/* * libmad - MPEG audio decoder library * Copyright (C) 2000-2004 Underbit Technologies, Inc. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program 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 General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA * * $Id: frame.c,v 1.29 2004/02/04 22:59:19 rob Exp $ */# ifdef HAVE_CONFIG_H#  include "config.h"# endif# include "global.h"# include <stdlib.h># include "bit.h"# include "stream.h"# include "frame.h"# include "timer.h"# include "layer12.h"# include "layer3.h"staticunsigned long const bitrate_table[5][15] = {  /* MPEG-1 */  { 0,  32000,  64000,  96000, 128000, 160000, 192000, 224000,  /* Layer I   */       256000, 288000, 320000, 352000, 384000, 416000, 448000 },  { 0,  32000,  48000,  56000,  64000,  80000,  96000, 112000,  /* Layer II  */       128000, 160000, 192000, 224000, 256000, 320000, 384000 },  { 0,  32000,  40000,  48000,  56000,  64000,  80000,  96000,  /* Layer III */       112000, 128000, 160000, 192000, 224000, 256000, 320000 },  /* MPEG-2 LSF */  { 0,  32000,  48000,  56000,  64000,  80000,  96000, 112000,  /* Layer I   */       128000, 144000, 160000, 176000, 192000, 224000, 256000 },  { 0,   8000,  16000,  24000,  32000,  40000,  48000,  56000,  /* Layers    */        64000,  80000,  96000, 112000, 128000, 144000, 160000 } /* II & III  */};staticunsigned int const samplerate_table[3] = { 44100, 48000, 32000 };staticint (*const decoder_table[3])(struct mad_stream *, struct mad_frame *) = { mad_layer_I,  mad_layer_II,  mad_layer_III};/* * NAME:	header->init() * DESCRIPTION:	initialize header struct */void mad_header_init(struct mad_header *header){  header->layer          = 0;  header->mode           = 0;  header->mode_extension = 0;  header->emphasis       = 0;  header->bitrate        = 0;  header->samplerate     = 0;  header->crc_check      = 0;  header->crc_target     = 0;  header->flags          = 0;  header->private_bits   = 0;  header->duration       = mad_timer_zero;}/* * NAME:	frame->init() * DESCRIPTION:	initialize frame struct */void mad_frame_init(struct mad_frame *frame){  mad_header_init(&frame->header);  frame->options = 0;  frame->overlap = 0;  mad_frame_mute(frame);}/* * NAME:	frame->finish() * DESCRIPTION:	deallocate any dynamic memory associated with frame */void mad_frame_finish(struct mad_frame *frame){  mad_header_finish(&frame->header);  if (frame->overlap) {    free(frame->overlap);    frame->overlap = 0;  }}/* * NAME:	decode_header() * DESCRIPTION:	read header data and following CRC word */staticint decode_header(struct mad_header *header, struct mad_stream *stream){  unsigned int index;  header->flags        = 0;  header->private_bits = 0;  /* header() */  /* syncword */  mad_bit_skip(&stream->ptr, 11);  /* MPEG 2.5 indicator (really part of syncword) */  if (mad_bit_read(&stream->ptr, 1) == 0)    header->flags |= MAD_FLAG_MPEG_2_5_EXT;  /* ID */  if (mad_bit_read(&stream->ptr, 1) == 0)    header->flags |= MAD_FLAG_LSF_EXT;  else if (header->flags & MAD_FLAG_MPEG_2_5_EXT) {    stream->error = MAD_ERROR_LOSTSYNC;    return -1;  }  /* layer */  header->layer = 4 - mad_bit_read(&stream->ptr, 2);  if (header->layer == 4) {    stream->error = MAD_ERROR_BADLAYER;    return -1;  }  /* protection_bit */  if (mad_bit_read(&stream->ptr, 1) == 0) {    header->flags    |= MAD_FLAG_PROTECTION;    header->crc_check = mad_bit_crc(stream->ptr, 16, 0xffff);  }  /* bitrate_index */  index = mad_bit_read(&stream->ptr, 4);  if (index == 15) {    stream->error = MAD_ERROR_BADBITRATE;    return -1;  }  if (header->flags & MAD_FLAG_LSF_EXT)    header->bitrate = bitrate_table[3 + (header->layer >> 1)][index];  else    header->bitrate = bitrate_table[header->layer - 1][index];  /* sampling_frequency */  index = mad_bit_read(&stream->ptr, 2);  if (index == 3) {    stream->error = MAD_ERROR_BADSAMPLERATE;    return -1;  }  header->samplerate = samplerate_table[index];  if (header->flags & MAD_FLAG_LSF_EXT) {    header->samplerate /= 2;    if (header->flags & MAD_FLAG_MPEG_2_5_EXT)      header->samplerate /= 2;  }  /* padding_bit */  if (mad_bit_read(&stream->ptr, 1))    header->flags |= MAD_FLAG_PADDING;  /* private_bit */  if (mad_bit_read(&stream->ptr, 1))    header->private_bits |= MAD_PRIVATE_HEADER;  /* mode */  header->mode = 3 - mad_bit_read(&stream->ptr, 2);  /* mode_extension */  header->mode_extension = mad_bit_read(&stream->ptr, 2);  /* copyright */  if (mad_bit_read(&stream->ptr, 1))    header->flags |= MAD_FLAG_COPYRIGHT;  /* original/copy */  if (mad_bit_read(&stream->ptr, 1))    header->flags |= MAD_FLAG_ORIGINAL;  /* emphasis */  header->emphasis = mad_bit_read(&stream->ptr, 2);# if defined(OPT_STRICT)  /*   * ISO/IEC 11172-3 says this is a reserved emphasis value, but   * streams exist which use it anyway. Since the value is not important   * to the decoder proper, we allow it unless OPT_STRICT is defined.   */  if (header->emphasis == MAD_EMPHASIS_RESERVED) {    stream->error = MAD_ERROR_BADEMPHASIS;    return -1;  }# endif  /* error_check() */  /* crc_check */  if (header->flags & MAD_FLAG_PROTECTION)    header->crc_target = mad_bit_read(&stream->ptr, 16);  return 0;}/* * NAME:	free_bitrate() * DESCRIPTION:	attempt to discover the bitstream's free bitrate */staticint free_bitrate(struct mad_stream *stream, struct mad_header const *header){  struct mad_bitptr keep_ptr;  unsigned long rate = 0;  unsigned int pad_slot, slots_per_frame;  unsigned char const *ptr = 0;  keep_ptr = stream->ptr;  pad_slot = (header->flags & MAD_FLAG_PADDING) ? 1 : 0;  slots_per_frame = (header->layer == MAD_LAYER_III &&		     (header->flags & MAD_FLAG_LSF_EXT)) ? 72 : 144;  while (mad_stream_sync(stream) == 0) {    struct mad_stream peek_stream;    struct mad_header peek_header;    peek_stream = *stream;    peek_header = *header;    if (decode_header(&peek_header, &peek_stream) == 0 &&	peek_header.layer == header->layer &&	peek_header.samplerate == header->samplerate) {      unsigned int N;      ptr = mad_bit_nextbyte(&stream->ptr);      N = ptr - stream->this_frame;      if (header->layer == MAD_LAYER_I) {	rate = (unsigned long) header->samplerate *	  (N - 4 * pad_slot + 4) / 48 / 1000;      }      else {	rate = (unsigned long) header->samplerate *	  (N - pad_slot + 1) / slots_per_frame / 1000;      }      if (rate >= 8)	break;    }    mad_bit_skip(&stream->ptr, 8);  }  stream->ptr = keep_ptr;  if (rate < 8 || (header->layer == MAD_LAYER_III && rate > 640)) {    stream->error = MAD_ERROR_LOSTSYNC;    return -1;  }  stream->freerate = rate * 1000;  return 0;}/* * NAME:	header->decode() * DESCRIPTION:	read the next frame header from the stream */int mad_header_decode(struct mad_header *header, struct mad_stream *stream){  register unsigned char const *ptr, *end;  unsigned int pad_slot, N;  ptr = stream->next_frame;  end = stream->bufend;  if (ptr == 0) {    stream->error = MAD_ERROR_BUFPTR;    goto fail;  }  /* stream skip */  if (stream->skiplen) {    if (!stream->sync)      ptr = stream->this_frame;    if (end - ptr < stream->skiplen) {      stream->skiplen   -= end - ptr;      stream->next_frame = end;      stream->error = MAD_ERROR_BUFLEN;      goto fail;    }    ptr += stream->skiplen;    stream->skiplen = 0;    stream->sync = 1;  } sync:  /* synchronize */  if (stream->sync) {    if (end - ptr < MAD_BUFFER_GUARD) {      stream->next_frame = ptr;      stream->error = MAD_ERROR_BUFLEN;      goto fail;    }    else if (!(ptr[0] == 0xff && (ptr[1] & 0xe0) == 0xe0)) {      /* mark point where frame sync word was expected */      stream->this_frame = ptr;      stream->next_frame = ptr + 1;      stream->error = MAD_ERROR_LOSTSYNC;      goto fail;    }  }  else {    mad_bit_init(&stream->ptr, ptr);					//第一次初始化    if (mad_stream_sync(stream) == -1) {      if (end - stream->next_frame >= MAD_BUFFER_GUARD)	stream->next_frame = end - MAD_BUFFER_GUARD;      stream->error = MAD_ERROR_BUFLEN;      goto fail;    }    ptr = mad_bit_nextbyte(&stream->ptr);  }  /* begin processing */  stream->this_frame = ptr;  stream->next_frame = ptr + 1;  /* possibly bogus sync word */  mad_bit_init(&stream->ptr, stream->this_frame);  if (decode_header(header, stream) == -1)		//第一次解頭，調用了mad_bit_skip    goto fail;  /* calculate frame duration */  mad_timer_set(&header->duration, 0,		32 * MAD_NSBSAMPLES(header), header->samplerate);  /* calculate free bit rate */  if (header->bitrate == 0) {    if ((stream->freerate == 0 || !stream->sync ||	 (header->layer == MAD_LAYER_III && stream->freerate > 640000)) &&	free_bitrate(stream, header) == -1)      goto fail;    header->bitrate = stream->freerate;    header->flags  |= MAD_FLAG_FREEFORMAT;  }  /* calculate beginning of next frame */  pad_slot = (header->flags & MAD_FLAG_PADDING) ? 1 : 0;  if (header->layer == MAD_LAYER_I)    N = ((12 * header->bitrate / header->samplerate) + pad_slot) * 4;  else {    unsigned int slots_per_frame;    slots_per_frame = (header->layer == MAD_LAYER_III &&		       (header->flags & MAD_FLAG_LSF_EXT)) ? 72 : 144;    N = (slots_per_frame * header->bitrate / header->samplerate) + pad_slot;  }  /* verify there is enough data left in buffer to decode this frame */  if (N + MAD_BUFFER_GUARD > end - stream->this_frame) {    stream->next_frame = stream->this_frame;    stream->error = MAD_ERROR_BUFLEN;    goto fail;  }  stream->next_frame = stream->this_frame + N;  if (!stream->sync) {    /* check that a valid frame header follows this frame */    ptr = stream->next_frame;    if (!(ptr[0] == 0xff && (ptr[1] & 0xe0) == 0xe0)) {      ptr = stream->next_frame = stream->this_frame + 1;      goto sync;    }    stream->sync = 1;  }  header->flags |= MAD_FLAG_INCOMPLETE;  return 0; fail:  stream->sync = 0;  return -1;}/* NAME:	frame->decode() DESCRIPTION:	decode a single frame from a bitstream */int mad_frame_decode(struct mad_frame *frame, struct mad_stream *stream){  frame->options = stream->options;  /* header() */  /* error_check() */  if (!(frame->header.flags & MAD_FLAG_INCOMPLETE) && mad_header_decode(&frame->header, stream) == -1)    goto fail;  /* audio_data() */  frame->header.flags &= ~MAD_FLAG_INCOMPLETE;  if (decoder_table[frame->header.layer - 1](stream, frame) == -1)   {  if (!MAD_RECOVERABLE(stream->error))  stream->next_frame = stream->this_frame;     goto fail;  }  /* ancillary_data() */  if (frame->header.layer != MAD_LAYER_III)   { struct mad_bitptr next_frame;    mad_bit_init(&next_frame, stream->next_frame);    stream->anc_ptr    = stream->ptr;    stream->anc_bitlen = mad_bit_length(&stream->ptr, &next_frame);    mad_bit_finish(&next_frame);  }  return 0; fail:  stream->anc_bitlen = 0;  return -1;}/* * NAME:	frame->mute() * DESCRIPTION:	zero all subband values so the frame becomes silent */void mad_frame_mute(struct mad_frame *frame){  unsigned int s, sb;  for (s = 0; s < 36; ++s) {    for (sb = 0; sb < 32; ++sb) {      frame->sbsample[0][s][sb] =      frame->sbsample[1][s][sb] = 0;    }  }  if (frame->overlap) {    for (s = 0; s < 18; ++s) {      for (sb = 0; sb < 32; ++sb) {	(*frame->overlap)[0][sb][s] =	(*frame->overlap)[1][sb][s] = 0;      }    }  }}