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1 // Copyright (c) 2006-2009 Nokia Corporation and/or its subsidiary(-ies). |
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2 // All rights reserved. |
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3 // This component and the accompanying materials are made available |
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4 // under the terms of "Eclipse Public License v1.0" |
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5 // which accompanies this distribution, and is available |
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6 // at the URL "http://www.eclipse.org/legal/epl-v10.html". |
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7 // |
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8 // Initial Contributors: |
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9 // Nokia Corporation - initial contribution. |
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10 // |
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11 // Contributors: |
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12 // |
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13 // Description: |
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14 // |
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15 |
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16 #include "constants.h" |
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17 #include "parsers.h" |
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18 |
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19 // The length of the frame in written directly into the header. |
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20 // It is 13 bits in length and spans 3 bytes. |
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21 |
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22 #define AAC_SYNC1_MASK 0xff // 11111111 |
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23 #define AAC_SYNC2_MASK 0xf0 // 11110000 |
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24 #define AAC_FRAME_LENGTH_MASK1 0x03 // 00000011 |
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25 #define AAC_FRAME_LENGTH_MASK2 0xff // 11111111 |
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26 #define AAC_FRAME_LENGTH_MASK3 0xe0 // 11100000 |
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27 #define AAC_LAYER_MASK 0x06 // 00000110 |
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28 |
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29 #define AAC_GET_SYNC1(d) (d) |
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30 #define AAC_GET_SYNC2(d) ((d & AAC_SYNC2_MASK) >> 4) |
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31 #define AAC_GET_LAYER(d) (((d) & AAC_LAYER_MASK) >> 1) |
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32 #define AAC_GET_FRAME_LENGTH(a, b, c) \ |
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33 (((a) & AAC_FRAME_LENGTH_MASK1) << 11) | \ |
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34 (((b) & AAC_FRAME_LENGTH_MASK2) << 03) | \ |
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35 (((c) & AAC_FRAME_LENGTH_MASK3) >> 05) |
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36 |
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37 |
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38 #define AAC_IS_BAD_SYNC1(s) ((s) != 0xff) |
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39 #define AAC_IS_BAD_SYNC2(s) ((s) != 0x0f) |
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40 #define AAC_IS_BAD_LAYER(l) ((l) != 0x00) |
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41 #define AAC_IS_BAD_FRAME_LENGTH(l) ((l) < KAACFrameHeaderSize) |
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42 |
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43 // |
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44 // The various states the recognition process goes through. |
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45 // |
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46 typedef enum |
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47 { |
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48 ESearchFrame1, |
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49 ESearchFrame2 |
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50 } |
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51 TAACState; |
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52 |
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53 // |
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54 // This truth table maps the following flags to a confidence level. |
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55 // |
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56 // A: Extension identified. |
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57 // B: Frame1 found. |
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58 // C: Frame2 found. |
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59 // |
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60 // C B A -> Confidence |
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61 // =================== |
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62 // 0 0 0 -> ENotRecognised |
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63 // 0 0 1 -> EPossible |
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64 // 0 1 0 -> EProbable |
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65 // 0 1 1 -> ECertain |
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66 // 1 0 0 -> ENotRecognised (Can't have f2 without f1) |
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67 // 1 0 1 -> ENotRecognised (Can't have f2 without f1) |
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68 // 1 1 0 -> EProbable |
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69 // 1 1 1 -> ECertain |
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70 // |
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71 static const TInt KAACFlagsToConfidence[8] = |
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72 { |
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73 KConfNotRecognised, |
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74 KConfPossible, |
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75 KConfProbable, |
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76 KConfCertain, |
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77 KConfNotRecognised, |
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78 KConfNotRecognised, |
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79 KConfProbable, |
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80 KConfCertain |
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81 }; |
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82 |
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83 #define KAACConfidenceMask 0x07 // [0000 0111] |
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84 #define KAACFrame1Bit KBit1 |
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85 #define KAACFrame2Bit KBit2 |
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86 |
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87 |
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88 |
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89 // |
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90 // Constructs a TAACParser on the stack. |
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91 // |
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92 TAACParser::TAACParser(CReader& aReader, TFlags& aFlags) |
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93 : iReader(aReader), |
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94 iFlags(aFlags) |
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95 { |
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96 } |
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97 |
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98 |
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99 // |
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100 // |
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101 // |
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102 void TAACParser::DoRecognise(const TDesC& aFileExt, CReader& aReader, TMatch& aMatch) |
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103 { |
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104 TFlags flags; |
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105 TBool extMatch; |
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106 |
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107 // See if the extension is recognised. |
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108 extMatch = (aFileExt.MatchF(TPtrC(KExtAAC)) != KErrNotFound); |
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109 |
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110 // Try to match a known header. |
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111 if (aReader.Match(TPtrC8(_S8("ADIF*")))) |
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112 { |
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113 aMatch.iConfidence = (extMatch ? KConfCertain : KConfProbable); |
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114 aMatch.iMime = KMimeAAC; |
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115 return; |
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116 } |
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117 |
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118 // No known header so try to parse it. |
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119 // Parsing uses flags to track what has been identified. |
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120 if (extMatch) |
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121 { |
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122 flags.SetExtensionFlag(); |
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123 } |
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124 |
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125 TAACParser parser(aReader, flags); |
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126 TRAP_IGNORE(parser.ParseL()); |
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127 |
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128 TInt confIndex = flags.GetBitField(KAACConfidenceMask); |
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129 aMatch.iConfidence = KAACFlagsToConfidence[confIndex]; |
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130 if (aMatch.iConfidence != KConfNotRecognised) |
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131 { |
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132 aMatch.iMime = KMimeAAC; |
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133 } |
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134 } |
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135 |
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136 |
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137 // |
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138 // Looks for valid AAC frame headers; at the current position |
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139 // and immediately after (if one found). |
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140 // |
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141 void TAACParser::ParseL() |
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142 { |
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143 TInt frameLength; |
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144 TAACState state = ESearchFrame1; |
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145 |
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146 // Check if it's an ADTS (raw) format AAC file. |
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147 // There's no known metadata tag for AAC so the |
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148 // first frame header should be at the start of the buffer. |
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149 |
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150 FOREVER |
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151 { |
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152 TID3Parser::ReadAndSkipID3L(iReader); |
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153 |
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154 TInt err = CheckForFrameHeaderL(frameLength); |
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155 if (err == KErrNotFound) |
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156 { |
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157 return; |
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158 } |
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159 |
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160 switch (state) |
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161 { |
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162 case ESearchFrame1: |
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163 iFlags.SetBit(KAACFrame1Bit); |
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164 state = ESearchFrame2; |
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165 break; |
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166 |
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167 case ESearchFrame2: |
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168 iFlags.SetBit(KAACFrame2Bit); |
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169 return; |
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170 } |
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171 |
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172 // Skip over the audio frame. |
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173 // This should be done after flags have been set. |
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174 iReader.SeekL(frameLength - KAACFrameHeaderSize); |
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175 }; |
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176 } |
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177 |
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178 |
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179 // |
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180 // Looks for valid AAC frame header bit patterns. |
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181 // If one is not found KErrNotFound is returned and aFrameLength |
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182 // remains unchanged. If one is found KErrNone is retured and |
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183 // aFrameLength is set to the length of the frame. |
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184 // |
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185 TInt TAACParser::CheckForFrameHeaderL(TInt& aFrameLength) |
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186 { |
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187 TBuf8<KAACFrameHeaderSize> header; |
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188 |
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189 header.SetLength(KAACFrameHeaderSize); |
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190 iReader.ReadBytesL(header); |
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191 |
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192 do |
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193 { |
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194 if (AAC_IS_BAD_SYNC1(AAC_GET_SYNC1(header[0]))) |
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195 { |
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196 break; |
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197 } |
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198 |
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199 if (AAC_IS_BAD_SYNC2(AAC_GET_SYNC2(header[1]))) |
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200 { |
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201 break; |
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202 } |
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203 |
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204 if (AAC_IS_BAD_LAYER(AAC_GET_LAYER(header[1]))) |
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205 { |
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206 break; |
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207 } |
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208 |
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209 TInt frameLength = AAC_GET_FRAME_LENGTH(header[3], header[4], header[5]); |
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210 if (AAC_IS_BAD_FRAME_LENGTH(frameLength)) |
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211 { |
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212 break; |
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213 } |
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214 // All is ok. |
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215 aFrameLength = frameLength; |
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216 return KErrNone; |
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217 } |
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218 while (EFalse); |
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219 |
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220 // No frame header was found. |
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221 aFrameLength = 0; |
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222 iReader.SeekL(-KAACFrameHeaderSize); |
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223 return KErrNotFound; |
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224 } |
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225 |
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226 |