src/cobalt/media/formats/mpeg/mpeg1_audio_stream_parser.cc

// 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 "cobalt/media/formats/mpeg/mpeg1_audio_stream_parser.h"

#include "cobalt/media/base/media_log.h"

namespace cobalt {
namespace media {

static const uint32_t kMPEG1StartCodeMask = 0xffe00000;

// Map that determines which bitrate_index & channel_mode combinations
// are allowed.
// Derived from: http://mpgedit.org/mpgedit/mpeg_format/MP3Format.html
static const bool kIsAllowed[17][4] = {
    {true, true, true, true},     // free
    {true, false, false, false},  // 32
    {true, false, false, false},  // 48
    {true, false, false, false},  // 56
    {true, true, true, true},     // 64
    {true, false, false, false},  // 80
    {true, true, true, true},     // 96
    {true, true, true, true},     // 112
    {true, true, true, true},     // 128
    {true, true, true, true},     // 160
    {true, true, true, true},     // 192
    {false, true, true, true},    // 224
    {false, true, true, true},    // 256
    {false, true, true, true},    // 320
    {false, true, true, true},    // 384
    {false, false, false, false}  // bad
};

// 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
static const 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
static const 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
static const 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.
static const int kXingHeaderMap[2][2] = {{32, 17}, {17, 9}};

// Frame header field constants.
static const int kBitrateFree = 0;
static const int kBitrateBad = 0xf;
static const int kSampleRateReserved = 3;
static const int kCodecDelay = 529;

// static
bool MPEG1AudioStreamParser::ParseHeader(
    const scoped_refptr<MediaLog>& media_log, 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) {
    MEDIA_LOG(ERROR, media_log)
        << "Invalid 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;
  }

  if (layer == kLayer2 && kIsAllowed[bitrate_index][channel_mode]) {
    MEDIA_LOG(ERROR, media_log) << "Invalid (bitrate_index, channel_mode)"
                                << " combination :" << std::hex
                                << " bitrate_index " << bitrate_index
                                << " channel_mode " << channel_mode;
    return false;
  }

  int bitrate = kBitrateMap[bitrate_index][kVersionLayerMap[version][layer]];

  if (bitrate == 0) {
    MEDIA_LOG(ERROR, media_log) << "Invalid 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) {
    MEDIA_LOG(ERROR, media_log) << "Invalid sample rate :" << std::hex
                                << " version " << version
                                << " sample_rate_index " << sample_rate_index;
    return false;
  }
  header->sample_rate = frame_sample_rate;

  // 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;
  }
  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(
    DecoderBuffer::Allocator* buffer_allocator)
    : MPEGAudioStreamParserBase(buffer_allocator, kMPEG1StartCodeMask,
                                kCodecMP3, kCodecDelay) {}

MPEG1AudioStreamParser::~MPEG1AudioStreamParser() {}

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) const {
  DCHECK(data);
  DCHECK_GE(size, 0);
  DCHECK(frame_size);

  if (size < kHeaderSize) return 0;

  Header header;
  if (!ParseHeader(media_log(), 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
}  // namespace cobalt