toolame-02l/availbits.c

   1 /*
   2  * toolame - an optimized mpeg 1/2 layer 2 audio encoder
   3  * Copyright (C) 2001 Michael Cheng
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  *  You should have received a copy of the GNU General Public License
  16  *  along with this program; if not, write to the Free Software
  17  *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  18  */
  19 #include <stdio.h>
  20 #include "common.h"
  21 #include "encoder.h"
  22 #include "musicin.h"
  23 #include "options.h"
  24 #include "availbits.h"
  25
  26
  27 struct slotinfo {
  28   double average;
  29   double frac;
  30   int whole;
  31   double lag;
  32   int extra;
  33 } slots;
  34
  35 /* function returns the number of available bits */
  36 int available_bits (frame_header *header, options * glopts)
  37 {
  38   int adb;
  39
  40   slots.extra = 0;              /* be default, no extra slots */
  41
  42   slots.average =
  43     (1152.0 / s_freq[header->version][header->sampling_frequency]) *
  44     ((double) bitrate[header->version][header->bitrate_index] / 8.0);
  45
  46   slots.whole = (int) slots.average;
  47   slots.frac = slots.average - (double) slots.whole;
  48
  49   /* never allow padding for a VBR frame.
  50      Don't ask me why, I've forgotten why I set this */
  51   if (slots.frac != 0 && glopts->usepadbit && glopts->vbr == FALSE) {
  52     if (slots.lag > (slots.frac - 1.0)) {       /* no padding for this frame */
  53       slots.lag -= slots.frac;
  54       slots.extra = 0;
  55       header->padding = 0;
  56     } else {                    /* padding */
  57
  58       slots.extra = 1;
  59       header->padding = 1;
  60       slots.lag += (1 - slots.frac);
  61     }
  62   }
  63
  64   adb = (slots.whole + slots.extra) * 8;
  65
  66   return adb;
  67 }