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/*
* Simple mp3 player. Derived from libmad's example minimad.c.
*/
#include <u.h>
#include <libc.h>
#include "mad.h"
/* Current input file */
char *name;
vlong offset;
int rate = 44100;
char *outfile;
int vfd; /* /dev/volume */
static enum mad_flow
input(void *data, struct mad_stream *stream)
{
int fd, n, m;
static uchar buf[32768];
fd = (int)data;
n = stream->bufend - stream->next_frame;
memmove(buf, stream->next_frame, n);
m = read(fd, buf+n, sizeof buf-n);
offset += m;
if(m < 0)
sysfatal("reading input: %r");
if(m == 0)
return MAD_FLOW_STOP;
n += m;
mad_stream_buffer(stream, buf, n);
return MAD_FLOW_CONTINUE;
}
/*
* Dither 28-bit down to 16-bit. From mpg321.
* I'm skeptical, but it's supposed to make the
* samples sound better than just truncation.
*/
typedef struct Dither Dither;
struct Dither
{
mad_fixed_t error[3];
mad_fixed_t random;
};
#define PRNG(x) (((x)*0x19660dL + 0x3c6ef35fL) & 0xffffffffL)
enum
{
FracBits = MAD_F_FRACBITS,
OutBits = 16,
Round = 1 << (FracBits+1-OutBits-1), // sic
ScaleBits = FracBits + 1 - OutBits,
LowMask = (1<<ScaleBits) - 1,
Min = -MAD_F_ONE,
Max = MAD_F_ONE - 1,
};
int
audiodither(mad_fixed_t v, Dither *d)
{
int out;
mad_fixed_t random;
/* noise shape */
v += d->error[0] - d->error[1] + d->error[2];
d->error[2] = d->error[1];
d->error[1] = d->error[0] / 2;
/* bias */
out = v + Round;
/* dither */
random = PRNG(d->random);
out += (random & LowMask) - (d->random & LowMask);
d->random = random;
/* clip */
if(out > Max){
out = Max;
if(v > Max)
v = Max;
}else if(out < Min){
out = Min;
if(v < Min)
v = Min;
}
/* quantize */
out &= ~LowMask;
/* error feedback */
d->error[0] = v - out;
/* scale */
return out >> ScaleBits;
}
static enum mad_flow
output(void *data, struct mad_header const* header, struct mad_pcm *pcm)
{
int i, n, v;
mad_fixed_t const *left, *right;
static Dither d;
static uchar buf[16384], *p;
if(pcm->samplerate != rate){
rate = pcm->samplerate;
if(vfd < 0)
fprint(2, "warning: audio sample rate is %d Hz\n", rate);
else
fprint(vfd, "speed %d", rate);
}
p = buf;
memset(&d, 0, sizeof d);
n = pcm->length;
switch(pcm->channels){
case 1:
left = pcm->samples[0];
for(i=0; i<n; i++){
v = audiodither(*left++, &d);
/* stereoize */
*p++ = v;
*p++ = v>>8;
*p++ = v;
*p++ = v>>8;
}
break;
case 2:
left = pcm->samples[0];
right = pcm->samples[1];
for(i=0; i<n; i++){
v = audiodither(*left++, &d);
*p++ = v;
*p++ = v>>8;
v = audiodither(*right++, &d);
*p++ = v;
*p++ = v>>8;
}
break;
}
assert(p<=buf+sizeof buf);
write(1, buf, p-buf);
return MAD_FLOW_CONTINUE;
}
static enum mad_flow
error(void *data, struct mad_stream *stream, struct mad_frame *frame)
{
if(stream->error == MAD_ERROR_LOSTSYNC)
return MAD_FLOW_CONTINUE;
sysfatal("%s:#%lld: %s",
name, offset-(stream->bufend-stream->next_frame),
mad_stream_errorstr(stream));
return 0;
}
void
play(int fd, char *nam)
{
struct mad_decoder decoder;
name = nam;
mad_decoder_init(&decoder, (void*)fd, input, nil, nil, output, error, nil);
mad_decoder_run(&decoder, MAD_DECODER_MODE_SYNC);
mad_decoder_finish(&decoder);
}
void
usage(void)
{
fprint(2, "usage: mp3dec [-o outfile] [file...]\n");
exits("usage");
}
void
main(int argc, char **argv)
{
int i, fd;
char *p;
ARGBEGIN{
case 'o':
outfile = EARGF(usage());
break;
default:
usage();
}ARGEND
if(outfile){
if((fd = create(outfile, OWRITE, 0666)) < 0)
sysfatal("create %s: %r", outfile);
}else{
if((fd = open("/dev/audio", OWRITE)) < 0)
sysfatal("open /dev/audio: %r");
vfd = open("/dev/volume", OWRITE);
}
if(fd != 1){
dup(fd, 1);
close(fd);
}
if(argc == 0){
play(0, "standard input");
}else{
for(i=0; i<argc; i++){
if((fd = open(argv[i], OREAD)) < 0)
sysfatal("open %s: %r", argv[i]);
play(fd, argv[i]);
close(fd);
}
}
exits(0);
}
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