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/mpeg1_audio_stream_parser.h" 6 7 namespace media { 8 9 static const uint32 kMPEG1StartCodeMask = 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 kBitrateFree = 0; 84 static const int kBitrateBad = 0xf; 85 static const int kSampleRateReserved = 3; 86 static const int kCodecDelay = 529; 87 88 // static 89 bool MPEG1AudioStreamParser::ParseHeader( 90 const LogCB& log_cb, 91 const uint8* data, 92 Header* header) { 93 BitReader reader(data, kHeaderSize); 94 int sync; 95 int version; 96 int layer; 97 int is_protected; 98 int bitrate_index; 99 int sample_rate_index; 100 int has_padding; 101 int is_private; 102 int channel_mode; 103 int other_flags; 104 105 if (!reader.ReadBits(11, &sync) || 106 !reader.ReadBits(2, &version) || 107 !reader.ReadBits(2, &layer) || 108 !reader.ReadBits(1, &is_protected) || 109 !reader.ReadBits(4, &bitrate_index) || 110 !reader.ReadBits(2, &sample_rate_index) || 111 !reader.ReadBits(1, &has_padding) || 112 !reader.ReadBits(1, &is_private) || 113 !reader.ReadBits(2, &channel_mode) || 114 !reader.ReadBits(6, &other_flags)) { 115 return false; 116 } 117 118 DVLOG(2) << "Header data :" << std::hex 119 << " sync 0x" << sync 120 << " version 0x" << version 121 << " layer 0x" << layer 122 << " bitrate_index 0x" << bitrate_index 123 << " sample_rate_index 0x" << sample_rate_index 124 << " channel_mode 0x" << channel_mode; 125 126 if (sync != 0x7ff || 127 version == kVersionReserved || 128 layer == kLayerReserved || 129 bitrate_index == kBitrateFree || bitrate_index == kBitrateBad || 130 sample_rate_index == kSampleRateReserved) { 131 MEDIA_LOG(log_cb) << "Invalid header data :" << std::hex 132 << " sync 0x" << sync 133 << " version 0x" << version 134 << " layer 0x" << layer 135 << " bitrate_index 0x" << bitrate_index 136 << " sample_rate_index 0x" << sample_rate_index 137 << " channel_mode 0x" << channel_mode; 138 return false; 139 } 140 141 if (layer == kLayer2 && kIsAllowed[bitrate_index][channel_mode]) { 142 MEDIA_LOG(log_cb) << "Invalid (bitrate_index, channel_mode) combination :" 143 << std::hex 144 << " bitrate_index " << bitrate_index 145 << " channel_mode " << channel_mode; 146 return false; 147 } 148 149 int bitrate = kBitrateMap[bitrate_index][kVersionLayerMap[version][layer]]; 150 151 if (bitrate == 0) { 152 MEDIA_LOG(log_cb) << "Invalid bitrate :" << std::hex 153 << " version " << version 154 << " layer " << layer 155 << " bitrate_index " << bitrate_index; 156 return false; 157 } 158 159 DVLOG(2) << " bitrate " << bitrate; 160 161 int frame_sample_rate = kSampleRateMap[sample_rate_index][version]; 162 if (frame_sample_rate == 0) { 163 MEDIA_LOG(log_cb) << "Invalid sample rate :" << std::hex 164 << " version " << version 165 << " sample_rate_index " << sample_rate_index; 166 return false; 167 } 168 header->sample_rate = frame_sample_rate; 169 170 // http://teslabs.com/openplayer/docs/docs/specs/mp3_structure2.pdf 171 // Table 2.1.5 172 int samples_per_frame; 173 switch (layer) { 174 case kLayer1: 175 samples_per_frame = 384; 176 break; 177 178 case kLayer2: 179 samples_per_frame = 1152; 180 break; 181 182 case kLayer3: 183 if (version == kVersion2 || version == kVersion2_5) 184 samples_per_frame = 576; 185 else 186 samples_per_frame = 1152; 187 break; 188 189 default: 190 return false; 191 } 192 header->sample_count = samples_per_frame; 193 194 // http://teslabs.com/openplayer/docs/docs/specs/mp3_structure2.pdf 195 // Text just below Table 2.1.5. 196 if (layer == kLayer1) { 197 // This formulation is a slight variation on the equation below, 198 // but has slightly different truncation characteristics to deal 199 // with the fact that Layer 1 has 4 byte "slots" instead of single 200 // byte ones. 201 header->frame_size = 4 * (12 * bitrate * 1000 / frame_sample_rate); 202 } else { 203 header->frame_size = 204 ((samples_per_frame / 8) * bitrate * 1000) / frame_sample_rate; 205 } 206 207 if (has_padding) 208 header->frame_size += (layer == kLayer1) ? 4 : 1; 209 210 // Map Stereo(0), Joint Stereo(1), and Dual Channel (2) to 211 // CHANNEL_LAYOUT_STEREO and Single Channel (3) to CHANNEL_LAYOUT_MONO. 212 header->channel_layout = 213 (channel_mode == 3) ? CHANNEL_LAYOUT_MONO : CHANNEL_LAYOUT_STEREO; 214 215 header->version = static_cast<Version>(version); 216 header->layer = static_cast<Layer>(layer); 217 header->channel_mode = channel_mode; 218 return true; 219 } 220 221 222 MPEG1AudioStreamParser::MPEG1AudioStreamParser() 223 : MPEGAudioStreamParserBase(kMPEG1StartCodeMask, kCodecMP3, kCodecDelay) {} 224 225 MPEG1AudioStreamParser::~MPEG1AudioStreamParser() {} 226 227 int MPEG1AudioStreamParser::ParseFrameHeader(const uint8* data, 228 int size, 229 int* frame_size, 230 int* sample_rate, 231 ChannelLayout* channel_layout, 232 int* sample_count, 233 bool* metadata_frame) const { 234 DCHECK(data); 235 DCHECK_GE(size, 0); 236 DCHECK(frame_size); 237 238 if (size < kHeaderSize) 239 return 0; 240 241 Header header; 242 if (!ParseHeader(log_cb(), data, &header)) 243 return -1; 244 245 *frame_size = header.frame_size; 246 if (sample_rate) 247 *sample_rate = header.sample_rate; 248 if (sample_count) 249 *sample_count = header.sample_count; 250 if (channel_layout) 251 *channel_layout = header.channel_layout; 252 if (metadata_frame) 253 *metadata_frame = false; 254 255 const int header_bytes_read = kHeaderSize; 256 if (header.layer != kLayer3) 257 return header_bytes_read; 258 259 // Check if this is a XING frame and tell the base parser to skip it if so. 260 const int xing_header_index = 261 kXingHeaderMap[header.version == kVersion2 || 262 header.version == kVersion2_5][header.channel_mode == 3]; 263 uint32_t tag = 0; 264 265 // It's not a XING frame if the frame isn't big enough to be one. 266 if (*frame_size < 267 header_bytes_read + xing_header_index + static_cast<int>(sizeof(tag))) { 268 return header_bytes_read; 269 } 270 271 // If we don't have enough data available to check, return 0 so frame parsing 272 // will be retried once more data is available. 273 BitReader reader(data + header_bytes_read, size - header_bytes_read); 274 if (!reader.SkipBits(xing_header_index * 8) || 275 !reader.ReadBits(sizeof(tag) * 8, &tag)) { 276 return 0; 277 } 278 279 // Check to see if the tag contains 'Xing' or 'Info' 280 if (tag == 0x496e666f || tag == 0x58696e67) { 281 MEDIA_LOG(log_cb()) << "Skipping XING header."; 282 if (metadata_frame) 283 *metadata_frame = true; 284 return header_bytes_read + reader.bits_read() / 8; 285 } 286 287 // If it wasn't a XING frame, just return the number consumed bytes. 288 return header_bytes_read; 289 } 290 291 } // namespace media 292
