mpv/libmpcodecs/ad_libmad.c

// SAMPLE audio decoder - you can use this file as template when creating new codec!

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include "config.h"

#ifdef USE_LIBMAD

#include "ad_internal.h"

static ad_info_t info =  {
	"libmad mpeg audio decoder",
	"libmad",
	"A'rpi",
	"libmad...",
	"based on Xine's libmad/xine_decoder.c"
};

LIBAD_EXTERN(libmad)

#include <mad.h>

typedef struct mad_decoder_s {

  struct mad_synth  synth; 
  struct mad_stream stream;
  struct mad_frame  frame;
  
  int have_frame;

  int               output_sampling_rate;
  int               output_open;
  int               output_mode;

} mad_decoder_t;

static int preinit(sh_audio_t *sh){

  mad_decoder_t *this = (mad_decoder_t *) malloc(sizeof(mad_decoder_t));
  memset(this,0,sizeof(mad_decoder_t));
  sh->context = this;
  
  mad_synth_init  (&this->synth);
  mad_stream_init (&this->stream);
  mad_frame_init  (&this->frame);
  
  sh->audio_out_minsize=2*4608;
  sh->audio_in_minsize=4096;
  
  return 1;
}

static int read_frame(sh_audio_t *sh){
  mad_decoder_t *this = (mad_decoder_t *) sh->context;
  int len;

while((len=demux_read_data(sh->ds,&sh->a_in_buffer[sh->a_in_buffer_len],
          sh->a_in_buffer_size-sh->a_in_buffer_len))>0){
  sh->a_in_buffer_len+=len;
  while(1){
    int ret;
    mad_stream_buffer (&this->stream, sh->a_in_buffer, sh->a_in_buffer_len);
    ret=mad_frame_decode (&this->frame, &this->stream);
    if (this->stream.next_frame) {
	int num_bytes =
	    (char*)sh->a_in_buffer+sh->a_in_buffer_len - (char*)this->stream.next_frame;
	memmove(sh->a_in_buffer, this->stream.next_frame, num_bytes);
	mp_msg(MSGT_DECAUDIO,MSGL_DBG2,"libmad: %d bytes processed\n",sh->a_in_buffer_len-num_bytes);
	sh->a_in_buffer_len = num_bytes;
    }
    if (ret == 0) return 1; // OK!!!
    // error! try to resync!
    if(this->stream.error==MAD_ERROR_BUFLEN) break;
  }
}
mp_msg(MSGT_DECAUDIO,MSGL_INFO,"Cannot sync MAD frame\n");
return 0;
}

static int init(sh_audio_t *sh){
  mad_decoder_t *this = (mad_decoder_t *) sh->context;

  this->have_frame=read_frame(sh);
  if(!this->have_frame) return 0; // failed to sync...
  
  sh->channels=(this->frame.header.mode == MAD_MODE_SINGLE_CHANNEL) ? 1 : 2;
  sh->samplerate=this->frame.header.samplerate;
  sh->i_bps=this->frame.header.bitrate/8;
  sh->samplesize=2;
  
  return 1;
}

static void uninit(sh_audio_t *sh){
  mad_decoder_t *this = (mad_decoder_t *) sh->context;
  mad_synth_finish (&this->synth);
  mad_frame_finish (&this->frame);
  mad_stream_finish(&this->stream);
  free(sh->context);
}

/* utility to scale and round samples to 16 bits */
static inline 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);
}

static int decode_audio(sh_audio_t *sh,unsigned char *buf,int minlen,int maxlen){
  mad_decoder_t *this = (mad_decoder_t *) sh->context;
  int len=0;

  while(len<minlen && len+4608<=maxlen){
    if(!this->have_frame) this->have_frame=read_frame(sh);
    if(!this->have_frame) break; // failed to sync... or EOF
    this->have_frame=0;

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

	{ unsigned int         nchannels, nsamples;
	  mad_fixed_t const   *left_ch, *right_ch;
	  struct mad_pcm      *pcm = &this->synth.pcm;
	  uint16_t            *output = (uint16_t*) buf;

	  nchannels = pcm->channels;
	  nsamples  = pcm->length;
	  left_ch   = pcm->samples[0];
	  right_ch  = pcm->samples[1];

	  len+=2*nchannels*nsamples;
	  buf+=2*nchannels*nsamples;
	  
	  while (nsamples--) {
	    /* output sample(s) in 16-bit signed little-endian PCM */
	    
	    *output++ = scale(*left_ch++);
	    
	    if (nchannels == 2) 
	      *output++ = scale(*right_ch++);

	  }
	}
  }
  
  return len?len:-1;
}

static int control(sh_audio_t *sh,int cmd,void* arg, ...){
  mad_decoder_t *this = (mad_decoder_t *) sh->context;
    // various optional functions you MAY implement:
    switch(cmd){
      case ADCTRL_RESYNC_STREAM:
	this->have_frame=0;
	mad_synth_init  (&this->synth);
	mad_stream_init (&this->stream);
	mad_frame_init  (&this->frame);
	return CONTROL_TRUE;
      case ADCTRL_SKIP_FRAME:
        this->have_frame=read_frame(sh);
	return CONTROL_TRUE;
    }
  return CONTROL_UNKNOWN;
}
#endif