SDL_mixer: An audio mixer library based on the SDL library

Copyright (C) 1997-2012 Sam Lantinga <slouken@libsdl.org>

This software is provided 'as-is', without any express or implied

warranty. In no event will the authors be held liable for any damages

arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,

including commercial applications, and to alter it and redistribute it

freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not

claim that you wrote the original software. If you use this software

in a product, an acknowledgment in the product documentation would be

appreciated but is not required.

2. Altered source versions must be plainly marked as such, and must not be

misrepresented as being the original software.

3. This notice may not be removed or altered from any source distribution.

*/

#ifdef MP3_MAD_MUSIC

#include <string.h>

#include "music_mad.h"

static int

MAD_RWread(mad_data *music, void *ptr, int size, int maxnum) {

int remaining = music->length - music->pos;

int ret;

maxnum *= size;

if (maxnum > remaining) maxnum = remaining;

ret = SDL_RWread(music->rw, ptr, 1, maxnum);

if (ret > 0) music->pos += ret;

return ret;

}

static int

MAD_RWseek(mad_data *music, int offset, int whence) {

int ret;

switch (whence) { /* assumes a legal whence value */

case RW_SEEK_CUR:

offset += music->pos;

break;

case RW_SEEK_END:

offset = music->length + offset;

break;

}

if (offset < 0) return -1;

if (offset > music->length)

offset = music->length;

ret = SDL_RWseek(music->rw, music->start + offset, RW_SEEK_SET);

if (ret < 0) return ret;

music->pos = offset;

return (music->pos - music->start);

}

/* SDL-1.2 doesn't have a SDL_RWsize() */

static int SDL12_RWsize(SDL_RWops *rw) {

int pos, size;

if ((pos=SDL_RWtell(rw))<0) return -1;

size = SDL_RWseek(rw, 0, RW_SEEK_END);

SDL_RWseek(rw, pos, RW_SEEK_SET);

return size;

}

static int skip_tags (mad_data *);

mad_openFileRW(SDL_RWops *rw, SDL_AudioSpec *mixer, int freerw)

{

mad_data *mp3_mad;

if (mp3_mad) {

mp3_mad->rw = rw;

mp3_mad->start = 0;

mp3_mad->pos = 0;

mp3_mad->length = SDL12_RWsize(rw);

if (skip_tags(mp3_mad) < 0) {

SDL_free(mp3_mad);

Mix_SetError("music_mad: corrupt mp3 file.");

return NULL;

}

mad_stream_init(&mp3_mad->stream);

mad_frame_init(&mp3_mad->frame);

mad_synth_init(&mp3_mad->synth);

mp3_mad->frames_read = 0;

mad_timer_reset(&mp3_mad->next_frame_start);

mp3_mad->volume = MIX_MAX_VOLUME;

mp3_mad->status = 0;

mp3_mad->output_begin = 0;

mp3_mad->output_end = 0;

mp3_mad->mixer = *mixer;

}

return mp3_mad;

}

void

mad_closeFile(mad_data *mp3_mad)

{

mad_stream_finish(&mp3_mad->stream);

mad_frame_finish(&mp3_mad->frame);

mad_synth_finish(&mp3_mad->synth);

}

/* Starts the playback. */

void

mad_start(mad_data *mp3_mad) {

mp3_mad->status |= MS_playing;

}

/* Stops the playback. */

void

mad_stop(mad_data *mp3_mad) {

mp3_mad->status &= ~MS_playing;

}

/* Returns true if the playing is engaged, false otherwise. */

int

mad_isPlaying(mad_data *mp3_mad) {

return ((mp3_mad->status & MS_playing) != 0);

}

/*************************** TAG HANDLING: ******************************/

{

/* http://id3.org/ID3v1 : 3 bytes "TAG" identifier and 125 bytes tag data */

if (length < 3 || SDL_memcmp(data,"TAG",3) != 0) {

return SDL_FALSE;

}

return SDL_TRUE;

}

static __inline__ SDL_bool is_id3v1ext(const unsigned char *data, int length)

{

/* ID3v1 extended tag: just before ID3v1, always 227 bytes.

* https://www.getid3.org/phpBB3/viewtopic.php?t=1202

* https://en.wikipedia.org/wiki/ID3v1#Enhanced_tag

* Not an official standard, is only supported by few programs. */

if (length < 4 || SDL_memcmp(data,"TAG+",4) != 0) {

return SDL_FALSE;

}

return SDL_TRUE;

}

static __inline__ SDL_bool is_id3v2(const unsigned char *data, int length)

{

/* ID3v2 header is 10 bytes: http://id3.org/id3v2.4.0-structure */

/* bytes 0-2: "ID3" identifier */

if (length < 10 || SDL_memcmp(data,"ID3",3) != 0) {

return SDL_FALSE;

}

/* bytes 3-4: version num (major,revision), each byte always less than 0xff. */

if (data[3] == 0xff || data[4] == 0xff) {

return SDL_FALSE;

}

/* bytes 6-9 are the ID3v2 tag size: a 32 bit 'synchsafe' integer, i.e. the

* highest bit 7 in each byte zeroed. i.e.: 7 bit information in each byte ->

* effectively a 28 bit value. */

if (data[6] >= 0x80 || data[7] >= 0x80 || data[8] >= 0x80 || data[9] >= 0x80) {

return SDL_FALSE;

}

return SDL_TRUE;

}

static __inline__ int get_id3v2_len(const unsigned char *data, long length)

{

/* size is a 'synchsafe' integer (see above) */

int size = (int)((data[6]<<21) + (data[7]<<14) + (data[8]<<7) + data[9]);

size += 10; /* header size */

/* ID3v2 header[5] is flags (bits 4-7 only, 0-3 are zero).

* bit 4 set: footer is present (a copy of the header but

* with "3DI" as ident.) */

if (data[5] & 0x10) {

size += 10; /* footer size */

}

/* optional padding (always zeroes) */

while (size < length && data[size] == 0) {

++size;

}

return size;

}

static __inline__ SDL_bool is_apetag(const unsigned char *data, int length)

{

/* http://wiki.hydrogenaud.io/index.php?title=APEv2_specification

* Header/footer is 32 bytes: bytes 0-7 ident, bytes 8-11 version,

* bytes 12-17 size. bytes 24-31 are reserved: must be all zeroes. */

Uint32 v;

if (length < 32 || SDL_memcmp(data,"APETAGEX",8) != 0) {

return SDL_FALSE;

}

v = (data[11]<<24) | (data[10]<<16) | (data[9]<<8) | data[8]; /* version */

return SDL_FALSE;

}

v = 0; /* reserved bits : */

if (SDL_memcmp(&data[24],&v,4) != 0 || SDL_memcmp(&data[28],&v,4) != 0) {

return SDL_FALSE;

}

return SDL_TRUE;

}

int size = (int)((data[15]<<24) | (data[14]<<16) | (data[13]<<8) | data[12]);

*version = (data[11]<<24) | (data[10]<<16) | (data[9]<<8) | data[8];

return size; /* caller will handle the additional v2 header length */

}

static int skip_tags(mad_data *music)

{

int len, readsize;

readsize = MAD_RWread(music, music->input_buffer, 1, MAD_INPUT_BUFFER_SIZE);

if (readsize <= 0) return -1;

/* ID3v2 tag is at the start */

if (is_id3v2(music->input_buffer, readsize)) {

len = get_id3v2_len(music->input_buffer, readsize);

if (len >= music->length) return -1;

music->start += len;

music->length -= len;

MAD_RWseek(music, 0, RW_SEEK_SET);

}

/* APE tag _might_ be at the start: read the header */

else if (is_apetag(music->input_buffer, readsize)) {

Uint32 v;

len = get_ape_len(music->input_buffer, readsize, &v);

len += 32; /* we're at top: have a header. */

if (len >= music->length) return -1;

music->start += len;

music->length -= len;

MAD_RWseek(music, 0, RW_SEEK_SET);

/* ID3v1 tag is at the end */

if (music->length < 128) goto ape;

MAD_RWseek(music, -128, RW_SEEK_END);

readsize = MAD_RWread(music, music->input_buffer, 1, 128);

MAD_RWseek(music, 0, RW_SEEK_SET);

if (readsize != 128) return -1;

if (is_id3v1(music->input_buffer, 128)) {

music->length -= 128;

/* APE tag may be before the ID3v1: read the footer */

if (music->length < 32) goto end;

MAD_RWseek(music, -32, RW_SEEK_END);

readsize = MAD_RWread(music, music->input_buffer, 1, 32);

MAD_RWseek(music, 0, RW_SEEK_SET);

if (readsize != 32) return -1;

if (is_apetag(music->input_buffer, 32)) {

Uint32 v;

len = get_ape_len(music->input_buffer, readsize, &v);

if (v == 2000U) len += 32; /* header */

if (len >= music->length) return -1;

if (v == 2000U) { /* verify header : */

MAD_RWseek(music, -len, RW_SEEK_END);

readsize = MAD_RWread(music, music->input_buffer, 1, 32);

MAD_RWseek(music, 0, RW_SEEK_SET);

if (readsize != 32) return -1;

if (!is_apetag(music->input_buffer, 32)) return -1;

}

music->length -= len;

goto end;

/* extended ID3v1 just before the ID3v1 tag? (unlikely) */

if (music->length < 227) goto end;

MAD_RWseek(music, -227, RW_SEEK_END);

readsize = MAD_RWread(music, music->input_buffer, 1, 227);

MAD_RWseek(music, 0, RW_SEEK_SET);

if (readsize != 227) return -1;

if (is_id3v1ext(music->input_buffer, 227)) {

music->length -= 227;

goto end;

}

}

ape: /* APE tag may be at the end: read the footer */

if (music->length >= 32) {

MAD_RWseek(music, -32, RW_SEEK_END);

readsize = MAD_RWread(music, music->input_buffer, 1, 32);

MAD_RWseek(music, 0, RW_SEEK_SET);

if (readsize != 32) return -1;

if (is_apetag(music->input_buffer, 32)) {

Uint32 v;

len = get_ape_len(music->input_buffer, readsize, &v);

if (v == 2000U) len += 32; /* header */

if (len >= music->length) return -1;

if (v == 2000U) { /* verify header : */

MAD_RWseek(music, -len, RW_SEEK_END);

readsize = MAD_RWread(music, music->input_buffer, 1, 32);

MAD_RWseek(music, 0, RW_SEEK_SET);

if (readsize != 32) return -1;

if (!is_apetag(music->input_buffer, 32)) return -1;

}

music->length -= len;

}

}

end:

return (music->length > 0)? 0: -1;

}

/* Reads the next frame from the file. Returns true on success or

false on failure. */

static int

read_next_frame(mad_data *mp3_mad) {

if (mp3_mad->stream.buffer == NULL ||

mp3_mad->stream.error == MAD_ERROR_BUFLEN) {

size_t read_size;

size_t remaining;

unsigned char *read_start;

/* There might be some bytes in the buffer left over from last

time. If so, move them down and read more bytes following

them. */

if (mp3_mad->stream.next_frame != NULL) {

remaining = mp3_mad->stream.bufend - mp3_mad->stream.next_frame;

memmove(mp3_mad->input_buffer, mp3_mad->stream.next_frame, remaining);

read_start = mp3_mad->input_buffer + remaining;

read_size = MAD_INPUT_BUFFER_SIZE - remaining;

} else {

read_size = MAD_INPUT_BUFFER_SIZE;

read_start = mp3_mad->input_buffer;

remaining = 0;

}

/* Now read additional bytes from the input file. */

if (read_size <= 0) {

if ((mp3_mad->status & (MS_input_eof | MS_input_error)) == 0) {

if (read_size == 0) {

mp3_mad->status |= MS_input_eof;

} else {

mp3_mad->status |= MS_input_error;

}

/* At the end of the file, we must stuff MAD_BUFFER_GUARD

number of 0 bytes. */

memset(read_start + read_size, 0, MAD_BUFFER_GUARD);

read_size += MAD_BUFFER_GUARD;

}

}

/* Now feed those bytes into the libmad stream. */

mad_stream_buffer(&mp3_mad->stream, mp3_mad->input_buffer,

read_size + remaining);

mp3_mad->stream.error = MAD_ERROR_NONE;

}

/* Now ask libmad to extract a frame from the data we just put in

its buffer. */

if (mad_frame_decode(&mp3_mad->frame, &mp3_mad->stream)) {

if (MAD_RECOVERABLE(mp3_mad->stream.error)) {

return 0;

} else if (mp3_mad->stream.error == MAD_ERROR_BUFLEN) {

return 0;

} else {

mp3_mad->status |= MS_decode_error;

return 0;

}

}

mp3_mad->frames_read++;

mad_timer_add(&mp3_mad->next_frame_start, mp3_mad->frame.header.duration);

return 1;

}

/* Scale a MAD sample to 16 bits for output. */

static signed int

scale(mad_fixed_t sample) {

/* round */

sample += (1L << (MAD_F_FRACBITS - 16));

/* clip */

if (sample >= MAD_F_ONE)

sample = MAD_F_ONE - 1;

else if (sample < -MAD_F_ONE)

sample = -MAD_F_ONE;

/* quantize */

return sample >> (MAD_F_FRACBITS + 1 - 16);

}

/* Once the frame has been read, copies its samples into the output

buffer. */

static void

decode_frame(mad_data *mp3_mad) {

struct mad_pcm *pcm;

unsigned int nchannels, nsamples;

mad_fixed_t const *left_ch, *right_ch;

unsigned char *out;

int ret;

mad_synth_frame(&mp3_mad->synth, &mp3_mad->frame);

pcm = &mp3_mad->synth.pcm;

out = mp3_mad->output_buffer + mp3_mad->output_end;

if ((mp3_mad->status & MS_cvt_decoded) == 0) {

mp3_mad->status |= MS_cvt_decoded;

/* The first frame determines some key properties of the stream.

In particular, it tells us enough to set up the convert

structure now. */

SDL_BuildAudioCVT(&mp3_mad->cvt, AUDIO_S16, pcm->channels, mp3_mad->frame.header.samplerate, mp3_mad->mixer.format, mp3_mad->mixer.channels, mp3_mad->mixer.freq);

}

/* pcm->samplerate contains the sampling frequency */

nchannels = pcm->channels;

nsamples = pcm->length;

left_ch = pcm->samples[0];

right_ch = pcm->samples[1];

while (nsamples--) {

signed int sample;

/* output sample(s) in 16-bit signed little-endian PCM */

sample = scale(*left_ch++);

*out++ = ((sample >> 0) & 0xff);

*out++ = ((sample >> 8) & 0xff);

if (nchannels == 2) {

sample = scale(*right_ch++);

*out++ = ((sample >> 0) & 0xff);

*out++ = ((sample >> 8) & 0xff);

}

}

mp3_mad->output_end = out - mp3_mad->output_buffer;

/*assert(mp3_mad->output_end <= MAD_OUTPUT_BUFFER_SIZE);*/

}

mad_getSamples(mad_data *mp3_mad, Uint8 *stream, int len) {

int bytes_remaining;

int num_bytes;

Uint8 *out;

if ((mp3_mad->status & MS_playing) == 0) {

/* We're not supposed to be playing, so send silence instead. */

memset(stream, 0, len);

}

out = stream;

bytes_remaining = len;

while (bytes_remaining > 0) {

if (mp3_mad->output_end == mp3_mad->output_begin) {

/* We need to get a new frame. */

mp3_mad->output_begin = 0;

mp3_mad->output_end = 0;

if (!read_next_frame(mp3_mad)) {

if ((mp3_mad->status & MS_error_flags) != 0) {

/* Couldn't read a frame; either an error condition or

end-of-file. Stop. */

memset(out, 0, bytes_remaining);

mp3_mad->status &= ~MS_playing;

}

} else {

decode_frame(mp3_mad);

/* Now convert the frame data to the appropriate format for

output. */

mp3_mad->cvt.buf = mp3_mad->output_buffer;

mp3_mad->cvt.len = mp3_mad->output_end;

mp3_mad->output_end = (int)(mp3_mad->output_end * mp3_mad->cvt.len_ratio);

/*assert(mp3_mad->output_end <= MAD_OUTPUT_BUFFER_SIZE);*/

SDL_ConvertAudio(&mp3_mad->cvt);

}

}

num_bytes = mp3_mad->output_end - mp3_mad->output_begin;

if (bytes_remaining < num_bytes) {

num_bytes = bytes_remaining;

}

if (mp3_mad->volume == MIX_MAX_VOLUME) {

memcpy(out, mp3_mad->output_buffer + mp3_mad->output_begin, num_bytes);

} else {

SDL_MixAudio(out, mp3_mad->output_buffer + mp3_mad->output_begin,

num_bytes, mp3_mad->volume);

}

out += num_bytes;

mp3_mad->output_begin += num_bytes;

bytes_remaining -= num_bytes;

}

}

void

mad_seek(mad_data *mp3_mad, double position) {

mad_timer_t target;

int int_part;

int_part = (int)position;

mad_timer_set(&target, int_part,

(int)((position - int_part) * 1000000), 1000000);

if (mad_timer_compare(mp3_mad->next_frame_start, target) > 0) {

/* In order to seek backwards in a VBR file, we have to rewind and

start again from the beginning. This isn't necessary if the

file happens to be CBR, of course; in that case we could seek

directly to the frame we want. But I leave that little

optimization for the future developer who discovers she really

needs it. */

mp3_mad->frames_read = 0;

mad_timer_reset(&mp3_mad->next_frame_start);

mp3_mad->status &= ~MS_error_flags;

mp3_mad->output_begin = 0;

mp3_mad->output_end = 0;

}

/* Now we have to skip frames until we come to the right one.

Again, only truly necessary if the file is VBR. */

while (mad_timer_compare(mp3_mad->next_frame_start, target) < 0) {

if (!read_next_frame(mp3_mad)) {

if ((mp3_mad->status & MS_error_flags) != 0) {

/* Couldn't read a frame; either an error condition or

end-of-file. Stop. */

mp3_mad->status &= ~MS_playing;

return;

}

}

}

/* Here we are, at the beginning of the frame that contains the

target time. Ehh, I say that's close enough. If we wanted to,

we could get more precise by decoding the frame now and counting

the appropriate number of samples out of it. */

}

void

mad_setVolume(mad_data *mp3_mad, int volume) {

mp3_mad->volume = volume;

}

#endif /* MP3_MAD_MUSIC */