1/* ------------------------------------------------------------------
2 * Copyright (C) 1998-2009 PacketVideo
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
13 * express or implied.
14 * See the License for the specific language governing permissions
15 * and limitations under the License.
16 * -------------------------------------------------------------------
17 */
18/*
19------------------------------------------------------------------------------
20
21   PacketVideo Corp.
22   MP3 Decoder Library
23
24   Filename: pvmp3_decode_header.cpp
25
26     Date: 09/21/2007
27
28------------------------------------------------------------------------------
29 REVISION HISTORY
30
31
32 Description:
33
34------------------------------------------------------------------------------
35 INPUT AND OUTPUT DEFINITIONS
36
37Input
38    tbits  *inputStream,        bit stream
39    mp3Header  *info,
40    uint32 *crc
41 Returns
42
43    mp3Header  *info,           structure holding the parsed mp3 header info
44    uint32 *crc                 initialized crc computation
45
46
47------------------------------------------------------------------------------
48 FUNCTION DESCRIPTION
49
50    gets mp3 header information
51
52------------------------------------------------------------------------------
53 REQUIREMENTS
54
55
56------------------------------------------------------------------------------
57 REFERENCES
58
59 [1] ISO MPEG Audio Subgroup Software Simulation Group (1996)
60     ISO 13818-3 MPEG-2 Audio Decoder - Lower Sampling Frequency Extension
61
62------------------------------------------------------------------------------
63 PSEUDO-CODE
64
65------------------------------------------------------------------------------
66*/
67
68
69/*----------------------------------------------------------------------------
70; INCLUDES
71----------------------------------------------------------------------------*/
72
73#include "pvmp3_decode_header.h"
74#include "pvmp3_crc.h"
75#include "pvmp3_getbits.h"
76#include "pvmp3_seek_synch.h"
77
78
79/*----------------------------------------------------------------------------
80; MACROS
81; Define module specific macros here
82----------------------------------------------------------------------------*/
83
84
85/*----------------------------------------------------------------------------
86; DEFINES
87; Include all pre-processor statements here. Include conditional
88; compile variables also.
89----------------------------------------------------------------------------*/
90
91/*----------------------------------------------------------------------------
92; LOCAL FUNCTION DEFINITIONS
93; Function Prototype declaration
94----------------------------------------------------------------------------*/
95
96/*----------------------------------------------------------------------------
97; LOCAL STORE/BUFFER/POINTER DEFINITIONS
98; Variable declaration - defined here and used outside this module
99----------------------------------------------------------------------------*/
100
101/*----------------------------------------------------------------------------
102; EXTERNAL FUNCTION REFERENCES
103; Declare functions defined elsewhere and referenced in this module
104----------------------------------------------------------------------------*/
105
106/*----------------------------------------------------------------------------
107; EXTERNAL GLOBAL STORE/BUFFER/POINTER REFERENCES
108; Declare variables used in this module but defined elsewhere
109----------------------------------------------------------------------------*/
110
111/*----------------------------------------------------------------------------
112; FUNCTION CODE
113----------------------------------------------------------------------------*/
114
115ERROR_CODE pvmp3_decode_header(tmp3Bits  *inputStream,
116                               mp3Header  *info,
117                               uint32 *crc)
118{
119
120    ERROR_CODE err = NO_DECODING_ERROR;
121    uint32  temp;
122
123    /*
124     * Verify that at least the header is complete
125     * Note that SYNC_WORD_LNGTH is in unit of bits, but inputBufferCurrentLength
126     * is in unit of bytes.
127     */
128    if (inputStream->inputBufferCurrentLength < ((SYNC_WORD_LNGTH + 21) >> 3))
129    {
130        return NO_ENOUGH_MAIN_DATA_ERROR;
131    }
132
133    /*
134     *  MPEG Audio Version ID
135     */
136    temp = getUpTo17bits(inputStream, SYNC_WORD_LNGTH);
137    if ((temp & SYNC_WORD) != SYNC_WORD)
138    {
139        err = pvmp3_header_sync(inputStream);
140
141        if (err != NO_DECODING_ERROR)
142        {
143            return err;
144        }
145    }
146
147    temp = getNbits(inputStream, 21);   // to avoid multiple bitstream accesses
148
149
150    switch (temp >> 19)  /* 2 */
151    {
152        case 0:
153            info->version_x = MPEG_2_5;
154            break;
155        case 2:
156            info->version_x = MPEG_2;
157            break;
158        case 3:
159            info->version_x = MPEG_1;
160            break;
161        default:
162            info->version_x = INVALID_VERSION;
163            err = UNSUPPORTED_LAYER;
164            break;
165    }
166
167    info->layer_description  = 4 - ((temp << 13) >> 30);  /* 2 */
168    info->error_protection   =  !((temp << 15) >> 31);  /* 1 */
169
170    if (info->error_protection)
171    {
172        *crc = 0xffff;           /* CRC start value */
173        calculate_crc((temp << 16) >> 16, 16, crc);
174    }
175
176    info->bitrate_index      = (temp << 16) >> 28;  /* 4 */
177    info->sampling_frequency = (temp << 20) >> 30;  /* 2 */
178    info->padding            = (temp << 22) >> 31;  /* 1 */
179    info->extension          = (temp << 23) >> 31;  /* 1 */
180    info->mode               = (temp << 24) >> 30;  /* 2 */
181    info->mode_ext           = (temp << 26) >> 30;  /* 2 */
182    info->copyright          = (temp << 27) >> 31;  /* 1 */
183    info->original           = (temp << 28) >> 31;  /* 1 */
184    info->emphasis           = (temp << 30) >> 30;  /* 2 */
185
186
187    if (!info->bitrate_index || info->sampling_frequency == 3)
188    {
189        err = UNSUPPORTED_FREE_BITRATE;
190    }
191
192    return(err);
193}
194
195