Creative Labs .VOC format chunks. */

#ifdef VOC_SAMPLES

if ( Mix_LoadVOC_RW(src, 0,

&wavespec, (Uint8 **)&chunk->abuf, &chunk->alen) == NULL ) {

#endif

/* Load the WAV file into the chunk */

if ( SDL_LoadWAV_RW(src, freesrc,

&wavespec, (Uint8 **)&chunk->abuf, &chunk->alen) == NULL ) {

free(chunk);

return(NULL);

}

#ifdef VOC_SAMPLES

}

#endif

#if 0

PrintFormat("Audio device", &mixer);

PrintFormat("-- Wave file", &wavespec);

#endif

/* Build the audio converter and create conversion buffers */

if ( SDL_BuildAudioCVT(&wavecvt,

wavespec.format, wavespec.channels, wavespec.freq,

mixer.format, mixer.channels, mixer.freq) < 0 ) {

SDL_FreeWAV(chunk->abuf);

free(chunk);

return(NULL);

}

samplesize = ((wavespec.format & 0xFF)/8)*wavespec.channels;

wavecvt.len = chunk->alen & ~(samplesize-1);

wavecvt.buf = (Uint8 *)malloc(wavecvt.len*wavecvt.len_mult);

if ( wavecvt.buf == NULL ) {

SDL_SetError("Out of memory");

SDL_FreeWAV(chunk->abuf);

free(chunk);

return(NULL);

}

memcpy(wavecvt.buf, chunk->abuf, chunk->alen);

SDL_FreeWAV(chunk->abuf);

/* Run the audio converter */

if ( SDL_ConvertAudio(&wavecvt) < 0 ) {

free(wavecvt.buf);

free(chunk);

return(NULL);

}

chunk->allocated = 1;

chunk->abuf = wavecvt.buf;

chunk->alen = wavecvt.len_cvt;

chunk->volume = MIX_MAX_VOLUME;

return(chunk);

}

/* Load a wave file of the mixer format from a memory buffer */

Mix_Chunk *Mix_QuickLoad_WAV(Uint8 *mem)

{

Mix_Chunk *chunk;

Uint8 magic[4];

/* Make sure audio has been opened */

if ( ! audio_opened ) {

SDL_SetError("Audio device hasn't been opened");

return(NULL);

}

/* Allocate the chunk memory */

chunk = (Mix_Chunk *)malloc(sizeof(Mix_Chunk));

if ( chunk == NULL ) {

SDL_SetError("Out of memory");

return(NULL);

}

/* Essentially just skip to the audio data (no error checking - fast) */

chunk->allocated = 0;

mem += 12; /* WAV header */

do {

memcpy(magic, mem, 4);

mem += 4;

chunk->alen = ((mem[3]<<24)|(mem[2]<<16)|(mem[1]<<8)|(mem[0]));

mem += 4;

chunk->abuf = mem;

mem += chunk->alen;

} while ( memcmp(magic, "data", 4) != 0 );

chunk->volume = MIX_MAX_VOLUME;

return(chunk);

}

/* Free an audio chunk previously loaded */

void Mix_FreeChunk(Mix_Chunk *chunk)

{

int i;

/* Caution -- if the chunk is playing, the mixer will crash */

if ( chunk ) {

/* Guarantee that this chunk isn't playing */

if ( mix_channel ) {

SDL_mutexP(mixer_lock);

for ( i=0; i<num_channels; ++i ) {

if ( chunk == mix_channel[i].chunk ) {

mix_channel[i].playing = 0;

}

}

SDL_mutexV(mixer_lock);

}

/* Actually free the chunk */

if ( chunk->allocated ) {

free(chunk->abuf);

}

free(chunk);

}

}

/* Set a function that is called after all mixing is performed.

This can be used to provide real-time visual display of the audio stream

or add a custom mixer filter for the stream data.

*/

void Mix_SetPostMix(void (*mix_func)

(void *udata, Uint8 *stream, int len), void *arg)

{

SDL_LockAudio();

mix_postmix_data = arg;

mix_postmix = mix_func;

SDL_UnlockAudio();

}

/* Add your own music player or mixer function.

If 'mix_func' is NULL, the default music player is re-enabled.

*/

void Mix_HookMusic(void (*mix_func)(void *udata, Uint8 *stream, int len),

void *arg)

{

SDL_LockAudio();

if ( mix_func != NULL ) {

music_data = arg;

mix_music = mix_func;

} else {

music_data = NULL;

mix_music = music_mixer;

}

SDL_UnlockAudio();

}

void *Mix_GetMusicHookData(void)

{

return(music_data);

}

/* Reserve the first channels (0 -> n-1) for the application, i.e. don't allocate

them dynamically to the next sample if requested with a -1 value below.

Returns the number of reserved channels.

*/

int Mix_ReserveChannels(int num)

{

if (num > num_channels)

num = num_channels;

reserved_channels = num;

return num;

}

/* Play an audio chunk on a specific channel.

If the specified channel is -1, play on the first free channel.

'ticks' is the number of milliseconds at most to play the sample, or -1

if there is no limit.

Returns which channel was used to play the sound.

*/

int Mix_PlayChannelTimed(int which, Mix_Chunk *chunk, int loops, int ticks)

{

int i;

/* Don't play null pointers :-) */

if ( chunk == NULL ) {

return(-1);

}

/* Lock the mixer while modifying the playing channels */

SDL_mutexP(mixer_lock);

{

/* If which is -1, play on the first free channel */

if ( which == -1 ) {

for ( i=reserved_channels; i<num_channels; ++i ) {

if ( mix_channel[i].playing <= 0 )

break;

}

if ( i == num_channels ) {

which = -1;

} else {

which = i;

}

}

/* Queue up the audio data for this channel */

if ( which >= 0 ) {

Uint32 sdl_ticks = SDL_GetTicks();

mix_channel[which].samples = chunk->abuf;

mix_channel[which].playing = chunk->alen;

mix_channel[which].looping = loops;

mix_channel[which].chunk = chunk;

mix_channel[which].paused = 0;

mix_channel[which].fading = MIX_NO_FADING;

mix_channel[which].start_time = sdl_ticks;

mix_channel[which].expire = (ticks>0) ? (sdl_ticks + ticks) : 0;

}

}

SDL_mutexV(mixer_lock);

/* Return the channel on which the sound is being played */

return(which);

}

/* Change the expiration delay for a channel */

int Mix_ExpireChannel(int which, int ticks)

{

int status = 0;

if ( which == -1 ) {

int i;

for ( i=0; i < num_channels; ++ i ) {

status += Mix_ExpireChannel(i, ticks);

}

} else if ( which < num_channels ) {

SDL_mutexP(mixer_lock);

mix_channel[which].expire = (ticks>0) ? (SDL_GetTicks() + ticks) : 0;

SDL_mutexV(mixer_lock);

++ status;

}

return(status);

}

/* Fade in a sound on a channel, over ms milliseconds */

int Mix_FadeInChannelTimed(int which, Mix_Chunk *chunk, int loops, int ms, int ticks)

{

int i;

/* Don't play null pointers :-) */

if ( chunk == NULL ) {

return(-1);

}

/* Lock the mixer while modifying the playing channels */

SDL_mutexP(mixer_lock);

{

/* If which is -1, play on the first free channel */

if ( which == -1 ) {

for ( i=reserved_channels; i<num_channels; ++i ) {

if ( mix_channel[i].playing <= 0 )

break;

}

if ( i == num_channels ) {

which = -1;

} else {

which = i;

}

}

/* Queue up the audio data for this channel */

if ( which >= 0 ) {

Uint32 sdl_ticks = SDL_GetTicks();

mix_channel[which].samples = chunk->abuf;

mix_channel[which].playing = chunk->alen;

mix_channel[which].looping = loops;

mix_channel[which].chunk = chunk;

mix_channel[which].paused = 0;

mix_channel[which].fading = MIX_FADING_IN;

mix_channel[which].fade_volume = mix_channel[which].volume;

mix_channel[which].volume = 0;

mix_channel[which].fade_length = (Uint32)ms;

mix_channel[which].start_time = mix_channel[which].ticks_fade = sdl_ticks;

mix_channel[which].expire = (ticks > 0) ? (sdl_ticks+ticks) : 0;

}

}

SDL_mutexV(mixer_lock);

/* Return the channel on which the sound is being played */

return(which);

}

/* Set volume of a particular channel */

int Mix_Volume(int which, int volume)

{

int i;

int prev_volume;

if ( which == -1 ) {

prev_volume = 0;

for ( i=0; i<num_channels; ++i ) {

prev_volume += Mix_Volume(i, volume);

}

prev_volume /= num_channels;

} else {

prev_volume = mix_channel[which].volume;

if ( volume < 0 ) {

volume = 0;

}

if ( volume > SDL_MIX_MAXVOLUME ) {

volume = SDL_MIX_MAXVOLUME;

}

mix_channel[which].volume = volume;

}

return(prev_volume);

}

/* Set volume of a particular chunk */

int Mix_VolumeChunk(Mix_Chunk *chunk, int volume)

{

int prev_volume;

prev_volume = chunk->volume;

if ( volume >= 0 ) {

if ( volume > MIX_MAX_VOLUME ) {

volume = MIX_MAX_VOLUME;

}

chunk->volume = volume;

}

return(prev_volume);

}

/* Halt playing of a particular channel */

int Mix_HaltChannel(int which)

{

int i;

if ( which == -1 ) {

for ( i=0; i<num_channels; ++i ) {

Mix_HaltChannel(i);

}

} else {

SDL_mutexP(mixer_lock);

mix_channel[which].playing = 0;

mix_channel[which].expire = 0;

if(mix_channel[which].fading != MIX_NO_FADING) /* Restore volume */

mix_channel[which].volume = mix_channel[which].fade_volume;

mix_channel[which].fading = MIX_NO_FADING;

SDL_mutexV(mixer_lock);

}

return(0);

}

/* Halt playing of a particular group of channels */

int Mix_HaltGroup(int tag)

{

int i;

for ( i=0; i<num_channels; ++i ) {

if( mix_channel[i].tag == tag ) {

Mix_HaltChannel(i);

}

}

return(0);

}

/* Fade out a channel and then stop it automatically */

int Mix_FadeOutChannel(int which, int ms)

{

int status;

status = 0;

if ( audio_opened ) {

if ( which == -1 ) {

int i;

for ( i=0; i<num_channels; ++i ) {

status += Mix_FadeOutChannel(i, ms);

}

} else {

SDL_mutexP(mixer_lock);

if ( mix_channel[which].playing &&

(mix_channel[which].volume > 0) &&

(mix_channel[which].fading != MIX_FADING_OUT) ) {

mix_channel[which].fading = MIX_FADING_OUT;

mix_channel[which].fade_volume = mix_channel[which].volume;

mix_channel[which].fade_length = ms;

mix_channel[which].ticks_fade = SDL_GetTicks();

++status;

}

SDL_mutexV(mixer_lock);

}

}

return(status);

}

/* Halt playing of a particular group of channels */

int Mix_FadeOutGroup(int tag, int ms)

{

int i;

int status = 0;

for ( i=0; i<num_channels; ++i ) {

if( mix_channel[i].tag == tag ) {

status += Mix_FadeOutChannel(i,ms);

}

}

return(status);

}

Mix_Fading Mix_FadingChannel(int which)

{

return mix_channel[which].fading;

}

/* Check the status of a specific channel.

If the specified mix_channel is -1, check all mix_channels.

*/

int Mix_Playing(int which)

{

int status;

status = 0;

if ( which == -1 ) {

int i;

for ( i=0; i<num_channels; ++i ) {

if ( mix_channel[i].playing > 0 ) {

++status;

}

}

} else {

if ( mix_channel[which].playing > 0 ) {

++status;

}

}

return(status);

}

/* Close the mixer, halting all playing audio */

void Mix_CloseAudio(void)

{

if ( audio_opened ) {

if ( audio_opened == 1 ) {

close_music();

Mix_HaltChannel(-1);

SDL_CloseAudio();

SDL_DestroyMutex(mixer_lock);

free(mix_channel);

mix_channel = NULL;

}

--audio_opened;

}

}

/* Pause a particular channel (or all) */

void Mix_Pause(int which)

{

Uint32 sdl_ticks = SDL_GetTicks();

if ( which == -1 ) {

int i;

for ( i=0; i<num_channels; ++i ) {

if ( mix_channel[i].playing > 0 ) {

mix_channel[i].paused = sdl_ticks;

}

}

} else {

if ( mix_channel[which].playing > 0 ) {

mix_channel[which].paused = sdl_ticks;

}

}

}

/* Resume a paused channel */

void Mix_Resume(int which)

{

Uint32 sdl_ticks = SDL_GetTicks();

if ( which == -1 ) {

int i;

SDL_mutexP(mixer_lock);

for ( i=0; i<num_channels; ++i ) {

if ( mix_channel[i].playing > 0 ) {

if(mix_channel[i].expire > 0)

mix_channel[i].expire += sdl_ticks - mix_channel[i].paused;

mix_channel[i].paused = 0;

}

}

SDL_mutexV(mixer_lock);

} else {

SDL_mutexP(mixer_lock);

if ( mix_channel[which].playing > 0 ) {

if(mix_channel[which].expire > 0)

mix_channel[which].expire += sdl_ticks - mix_channel[which].paused;

mix_channel[which].paused = 0;

}

SDL_mutexV(mixer_lock);

}

}

int Mix_Paused(int which)

{

if ( which > num_channels )

return(0);

if ( which < 0 ) {

int status = 0;

int i;

for( i=0; i < num_channels; ++i ) {

if ( mix_channel[i].paused ) {

++ status;

}

}

return(status);

} else {

return(mix_channel[which].paused != 0);

}

}

/* Change the group of a channel */

int Mix_GroupChannel(int which, int tag)

{

if ( which < 0 || which > num_channels )

return(0);

SDL_mutexP(mixer_lock);

mix_channel[which].tag = tag;

SDL_mutexV(mixer_lock);

return(1);

}

/* Assign several consecutive channels to a group */

int Mix_GroupChannels(int from, int to, int tag)

{

int status = 0;

for( ; from <= to; ++ from ) {

status += Mix_GroupChannel(from, tag);

}

return(status);

}

/* Finds the first available channel in a group of channels */

int Mix_GroupAvailable(int tag)

{

int i;

for( i=0; i < num_channels; i ++ ) {

if ( ((tag == -1) || (tag == mix_channel[i].tag)) &&

(mix_channel[i].playing <= 0) )

return i;

}

return(-1);

}

int Mix_GroupCount(int tag)

{

int count = 0;

int i;

for( i=0; i < num_channels; i ++ ) {

if ( mix_channel[i].tag==tag || tag==-1 )

++ count;

}

return(count);

}

/* Finds the "oldest" sample playing in a group of channels */

int Mix_GroupOldest(int tag)

{

int chan = -1;

Uint32 mintime = SDL_GetTicks();

int i;

for( i=0; i < num_channels; i ++ ) {

if ( (mix_channel[i].tag==tag || tag==-1) && mix_channel[i].playing > 0

&& mix_channel[i].start_time <= mintime ) {

mintime = mix_channel[i].start_time;

chan = i;

}

}

return(chan);

}

/* Finds the "most recent" (i.e. last) sample playing in a group of channels */

int Mix_GroupNewer(int tag)

{

int chan = -1;

Uint32 maxtime = 0;

int i;

for( i=0; i < num_channels; i ++ ) {

if ( (mix_channel[i].tag==tag || tag==-1) && mix_channel[i].playing > 0

&& mix_channel[i].start_time >= maxtime ) {

maxtime = mix_channel[i].start_time;

chan = i;

}

}

return(chan);

}