adts.c

/*
 * Support for ISO/IEC 14496-3:2001(E) AAC ADTS audio streams.
 *
 * ***** BEGIN LICENSE BLOCK *****
 * Version: MPL 1.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 * http://www.mozilla.org/MPL/
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is the MPEG TS, PS and ES tools.
 *
 * The Initial Developer of the Original Code is Amino Communications Ltd.
 * Portions created by the Initial Developer are Copyright (C) 2008
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Amino Communications Ltd, Swavesey, Cambridge UK
 *
 * ***** END LICENSE BLOCK *****
 */

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

#include "compat.h"
#include "printing_fns.h"
#include "misc_fns.h"
#include "adts_fns.h"

#define DEBUG 0

/*
 * Read the next ADTS frame.
 *
 * Assumes that the input stream is synchronised - i.e., it does not
 * try to cope if the next three bytes are not '1111 1111 1111'.
 *
 * - `file` is the file descriptor of the ADTS file to read from
 * - `frame` is the ADTS frame that is read
 * - `flags` indicates if we are forcing the recognition of "emphasis"
 *   fields, etc.
 *
 * Returns 0 if all goes well, EOF if end-of-file is read, and 1 if something
 * goes wrong.
 */
extern int read_next_adts_frame(int            file,
                                audio_frame_p *frame,
                                unsigned int   flags)
{
#define JUST_ENOUGH 6 // just enough to hold the bits of the headers we want

  int    err, ii;
  int    id, layer;
  byte   header[JUST_ENOUGH];
  byte  *data = NULL;
  int    frame_length;
  int    has_emphasis = 0;

  offset_t  posn = tell_file(file);
#if DEBUG
  fprint_msg("Offset: " OFFSET_T_FORMAT "\n",posn);
#endif

  err = read_bytes(file,JUST_ENOUGH,header);
  if (err == EOF)
    return EOF;
  else if (err)
  {
    fprint_err("### Error reading header bytes of ADTS frame\n"
               "    (in frame starting at " OFFSET_T_FORMAT ")\n",posn);
    free(data);
    return 1;
  }

#if DEBUG
  print_msg("ADTS frame\n");
  print_data(TRUE,"Start",header,JUST_ENOUGH,JUST_ENOUGH);
#endif

  if (header[0] != 0xFF || (header[1] & 0xF0) != 0xF0)
  {
    fprint_err("### ADTS frame does not start with '1111 1111 1111'"
               " syncword - lost synchronisation?\n"
               "    Found 0x%X%X%X instead of 0xFFF\n",
               (unsigned)(header[0] & 0xF0) >> 4,
               (header[0] & 0x0F),
               (unsigned)(header[1] & 0xF0) >> 4);
    fprint_err("    (in frame starting at " OFFSET_T_FORMAT ")\n",posn);
    return 1;
  }

  id = (header[1] & 0x08) >> 3;
#if DEBUG
  fprint_msg("   ID %d (%s)\n",id,(id==1?"MPEG-2 AAC":"MPEG-4"));
#endif
  layer = (header[1] & 0x06) >> 1;
  if (layer != 0)
    fprint_msg("   layer is %d, not 0 (in frame at " OFFSET_T_FORMAT ")\n",
               layer,posn);

  // Experience appears to show that emphasis doesn't exist in MPEG-2 AVC.
  // But it does exist in (ID=1) MPEG-4 streams.
  // 
  // .. or if forced.

  has_emphasis = (flags & ADTS_FLAG_NO_EMPHASIS) ? 0 :
    ((flags & ADTS_FLAG_FORCE_EMPHASIS) || !id);

  if (!has_emphasis)
  {
    frame_length = ((header[3] & 0x03) << 11) | (header[4] << 3) |
      ((unsigned)(header[5] & 0xE0) >> 5);
  }
  else
  {
    frame_length = (header[4] << 5) | ((unsigned)(header[5] & 0xF8) >> 3);
  }
#if DEBUG
  fprint_msg("   length %d\n",frame_length);
#endif

  data = malloc(frame_length);
  if (data == NULL)
  {
    print_err("### Unable to extend data buffer for ADTS frame\n");
    free(data);
    return 1;
  }

  for (ii=0; ii<JUST_ENOUGH; ii++)
    data[ii] = header[ii];

  err = read_bytes(file,frame_length - JUST_ENOUGH,&(data[JUST_ENOUGH]));
  if (err)
  {
    if (err == EOF)
      print_err("### Unexpected EOF reading rest of ADTS frame\n");
    else
      print_err("### Error reading rest of ADTS frame\n");
    free(data);
    return 1;
  }
#if DEBUG
  print_data(TRUE,"Again",data,frame_length,20);
#endif

  err = build_audio_frame(frame);
  if (err)
  {
    free(data);
    return 1;
  }
  (*frame)->data = data;
  (*frame)->data_len = frame_length;

  return 0;
}

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