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- // Copyright 2014 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #include "media/formats/mpeg/mpeg1_audio_stream_parser.h"
- #include "media/base/media_log.h"
- namespace media {
- namespace {
- constexpr uint32_t kMPEG1StartCodeMask = 0xffe00000;
- // Maps version and layer information in the frame header
- // into an index for the |kBitrateMap|.
- // Derived from: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html
- constexpr int kVersionLayerMap[4][4] = {
- // { reserved, L3, L2, L1 }
- {5, 4, 4, 3}, // MPEG 2.5
- {5, 5, 5, 5}, // reserved
- {5, 4, 4, 3}, // MPEG 2
- {5, 2, 1, 0} // MPEG 1
- };
- // Maps the bitrate index field in the header and an index
- // from |kVersionLayerMap| to a frame bitrate.
- // Derived from: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html
- constexpr int kBitrateMap[16][6] = {
- // { V1L1, V1L2, V1L3, V2L1, V2L2 & V2L3, reserved }
- {0, 0, 0, 0, 0, 0}, {32, 32, 32, 32, 8, 0},
- {64, 48, 40, 48, 16, 0}, {96, 56, 48, 56, 24, 0},
- {128, 64, 56, 64, 32, 0}, {160, 80, 64, 80, 40, 0},
- {192, 96, 80, 96, 48, 0}, {224, 112, 96, 112, 56, 0},
- {256, 128, 112, 128, 64, 0}, {288, 160, 128, 144, 80, 0},
- {320, 192, 160, 160, 96, 0}, {352, 224, 192, 176, 112, 0},
- {384, 256, 224, 192, 128, 0}, {416, 320, 256, 224, 144, 0},
- {448, 384, 320, 256, 160, 0}, {0, 0, 0, 0, 0}};
- // Maps the sample rate index and version fields from the frame header
- // to a sample rate.
- // Derived from: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html
- constexpr int kSampleRateMap[4][4] = {
- // { V2.5, reserved, V2, V1 }
- {11025, 0, 22050, 44100},
- {12000, 0, 24000, 48000},
- {8000, 0, 16000, 32000},
- {0, 0, 0, 0}};
- // Offset in bytes from the end of the MP3 header to "Xing" or "Info" tags which
- // indicate a frame is silent metadata frame. Values taken from FFmpeg.
- constexpr int kXingHeaderMap[2][2] = {{32, 17}, {17, 9}};
- // Frame header field constants.
- constexpr int kBitrateFree = 0;
- constexpr int kBitrateBad = 0xf;
- constexpr int kSampleRateReserved = 3;
- constexpr int kCodecDelay = 529;
- } // namespace
- // static
- bool MPEG1AudioStreamParser::ParseHeader(MediaLog* media_log,
- size_t* media_log_limit,
- const uint8_t* data,
- Header* header) {
- BitReader reader(data, kHeaderSize);
- int sync;
- int version;
- int layer;
- int is_protected;
- int bitrate_index;
- int sample_rate_index;
- int has_padding;
- int is_private;
- int channel_mode;
- int other_flags;
- if (!reader.ReadBits(11, &sync) || !reader.ReadBits(2, &version) ||
- !reader.ReadBits(2, &layer) || !reader.ReadBits(1, &is_protected) ||
- !reader.ReadBits(4, &bitrate_index) ||
- !reader.ReadBits(2, &sample_rate_index) ||
- !reader.ReadBits(1, &has_padding) || !reader.ReadBits(1, &is_private) ||
- !reader.ReadBits(2, &channel_mode) || !reader.ReadBits(6, &other_flags)) {
- return false;
- }
- DVLOG(2) << "Header data :" << std::hex << " sync 0x" << sync << " version 0x"
- << version << " layer 0x" << layer << " bitrate_index 0x"
- << bitrate_index << " sample_rate_index 0x" << sample_rate_index
- << " channel_mode 0x" << channel_mode;
- if (sync != 0x7ff || version == kVersionReserved || layer == kLayerReserved ||
- bitrate_index == kBitrateFree || bitrate_index == kBitrateBad ||
- sample_rate_index == kSampleRateReserved) {
- if (media_log) {
- LIMITED_MEDIA_LOG(DEBUG, media_log, *media_log_limit, 5)
- << "Invalid MP3 header data :" << std::hex << " sync 0x" << sync
- << " version 0x" << version << " layer 0x" << layer
- << " bitrate_index 0x" << bitrate_index << " sample_rate_index 0x"
- << sample_rate_index << " channel_mode 0x" << channel_mode;
- }
- return false;
- }
- // Note: For MPEG2 we don't check if a given bitrate or channel layout is
- // allowed per spec since all tested decoders don't seem to care.
- int bitrate = kBitrateMap[bitrate_index][kVersionLayerMap[version][layer]];
- if (bitrate == 0) {
- if (media_log) {
- LIMITED_MEDIA_LOG(DEBUG, media_log, *media_log_limit, 5)
- << "Invalid MP3 bitrate :" << std::hex << " version " << version
- << " layer " << layer << " bitrate_index " << bitrate_index;
- }
- return false;
- }
- DVLOG(2) << " bitrate " << bitrate;
- int frame_sample_rate = kSampleRateMap[sample_rate_index][version];
- if (frame_sample_rate == 0) {
- if (media_log) {
- LIMITED_MEDIA_LOG(DEBUG, media_log, *media_log_limit, 5)
- << "Invalid MP3 sample rate :" << std::hex << " version " << version
- << " sample_rate_index " << sample_rate_index;
- }
- return false;
- }
- // http://teslabs.com/openplayer/docs/docs/specs/mp3_structure2.pdf
- // Table 2.1.5
- int samples_per_frame;
- switch (layer) {
- case kLayer1:
- samples_per_frame = 384;
- break;
- case kLayer2:
- samples_per_frame = 1152;
- break;
- case kLayer3:
- if (version == kVersion2 || version == kVersion2_5) {
- samples_per_frame = 576;
- } else {
- samples_per_frame = 1152;
- }
- break;
- default:
- return false;
- }
- if (!header)
- return true;
- header->sample_rate = frame_sample_rate;
- header->sample_count = samples_per_frame;
- // http://teslabs.com/openplayer/docs/docs/specs/mp3_structure2.pdf
- // Text just below Table 2.1.5.
- if (layer == kLayer1) {
- // This formulation is a slight variation on the equation below,
- // but has slightly different truncation characteristics to deal
- // with the fact that Layer 1 has 4 byte "slots" instead of single
- // byte ones.
- header->frame_size = 4 * (12 * bitrate * 1000 / frame_sample_rate);
- } else {
- header->frame_size =
- ((samples_per_frame / 8) * bitrate * 1000) / frame_sample_rate;
- }
- if (has_padding)
- header->frame_size += (layer == kLayer1) ? 4 : 1;
- // Map Stereo(0), Joint Stereo(1), and Dual Channel (2) to
- // CHANNEL_LAYOUT_STEREO and Single Channel (3) to CHANNEL_LAYOUT_MONO.
- header->channel_layout =
- (channel_mode == 3) ? CHANNEL_LAYOUT_MONO : CHANNEL_LAYOUT_STEREO;
- header->version = static_cast<Version>(version);
- header->layer = static_cast<Layer>(layer);
- header->channel_mode = channel_mode;
- return true;
- }
- MPEG1AudioStreamParser::MPEG1AudioStreamParser()
- : MPEGAudioStreamParserBase(kMPEG1StartCodeMask,
- AudioCodec::kMP3,
- kCodecDelay) {}
- MPEG1AudioStreamParser::~MPEG1AudioStreamParser() = default;
- int MPEG1AudioStreamParser::ParseFrameHeader(const uint8_t* data,
- int size,
- int* frame_size,
- int* sample_rate,
- ChannelLayout* channel_layout,
- int* sample_count,
- bool* metadata_frame,
- std::vector<uint8_t>* extra_data) {
- DCHECK(data);
- DCHECK_GE(size, 0);
- DCHECK(frame_size);
- if (size < kHeaderSize)
- return 0;
- Header header;
- if (!ParseHeader(media_log(), &mp3_parse_error_limit_, data, &header))
- return -1;
- *frame_size = header.frame_size;
- if (sample_rate)
- *sample_rate = header.sample_rate;
- if (sample_count)
- *sample_count = header.sample_count;
- if (channel_layout)
- *channel_layout = header.channel_layout;
- if (metadata_frame)
- *metadata_frame = false;
- const int header_bytes_read = kHeaderSize;
- if (header.layer != kLayer3)
- return header_bytes_read;
- // Check if this is a XING frame and tell the base parser to skip it if so.
- const int xing_header_index =
- kXingHeaderMap[header.version == kVersion2 ||
- header.version == kVersion2_5][header.channel_mode == 3];
- uint32_t tag = 0;
- // It's not a XING frame if the frame isn't big enough to be one.
- if (*frame_size <
- header_bytes_read + xing_header_index + static_cast<int>(sizeof(tag))) {
- return header_bytes_read;
- }
- // If we don't have enough data available to check, return 0 so frame parsing
- // will be retried once more data is available.
- BitReader reader(data + header_bytes_read, size - header_bytes_read);
- if (!reader.SkipBits(xing_header_index * 8) ||
- !reader.ReadBits(sizeof(tag) * 8, &tag)) {
- return 0;
- }
- // Check to see if the tag contains 'Xing' or 'Info'
- if (tag == 0x496e666f || tag == 0x58696e67) {
- MEDIA_LOG(DEBUG, media_log()) << "Skipping XING header.";
- if (metadata_frame)
- *metadata_frame = true;
- return header_bytes_read + reader.bits_read() / 8;
- }
- // If it wasn't a XING frame, just return the number consumed bytes.
- return header_bytes_read;
- }
- } // namespace media
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