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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"
namespace media {
static const uint32 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 LogCB& log_cb,
const uint8* 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, log_cb)
<< "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, log_cb) << "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, log_cb) << "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, log_cb) << "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()
: MPEGAudioStreamParserBase(kMPEG1StartCodeMask, kCodecMP3, kCodecDelay) {}
MPEG1AudioStreamParser::~MPEG1AudioStreamParser() {}
int MPEG1AudioStreamParser::ParseFrameHeader(const uint8* data,
int size,
int* frame_size,
int* sample_rate,
ChannelLayout* channel_layout,
int* sample_count,
bool* metadata_frame) const {
DCHECK(data);
DCHECK_GE(size, 0);
DCHECK(frame_size);
if (size < kHeaderSize)
return 0;
Header header;
if (!ParseHeader(log_cb(), 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, log_cb()) << "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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