1 // Copyright 2014 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #include "media/formats/mpeg/mp3_stream_parser.h" 6 7 namespace media { 8 9 static const uint32 kMP3StartCodeMask = 0xffe00000; 10 11 // Map that determines which bitrate_index & channel_mode combinations 12 // are allowed. 13 // Derived from: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html 14 static const bool kIsAllowed[17][4] = { 15 { true, true, true, true }, // free 16 { true, false, false, false }, // 32 17 { true, false, false, false }, // 48 18 { true, false, false, false }, // 56 19 { true, true, true, true }, // 64 20 { true, false, false, false }, // 80 21 { true, true, true, true }, // 96 22 { true, true, true, true }, // 112 23 { true, true, true, true }, // 128 24 { true, true, true, true }, // 160 25 { true, true, true, true }, // 192 26 { false, true, true, true }, // 224 27 { false, true, true, true }, // 256 28 { false, true, true, true }, // 320 29 { false, true, true, true }, // 384 30 { false, false, false, false } // bad 31 }; 32 33 // Maps version and layer information in the frame header 34 // into an index for the |kBitrateMap|. 35 // Derived from: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html 36 static const int kVersionLayerMap[4][4] = { 37 // { reserved, L3, L2, L1 } 38 { 5, 4, 4, 3 }, // MPEG 2.5 39 { 5, 5, 5, 5 }, // reserved 40 { 5, 4, 4, 3 }, // MPEG 2 41 { 5, 2, 1, 0 } // MPEG 1 42 }; 43 44 // Maps the bitrate index field in the header and an index 45 // from |kVersionLayerMap| to a frame bitrate. 46 // Derived from: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html 47 static const int kBitrateMap[16][6] = { 48 // { V1L1, V1L2, V1L3, V2L1, V2L2 & V2L3, reserved } 49 { 0, 0, 0, 0, 0, 0 }, 50 { 32, 32, 32, 32, 8, 0 }, 51 { 64, 48, 40, 48, 16, 0 }, 52 { 96, 56, 48, 56, 24, 0 }, 53 { 128, 64, 56, 64, 32, 0 }, 54 { 160, 80, 64, 80, 40, 0 }, 55 { 192, 96, 80, 96, 48, 0 }, 56 { 224, 112, 96, 112, 56, 0 }, 57 { 256, 128, 112, 128, 64, 0 }, 58 { 288, 160, 128, 144, 80, 0 }, 59 { 320, 192, 160, 160, 96, 0 }, 60 { 352, 224, 192, 176, 112, 0 }, 61 { 384, 256, 224, 192, 128, 0 }, 62 { 416, 320, 256, 224, 144, 0 }, 63 { 448, 384, 320, 256, 160, 0 }, 64 { 0, 0, 0, 0, 0} 65 }; 66 67 // Maps the sample rate index and version fields from the frame header 68 // to a sample rate. 69 // Derived from: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html 70 static const int kSampleRateMap[4][4] = { 71 // { V2.5, reserved, V2, V1 } 72 { 11025, 0, 22050, 44100 }, 73 { 12000, 0, 24000, 48000 }, 74 { 8000, 0, 16000, 32000 }, 75 { 0, 0, 0, 0 } 76 }; 77 78 // Offset in bytes from the end of the MP3 header to "Xing" or "Info" tags which 79 // indicate a frame is silent metadata frame. Values taken from FFmpeg. 80 static const int kXingHeaderMap[2][2] = {{32, 17}, {17, 9}}; 81 82 // Frame header field constants. 83 static const int kVersion2 = 2; 84 static const int kVersionReserved = 1; 85 static const int kVersion2_5 = 0; 86 static const int kLayerReserved = 0; 87 static const int kLayer1 = 3; 88 static const int kLayer2 = 2; 89 static const int kLayer3 = 1; 90 static const int kBitrateFree = 0; 91 static const int kBitrateBad = 0xf; 92 static const int kSampleRateReserved = 3; 93 static const int kCodecDelay = 529; 94 95 MP3StreamParser::MP3StreamParser() 96 : MPEGAudioStreamParserBase(kMP3StartCodeMask, kCodecMP3, kCodecDelay) {} 97 98 MP3StreamParser::~MP3StreamParser() {} 99 100 int MP3StreamParser::ParseFrameHeader(const uint8* data, 101 int size, 102 int* frame_size, 103 int* sample_rate, 104 ChannelLayout* channel_layout, 105 int* sample_count, 106 bool* metadata_frame) const { 107 DCHECK(data); 108 DCHECK_GE(size, 0); 109 DCHECK(frame_size); 110 111 if (size < 4) 112 return 0; 113 114 BitReader reader(data, size); 115 int sync; 116 int version; 117 int layer; 118 int is_protected; 119 int bitrate_index; 120 int sample_rate_index; 121 int has_padding; 122 int is_private; 123 int channel_mode; 124 int other_flags; 125 126 if (!reader.ReadBits(11, &sync) || 127 !reader.ReadBits(2, &version) || 128 !reader.ReadBits(2, &layer) || 129 !reader.ReadBits(1, &is_protected) || 130 !reader.ReadBits(4, &bitrate_index) || 131 !reader.ReadBits(2, &sample_rate_index) || 132 !reader.ReadBits(1, &has_padding) || 133 !reader.ReadBits(1, &is_private) || 134 !reader.ReadBits(2, &channel_mode) || 135 !reader.ReadBits(6, &other_flags)) { 136 return -1; 137 } 138 139 DVLOG(2) << "Header data :" << std::hex 140 << " sync 0x" << sync 141 << " version 0x" << version 142 << " layer 0x" << layer 143 << " bitrate_index 0x" << bitrate_index 144 << " sample_rate_index 0x" << sample_rate_index 145 << " channel_mode 0x" << channel_mode; 146 147 if (sync != 0x7ff || 148 version == kVersionReserved || 149 layer == kLayerReserved || 150 bitrate_index == kBitrateFree || bitrate_index == kBitrateBad || 151 sample_rate_index == kSampleRateReserved) { 152 MEDIA_LOG(log_cb()) << "Invalid header data :" << std::hex 153 << " sync 0x" << sync 154 << " version 0x" << version 155 << " layer 0x" << layer 156 << " bitrate_index 0x" << bitrate_index 157 << " sample_rate_index 0x" << sample_rate_index 158 << " channel_mode 0x" << channel_mode; 159 return -1; 160 } 161 162 if (layer == kLayer2 && kIsAllowed[bitrate_index][channel_mode]) { 163 MEDIA_LOG(log_cb()) << "Invalid (bitrate_index, channel_mode) combination :" 164 << std::hex 165 << " bitrate_index " << bitrate_index 166 << " channel_mode " << channel_mode; 167 return -1; 168 } 169 170 int bitrate = kBitrateMap[bitrate_index][kVersionLayerMap[version][layer]]; 171 172 if (bitrate == 0) { 173 MEDIA_LOG(log_cb()) << "Invalid bitrate :" << std::hex 174 << " version " << version 175 << " layer " << layer 176 << " bitrate_index " << bitrate_index; 177 return -1; 178 } 179 180 DVLOG(2) << " bitrate " << bitrate; 181 182 int frame_sample_rate = kSampleRateMap[sample_rate_index][version]; 183 if (frame_sample_rate == 0) { 184 MEDIA_LOG(log_cb()) << "Invalid sample rate :" << std::hex 185 << " version " << version 186 << " sample_rate_index " << sample_rate_index; 187 return -1; 188 } 189 190 if (sample_rate) 191 *sample_rate = frame_sample_rate; 192 193 // http://teslabs.com/openplayer/docs/docs/specs/mp3_structure2.pdf 194 // Table 2.1.5 195 int samples_per_frame; 196 switch (layer) { 197 case kLayer1: 198 samples_per_frame = 384; 199 break; 200 201 case kLayer2: 202 samples_per_frame = 1152; 203 break; 204 205 case kLayer3: 206 if (version == kVersion2 || version == kVersion2_5) 207 samples_per_frame = 576; 208 else 209 samples_per_frame = 1152; 210 break; 211 212 default: 213 return -1; 214 } 215 216 if (sample_count) 217 *sample_count = samples_per_frame; 218 219 // http://teslabs.com/openplayer/docs/docs/specs/mp3_structure2.pdf 220 // Text just below Table 2.1.5. 221 if (layer == kLayer1) { 222 // This formulation is a slight variation on the equation below, 223 // but has slightly different truncation characteristics to deal 224 // with the fact that Layer 1 has 4 byte "slots" instead of single 225 // byte ones. 226 *frame_size = 4 * (12 * bitrate * 1000 / frame_sample_rate); 227 } else { 228 *frame_size = 229 ((samples_per_frame / 8) * bitrate * 1000) / frame_sample_rate; 230 } 231 232 if (has_padding) 233 *frame_size += (layer == kLayer1) ? 4 : 1; 234 235 if (channel_layout) { 236 // Map Stereo(0), Joint Stereo(1), and Dual Channel (2) to 237 // CHANNEL_LAYOUT_STEREO and Single Channel (3) to CHANNEL_LAYOUT_MONO. 238 *channel_layout = 239 (channel_mode == 3) ? CHANNEL_LAYOUT_MONO : CHANNEL_LAYOUT_STEREO; 240 } 241 242 if (metadata_frame) 243 *metadata_frame = false; 244 245 const int header_bytes_read = reader.bits_read() / 8; 246 if (layer != kLayer3) 247 return header_bytes_read; 248 249 // Check if this is a XING frame and tell the base parser to skip it if so. 250 const int xing_header_index = 251 kXingHeaderMap[version == kVersion2 || 252 version == kVersion2_5][channel_mode == 3]; 253 uint32_t tag = 0; 254 255 // It's not a XING frame if the frame isn't big enough to be one. 256 if (*frame_size < 257 header_bytes_read + xing_header_index + static_cast<int>(sizeof(tag))) { 258 return header_bytes_read; 259 } 260 261 // If we don't have enough data available to check, return 0 so frame parsing 262 // will be retried once more data is available. 263 if (!reader.SkipBits(xing_header_index * 8) || 264 !reader.ReadBits(sizeof(tag) * 8, &tag)) { 265 return 0; 266 } 267 268 // Check to see if the tag contains 'Xing' or 'Info' 269 if (tag == 0x496e666f || tag == 0x58696e67) { 270 MEDIA_LOG(log_cb()) << "Skipping XING header."; 271 if (metadata_frame) 272 *metadata_frame = true; 273 return reader.bits_read() / 8; 274 } 275 276 // If it wasn't a XING frame, just return the number consumed bytes. 277 return header_bytes_read; 278 } 279 280 } // namespace media 281
