/*
* Copyright (c) 2021, Arne Elster <arne@elster.li>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include "MP3Loader.h"
#include "MP3HuffmanTables.h"
#include "MP3Tables.h"
#include "MP3Types.h"
#include <AK/Endian.h>
#include <AK/FixedArray.h>
#include <LibCore/File.h>
namespace Audio {
DSP::MDCT<12> MP3LoaderPlugin::s_mdct_12;
DSP::MDCT<36> MP3LoaderPlugin::s_mdct_36;
MP3LoaderPlugin::MP3LoaderPlugin(NonnullOwnPtr<SeekableStream> stream)
: LoaderPlugin(move(stream))
{
}
MaybeLoaderError MP3LoaderPlugin::skip_id3(SeekableStream& stream)
{
// FIXME: This is a bit of a hack until we have a proper ID3 reader and MP3 demuxer.
// Based on https://mutagen-specs.readthedocs.io/en/latest/id3/id3v2.2.html
char identifier_buffer[3] = { 0, 0, 0 };
auto read_identifier = StringView(TRY(stream.read_some({ &identifier_buffer[0], sizeof(identifier_buffer) })));
if (read_identifier == "ID3"sv) {
[[maybe_unused]] auto version = TRY(stream.read_value<u8>());
[[maybe_unused]] auto revision = TRY(stream.read_value<u8>());
[[maybe_unused]] auto flags = TRY(stream.read_value<u8>());
auto size = 0;
for (auto i = 0; i < 4; i++) {
// Each byte has a zeroed most significant bit to prevent it from looking like a sync code.
auto byte = TRY(stream.read_value<u8>());
size <<= 7;
size |= byte & 0x7F;
}
TRY(stream.seek(size, SeekMode::FromCurrentPosition));
} else if (read_identifier != "TAG"sv) {
MUST(stream.seek(-static_cast<int>(read_identifier.length()), SeekMode::FromCurrentPosition));
}
return {};
}
bool MP3LoaderPlugin::sniff(SeekableStream& stream)
{
auto skip_id3_result = skip_id3(stream);
if (skip_id3_result.is_error())
return false;
return !synchronize_and_read_header(stream, 0).is_error();
}
ErrorOr<NonnullOwnPtr<LoaderPlugin>, LoaderError> MP3LoaderPlugin::create(NonnullOwnPtr<SeekableStream> stream)
{
auto loader = make<MP3LoaderPlugin>(move(stream));
TRY(loader->initialize());
return loader;
}
MaybeLoaderError MP3LoaderPlugin::initialize()
{
TRY(build_seek_table());
TRY(seek(0));
auto header = TRY(synchronize_and_read_header());
m_sample_rate = header.samplerate;
m_num_channels = header.channel_count();
m_loaded_samples = 0;
TRY(seek(0));
return {};
}
MaybeLoaderError MP3LoaderPlugin::reset()
{
TRY(seek(0));
m_synthesis_buffer = {};
m_loaded_samples = 0;
TRY(m_bit_reservoir.discard(m_bit_reservoir.used_buffer_size()));
return {};
}
MaybeLoaderError MP3LoaderPlugin::seek(int const position)
{
auto seek_entry = m_seek_table.seek_point_before(position);
if (seek_entry.has_value()) {
TRY(m_stream->seek(seek_entry->byte_offset, SeekMode::SetPosition));
m_loaded_samples = seek_entry->sample_index;
}
m_synthesis_buffer = {};
TRY(m_bit_reservoir.discard(m_bit_reservoir.used_buffer_size()));
return {};
}
ErrorOr<Vector<FixedArray<Sample>>, LoaderError> MP3LoaderPlugin::load_chunks(size_t samples_to_read_from_input)
{
int samples_to_read = samples_to_read_from_input;
Vector<FixedArray<Sample>> frames;
while (samples_to_read > 0) {
FixedArray<Sample> samples = TRY(FixedArray<Sample>::create(MP3::frame_size));
auto maybe_frame = read_next_frame();
if (maybe_frame.is_error()) {
if (m_stream->is_eof())
return Vector<FixedArray<Sample>> {};
return maybe_frame.release_error();
}
auto frame = maybe_frame.release_value();
bool const is_stereo = frame.header.channel_count() == 2;
size_t current_frame_read = 0;
for (; current_frame_read < MP3::granule_size; current_frame_read++) {
auto const left_sample = frame.channels[0].granules[0].pcm[current_frame_read / 32][current_frame_read % 32];
auto const right_sample = is_stereo ? frame.channels[1].granules[0].pcm[current_frame_read / 32][current_frame_read % 32] : left_sample;
samples[current_frame_read] = Sample { left_sample, right_sample };
samples_to_read--;
}
for (; current_frame_read < MP3::frame_size; current_frame_read++) {
auto const left_sample = frame.channels[0].granules[1].pcm[(current_frame_read - MP3::granule_size) / 32][(current_frame_read - MP3::granule_size) % 32];
auto const right_sample = is_stereo ? frame.channels[1].granules[1].pcm[(current_frame_read - MP3::granule_size) / 32][(current_frame_read - MP3::granule_size) % 32] : left_sample;
samples[current_frame_read] = Sample { left_sample, right_sample };
samples_to_read--;
}
m_loaded_samples += samples.size();
TRY(frames.try_append(move(samples)));
}
return frames;
}
MaybeLoaderError MP3LoaderPlugin::build_seek_table()
{
VERIFY(MUST(m_stream->tell()) == 0);
TRY(skip_id3(*m_stream));
int sample_count = 0;
size_t frame_count = 0;
m_seek_table = {};
while (true) {
auto error_or_header = synchronize_and_read_header();
if (error_or_header.is_error())
break;
if (frame_count % 10 == 0) {
auto frame_pos = TRY(m_stream->tell()) - error_or_header.value().header_size;
TRY(m_seek_table.insert_seek_point({ static_cast<u64>(sample_count), frame_pos }));
}
frame_count++;
sample_count += MP3::frame_size;
TRY(m_stream->seek(error_or_header.value().frame_size - error_or_header.value().header_size, SeekMode::FromCurrentPosition));
}
m_total_samples = sample_count;
return {};
}
ErrorOr<MP3::Header, LoaderError> MP3LoaderPlugin::read_header(SeekableStream& stream, size_t sample_index)
{
auto bitstream = BigEndianInputBitStream(MaybeOwned<Stream>(stream));
if (TRY(bitstream.read_bits(4)) != 0xF)
return LoaderError { LoaderError::Category::Format, sample_index, "Frame header did not start with sync code."_fly_string };
MP3::Header header;
header.id = TRY(bitstream.read_bit());
header.layer = MP3::Tables::LayerNumberLookup[TRY(bitstream.read_bits(2))];
if (header.layer <= 0)
return LoaderError { LoaderError::Category::Format, sample_index, "Frame header contains invalid layer number."_fly_string };
header.protection_bit = TRY(bitstream.read_bit());
header.bitrate = MP3::Tables::BitratesPerLayerLookup[header.layer - 1][TRY(bitstream.read_bits(4))];
if (header.bitrate <= 0)
return LoaderError { LoaderError::Category::Format, sample_index, "Frame header contains invalid bitrate."_fly_string };
header.samplerate = MP3::Tables::SampleratesLookup[TRY(bitstream.read_bits(2))];
if (header.samplerate <= 0)
return LoaderError { LoaderError::Category::Format, sample_index, "Frame header contains invalid samplerate."_fly_string };
header.padding_bit = TRY(bitstream.read_bit());
header.private_bit = TRY(bitstream.read_bit());
header.mode = static_cast<MP3::Mode>(TRY(bitstream.read_bits(2)));
header.mode_extension = static_cast<MP3::ModeExtension>(TRY(bitstream.read_bits(2)));
header.copyright_bit = TRY(bitstream.read_bit());
header.original_bit = TRY(bitstream.read_bit());
header.emphasis = static_cast<MP3::Emphasis>(TRY(bitstream.read_bits(2)));
header.header_size = 4;
if (!header.protection_bit) {
header.crc16 = TRY(bitstream.read_bits<u16>(16));
header.header_size += 2;
}
header.frame_size = 144 * header.bitrate * 1000 / header.samplerate + header.padding_bit;
header.slot_count = header.frame_size - ((header.channel_count() == 2 ? 32 : 17) + header.header_size);
return header;
}
ErrorOr<MP3::Header, LoaderError> MP3LoaderPlugin::synchronize_and_read_header(SeekableStream& stream, size_t sample_index)
{
while (!stream.is_eof()) {
bool last_was_all_set = false;
while (!stream.is_eof()) {
u8 byte = TRY(stream.read_value<u8>());
if (last_was_all_set && (byte & 0xF0) == 0xF0) {
// Seek back, since there is still data we have not consumed within the current byte.
// read_header() will consume and check these 4 bits itself and then continue reading
// the rest of the data from there.
TRY(stream.seek(-1, SeekMode::FromCurrentPosition));
break;
}
last_was_all_set = byte == 0xFF;
}
auto header_start = TRY(stream.tell());
auto header_result = read_header(stream, sample_index);
if (header_result.is_error() || header_result.value().id != 1 || header_result.value().layer != 3) {
TRY(stream.seek(header_start, SeekMode::SetPosition));
continue;
}
return header_result.value();
}
return LoaderError { LoaderError::Category::Format, sample_index, "Failed to synchronize."_fly_string };
}
ErrorOr<MP3::Header, LoaderError> MP3LoaderPlugin::synchronize_and_read_header()
{
return MP3LoaderPlugin::synchronize_and_read_header(*m_stream, m_loaded_samples);
}
ErrorOr<MP3::MP3Frame, LoaderError> MP3LoaderPlugin::read_next_frame()
{
return read_frame_data(TRY(synchronize_and_read_header()));
}
ErrorOr<MP3::MP3Frame, LoaderError> MP3LoaderPlugin::read_frame_data(MP3::Header const& header)
{
MP3::MP3Frame frame { header };
TRY(read_side_information(frame));
auto maybe_buffer = ByteBuffer::create_uninitialized(header.slot_count);
if (maybe_buffer.is_error())
return LoaderError { LoaderError::Category::IO, m_loaded_samples, "Out of memory"_fly_string };
auto& buffer = maybe_buffer.value();
size_t old_reservoir_size = m_bit_reservoir.used_buffer_size();
TRY(m_stream->read_until_filled(buffer));
TRY(m_bit_reservoir.write_until_depleted(buffer));
// If we don't have enough data in the reservoir to process this frame, skip it (but keep the data).
if (old_reservoir_size < static_cast<size_t>(frame.main_data_begin))
return frame;
TRY(m_bit_reservoir.discard(old_reservoir_size - frame.main_data_begin));
BigEndianInputBitStream reservoir_stream { MaybeOwned<Stream>(m_bit_reservoir) };
for (size_t granule_index = 0; granule_index < 2; granule_index++) {
for (size_t channel_index = 0; channel_index < header.channel_count(); channel_index++) {
size_t scale_factor_size = TRY(read_scale_factors(frame, reservoir_stream, granule_index, channel_index));
TRY(read_huffman_data(frame, reservoir_stream, granule_index, channel_index, scale_factor_size));
if (frame.channels[channel_index].granules[granule_index].block_type == MP3::BlockType::Short) {
reorder_samples(frame.channels[channel_index].granules[granule_index], frame.header.samplerate);
// Only reduce alias for lowest 2 bands as they're long.
// Afaik this is not mentioned in the ISO spec, but it is addressed in the
// changelog for the ISO compliance tests.
if (frame.channels[channel_index].granules[granule_index].mixed_block_flag)
reduce_alias(frame.channels[channel_index].granules[granule_index], 36);
} else {
reduce_alias(frame.channels[channel_index].granules[granule_index]);
}
}
if (header.mode == MP3::Mode::JointStereo) {
process_stereo(frame, granule_index);
}
}
for (size_t granule_index = 0; granule_index < 2; granule_index++) {
for (size_t channel_index = 0; channel_index < header.channel_count(); channel_index++) {
auto& granule = frame.channels[channel_index].granules[granule_index];
for (size_t i = 0; i < MP3::granule_size; i += 18) {
MP3::BlockType block_type = granule.block_type;
if (i < 36 && granule.mixed_block_flag) {
// ISO/IEC 11172-3: if mixed_block_flag is set, the lowest two subbands are transformed with normal window.
block_type = MP3::BlockType::Normal;
}
Array<float, 36> output;
transform_samples_to_time(granule.samples, i, output, block_type);
int const subband_index = i / 18;
for (size_t sample_index = 0; sample_index < 18; sample_index++) {
// overlap add
granule.filter_bank_input[subband_index][sample_index] = output[sample_index] + m_last_values[channel_index][subband_index][sample_index];
m_last_values[channel_index][subband_index][sample_index] = output[sample_index + 18];
// frequency inversion
if (subband_index % 2 == 1 && sample_index % 2 == 1)
granule.filter_bank_input[subband_index][sample_index] *= -1;
}
}
}
}
Array<float, 32> in_samples;
for (size_t channel_index = 0; channel_index < frame.header.channel_count(); channel_index++) {
for (size_t granule_index = 0; granule_index < 2; granule_index++) {
auto& granule = frame.channels[channel_index].granules[granule_index];
for (size_t sample_index = 0; sample_index < 18; sample_index++) {
for (size_t band_index = 0; band_index < 32; band_index++) {
in_samples[band_index] = granule.filter_bank_input[band_index][sample_index];
}
synthesis(m_synthesis_buffer[channel_index], in_samples, granule.pcm[sample_index]);
}
}
}
return frame;
}
MaybeLoaderError MP3LoaderPlugin::read_side_information(MP3::MP3Frame& frame)
{
auto bitstream = BigEndianInputBitStream(MaybeOwned<Stream>(*m_stream));
frame.main_data_begin = TRY(bitstream.read_bits(9));
if (frame.header.channel_count() == 1) {
frame.private_bits = TRY(bitstream.read_bits(5));
} else {
frame.private_bits = TRY(bitstream.read_bits(3));
}
for (size_t channel_index = 0; channel_index < frame.header.channel_count(); channel_index++) {
for (size_t scale_factor_selection_info_band = 0; scale_factor_selection_info_band < 4; scale_factor_selection_info_band++) {
frame.channels[channel_index].scale_factor_selection_info[scale_factor_selection_info_band] = TRY(bitstream.read_bit());
}
}
for (size_t granule_index = 0; granule_index < 2; granule_index++) {
for (size_t channel_index = 0; channel_index < frame.header.channel_count(); channel_index++) {
auto& granule = frame.channels[channel_index].granules[granule_index];
granule.part_2_3_length = TRY(bitstream.read_bits(12));
granule.big_values = TRY(bitstream.read_bits(9));
granule.global_gain = TRY(bitstream.read_bits(8));
granule.scalefac_compress = TRY(bitstream.read_bits(4));
granule.window_switching_flag = TRY(bitstream.read_bit());
if (granule.window_switching_flag) {
granule.block_type = static_cast<MP3::BlockType>(TRY(bitstream.read_bits(2)));
granule.mixed_block_flag = TRY(bitstream.read_bit());
for (size_t region = 0; region < 2; region++)
granule.table_select[region] = TRY(bitstream.read_bits(5));
for (size_t window = 0; window < 3; window++)
granule.sub_block_gain[window] = TRY(bitstream.read_bits(3));
granule.region0_count = (granule.block_type == MP3::BlockType::Short && !granule.mixed_block_flag) ? 8 : 7;
granule.region1_count = 36;
} else {
for (size_t region = 0; region < 3; region++)
granule.table_select[region] = TRY(bitstream.read_bits(5));
granule.region0_count = TRY(bitstream.read_bits(4));
granule.region1_count = TRY(bitstream.read_bits(3));
}
granule.preflag = TRY(bitstream.read_bit());
granule.scalefac_scale = TRY(bitstream.read_bit());
granule.count1table_select = TRY(bitstream.read_bit());
}
}
return {};
}
// From ISO/IEC 11172-3 (2.4.3.4.7.1)
Array<float, MP3::granule_size> MP3LoaderPlugin::calculate_frame_exponents(MP3::MP3Frame const& frame, size_t granule_index, size_t channel_index)
{
Array<float, MP3::granule_size> exponents;
auto fill_band = [&exponents](float exponent, size_t start, size_t end) {
for (size_t j = start; j <= end; j++) {
exponents[j] = exponent;
}
};
auto const& channel = frame.channels[channel_index];
auto const& granule = frame.channels[channel_index].granules[granule_index];
auto const scale_factor_bands = get_scalefactor_bands(granule, frame.header.samplerate);
float const scale_factor_multiplier = granule.scalefac_scale ? 1 : 0.5;
int const gain = granule.global_gain - 210;
if (granule.block_type != MP3::BlockType::Short) {
for (size_t band_index = 0; band_index < 22; band_index++) {
float const exponent = gain / 4.0f - (scale_factor_multiplier * (channel.scale_factors[band_index] + granule.preflag * MP3::Tables::Pretab[band_index]));
fill_band(AK::pow<float>(2.0, exponent), scale_factor_bands[band_index].start, scale_factor_bands[band_index].end);
}
} else {
size_t band_index = 0;
size_t sample_count = 0;
if (granule.mixed_block_flag) {
while (sample_count < 36) {
float const exponent = gain / 4.0f - (scale_factor_multiplier * (channel.scale_factors[band_index] + granule.preflag * MP3::Tables::Pretab[band_index]));
fill_band(AK::pow<float>(2.0, exponent), scale_factor_bands[band_index].start, scale_factor_bands[band_index].end);
sample_count += scale_factor_bands[band_index].width;
band_index++;
}
}
float const gain0 = (gain - 8 * granule.sub_block_gain[0]) / 4.0;
float const gain1 = (gain - 8 * granule.sub_block_gain[1]) / 4.0;
float const gain2 = (gain - 8 * granule.sub_block_gain[2]) / 4.0;
while (sample_count < MP3::granule_size && band_index < scale_factor_bands.size()) {
float const exponent0 = gain0 - (scale_factor_multiplier * channel.scale_factors[band_index + 0]);
float const exponent1 = gain1 - (scale_factor_multiplier * channel.scale_factors[band_index + 1]);
float const exponent2 = gain2 - (scale_factor_multiplier * channel.scale_factors[band_index + 2]);
fill_band(AK::pow<float>(2.0, exponent0), scale_factor_bands[band_index + 0].start, scale_factor_bands[band_index + 0].end);
sample_count += scale_factor_bands[band_index + 0].width;
fill_band(AK::pow<float>(2.0, exponent1), scale_factor_bands[band_index + 1].start, scale_factor_bands[band_index + 1].end);
sample_count += scale_factor_bands[band_index + 1].width;
fill_band(AK::pow<float>(2.0, exponent2), scale_factor_bands[band_index + 2].start, scale_factor_bands[band_index + 2].end);
sample_count += scale_factor_bands[band_index + 2].width;
band_index += 3;
}
while (sample_count < MP3::granule_size)
exponents[sample_count++] = 0;
}
return exponents;
}
ErrorOr<size_t, LoaderError> MP3LoaderPlugin::read_scale_factors(MP3::MP3Frame& frame, BigEndianInputBitStream& reservoir, size_t granule_index, size_t channel_index)
{
auto& channel = frame.channels[channel_index];
auto const& granule = channel.granules[granule_index];
size_t band_index = 0;
size_t bits_read = 0;
if (granule.window_switching_flag && granule.block_type == MP3::BlockType::Short) {
if (granule.mixed_block_flag) {
for (size_t i = 0; i < 8; i++) {
auto const bits = MP3::Tables::ScalefacCompressSlen1[granule.scalefac_compress];
channel.scale_factors[band_index++] = TRY(reservoir.read_bits(bits));
bits_read += bits;
}
for (size_t i = 3; i < 12; i++) {
auto const bits = i <= 5 ? MP3::Tables::ScalefacCompressSlen1[granule.scalefac_compress] : MP3::Tables::ScalefacCompressSlen2[granule.scalefac_compress];
channel.scale_factors[band_index++] = TRY(reservoir.read_bits(bits));
channel.scale_factors[band_index++] = TRY(reservoir.read_bits(bits));
channel.scale_factors[band_index++] = TRY(reservoir.read_bits(bits));
bits_read += 3 * bits;
}
} else {
for (size_t i = 0; i < 12; i++) {
auto const bits = i <= 5 ? MP3::Tables::ScalefacCompressSlen1[granule.scalefac_compress] : MP3::Tables::ScalefacCompressSlen2[granule.scalefac_compress];
channel.scale_factors[band_index++] = TRY(reservoir.read_bits(bits));
channel.scale_factors[band_index++] = TRY(reservoir.read_bits(bits));
channel.scale_factors[band_index++] = TRY(reservoir.read_bits(bits));
bits_read += 3 * bits;
}
}
channel.scale_factors[band_index++] = 0;
channel.scale_factors[band_index++] = 0;
channel.scale_factors[band_index++] = 0;
} else {
if ((channel.scale_factor_selection_info[0] == 0) || (granule_index == 0)) {
for (band_index = 0; band_index < 6; band_index++) {
auto const bits = MP3::Tables::ScalefacCompressSlen1[granule.scalefac_compress];
channel.scale_factors[band_index] = TRY(reservoir.read_bits(bits));
bits_read += bits;
}
}
if ((channel.scale_factor_selection_info[1] == 0) || (granule_index == 0)) {
for (band_index = 6; band_index < 11; band_index++) {
auto const bits = MP3::Tables::ScalefacCompressSlen1[granule.scalefac_compress];
channel.scale_factors[band_index] = TRY(reservoir.read_bits(bits));
bits_read += bits;
}
}
if ((channel.scale_factor_selection_info[2] == 0) || (granule_index == 0)) {
for (band_index = 11; band_index < 16; band_index++) {
auto const bits = MP3::Tables::ScalefacCompressSlen2[granule.scalefac_compress];
channel.scale_factors[band_index] = TRY(reservoir.read_bits(bits));
bits_read += bits;
}
}
if ((channel.scale_factor_selection_info[3] == 0) || (granule_index == 0)) {
for (band_index = 16; band_index < 21; band_index++) {
auto const bits = MP3::Tables::ScalefacCompressSlen2[granule.scalefac_compress];
channel.scale_factors[band_index] = TRY(reservoir.read_bits(bits));
bits_read += bits;
}
}
channel.scale_factors[21] = 0;
}
return bits_read;
}
MaybeLoaderError MP3LoaderPlugin::read_huffman_data(MP3::MP3Frame& frame, BigEndianInputBitStream& reservoir, size_t granule_index, size_t channel_index, size_t granule_bits_read)
{
auto const exponents = calculate_frame_exponents(frame, granule_index, channel_index);
auto& granule = frame.channels[channel_index].granules[granule_index];
auto const scale_factor_bands = get_scalefactor_bands(granule, frame.header.samplerate);
size_t const scale_factor_band_index1 = granule.region0_count + 1;
size_t const scale_factor_band_index2 = min(scale_factor_bands.size() - 1, scale_factor_band_index1 + granule.region1_count + 1);
bool const is_short_granule = granule.window_switching_flag && granule.block_type == MP3::BlockType::Short;
size_t const region1_start = is_short_granule ? 36 : scale_factor_bands[scale_factor_band_index1].start;
size_t const region2_start = is_short_granule ? MP3::granule_size : scale_factor_bands[scale_factor_band_index2].start;
auto requantize = [](int const sample, float const exponent) -> float {
int const sign = sample < 0 ? -1 : 1;
int const magnitude = AK::abs(sample);
return sign * AK::pow<float>(static_cast<float>(magnitude), 4 / 3.0) * exponent;
};
size_t count = 0;
// 2.4.3.4.6: "Decoding is done until all Huffman code bits have been decoded
// or until quantized values representing 576 frequency lines have been decoded,
// whichever comes first."
auto max_count = min(granule.big_values * 2, MP3::granule_size);
for (; count < max_count; count += 2) {
MP3::Tables::Huffman::HuffmanTreeXY const* tree = nullptr;
if (count < region1_start) {
tree = &MP3::Tables::Huffman::HuffmanTreesXY[granule.table_select[0]];
} else if (count < region2_start) {
tree = &MP3::Tables::Huffman::HuffmanTreesXY[granule.table_select[1]];
} else {
tree = &MP3::Tables::Huffman::HuffmanTreesXY[granule.table_select[2]];
}
if (!tree || tree->nodes.is_empty()) {
return LoaderError { LoaderError::Category::Format, m_loaded_samples, "Frame references invalid huffman table."_fly_string };
}
// Assumption: There's enough bits to read. 32 is just a placeholder for "unlimited".
// There are no 32 bit long huffman codes in the tables.
auto const entry = MP3::Tables::Huffman::huffman_decode(reservoir, tree->nodes, 32);
granule_bits_read += entry.bits_read;
if (!entry.code.has_value())
return LoaderError { LoaderError::Category::Format, m_loaded_samples, "Frame contains invalid huffman data."_fly_string };
int x = entry.code->symbol.x;
int y = entry.code->symbol.y;
if (x == 15 && tree->linbits > 0) {
x += TRY(reservoir.read_bits(tree->linbits));
granule_bits_read += tree->linbits;
}
if (x != 0) {
if (TRY(reservoir.read_bit()))
x = -x;
granule_bits_read++;
}
if (y == 15 && tree->linbits > 0) {
y += TRY(reservoir.read_bits(tree->linbits));
granule_bits_read += tree->linbits;
}
if (y != 0) {
if (TRY(reservoir.read_bit()))
y = -y;
granule_bits_read++;
}
granule.samples[count + 0] = requantize(x, exponents[count + 0]);
granule.samples[count + 1] = requantize(y, exponents[count + 1]);
}
ReadonlySpan<MP3::Tables::Huffman::HuffmanNode<MP3::Tables::Huffman::HuffmanVWXY>> count1table = granule.count1table_select ? MP3::Tables::Huffman::TreeB : MP3::Tables::Huffman::TreeA;
// count1 is not known. We have to read huffman encoded values
// until we've exhausted the granule's bits. We know the size of
// the granule from part2_3_length, which is the number of bits
// used for scalefactors and huffman data (in the granule).
while (granule_bits_read < granule.part_2_3_length && count <= MP3::granule_size - 4) {
auto const entry = MP3::Tables::Huffman::huffman_decode(reservoir, count1table, granule.part_2_3_length - granule_bits_read);
granule_bits_read += entry.bits_read;
if (!entry.code.has_value())
return LoaderError { LoaderError::Category::Format, m_loaded_samples, "Frame contains invalid huffman data."_fly_string };
int v = entry.code->symbol.v;
if (v != 0) {
if (granule_bits_read >= granule.part_2_3_length)
break;
if (TRY(reservoir.read_bit()))
v = -v;
granule_bits_read++;
}
int w = entry.code->symbol.w;
if (w != 0) {
if (granule_bits_read >= granule.part_2_3_length)
break;
if (TRY(reservoir.read_bit()))
w = -w;
granule_bits_read++;
}
int x = entry.code->symbol.x;
if (x != 0) {
if (granule_bits_read >= granule.part_2_3_length)
break;
if (TRY(reservoir.read_bit()))
x = -x;
granule_bits_read++;
}
int y = entry.code->symbol.y;
if (y != 0) {
if (granule_bits_read >= granule.part_2_3_length)
break;
if (TRY(reservoir.read_bit()))
y = -y;
granule_bits_read++;
}
granule.samples[count + 0] = requantize(v, exponents[count + 0]);
granule.samples[count + 1] = requantize(w, exponents[count + 1]);
granule.samples[count + 2] = requantize(x, exponents[count + 2]);
granule.samples[count + 3] = requantize(y, exponents[count + 3]);
count += 4;
}
if (granule_bits_read > granule.part_2_3_length) {
return LoaderError { LoaderError::Category::Format, m_loaded_samples, "Read too many bits from bit reservoir."_fly_string };
}
// 2.4.3.4.6: "If there are more Huffman code bits than necessary to decode 576 values
// they are regarded as stuffing bits and discarded."
for (size_t i = granule_bits_read; i < granule.part_2_3_length; i++) {
TRY(reservoir.read_bit());
}
return {};
}
void MP3LoaderPlugin::reorder_samples(MP3::Granule& granule, u32 sample_rate)
{
float tmp[MP3::granule_size] = {};
size_t band_index = 0;
size_t subband_index = 0;
auto scale_factor_bands = get_scalefactor_bands(granule, sample_rate);
if (granule.mixed_block_flag) {
while (subband_index < 36) {
for (size_t frequency_line_index = 0; frequency_line_index < scale_factor_bands[band_index].width; frequency_line_index++) {
tmp[subband_index] = granule.samples[subband_index];
subband_index++;
}
band_index++;
}
}
while (subband_index < MP3::granule_size && band_index <= 36) {
for (size_t frequency_line_index = 0; frequency_line_index < scale_factor_bands[band_index].width; frequency_line_index++) {
tmp[subband_index++] = granule.samples[scale_factor_bands[band_index + 0].start + frequency_line_index];
tmp[subband_index++] = granule.samples[scale_factor_bands[band_index + 1].start + frequency_line_index];
tmp[subband_index++] = granule.samples[scale_factor_bands[band_index + 2].start + frequency_line_index];
}
band_index += 3;
}
for (size_t i = 0; i < MP3::granule_size; i++)
granule.samples[i] = tmp[i];
}
void MP3LoaderPlugin::reduce_alias(MP3::Granule& granule, size_t max_subband_index)
{
for (size_t subband = 0; subband < max_subband_index - 18; subband += 18) {
for (size_t i = 0; i < 8; i++) {
size_t const idx1 = subband + 17 - i;
size_t const idx2 = subband + 18 + i;
auto const d1 = granule.samples[idx1];
auto const d2 = granule.samples[idx2];
granule.samples[idx1] = d1 * MP3::Tables::AliasReductionCs[i] - d2 * MP3::Tables::AliasReductionCa[i];
granule.samples[idx2] = d2 * MP3::Tables::AliasReductionCs[i] + d1 * MP3::Tables::AliasReductionCa[i];
}
}
}
void MP3LoaderPlugin::process_stereo(MP3::MP3Frame& frame, size_t granule_index)
{
size_t band_index_ms_start = 0;
size_t band_index_ms_end = 0;
size_t band_index_intensity_start = 0;
size_t band_index_intensity_end = 0;
auto& granule_left = frame.channels[0].granules[granule_index];
auto& granule_right = frame.channels[1].granules[granule_index];
auto get_last_nonempty_band = [](Span<float> samples, ReadonlySpan<MP3::Tables::ScaleFactorBand> bands) -> size_t {
size_t last_nonempty_band = 0;
for (size_t i = 0; i < bands.size(); i++) {
bool is_empty = true;
for (size_t l = bands[i].start; l < bands[i].end; l++) {
if (samples[l] != 0) {
is_empty = false;
break;
}
}
if (!is_empty)
last_nonempty_band = i;
}
return last_nonempty_band;
};
auto process_ms_stereo = [&](MP3::Tables::ScaleFactorBand const& band) {
float const SQRT_2 = AK::sqrt(2.0);
for (size_t i = band.start; i <= band.end; i++) {
float const m = granule_left.samples[i];
float const s = granule_right.samples[i];
granule_left.samples[i] = (m + s) / SQRT_2;
granule_right.samples[i] = (m - s) / SQRT_2;
}
};
auto process_intensity_stereo = [&](MP3::Tables::ScaleFactorBand const& band, float intensity_stereo_ratio) {
for (size_t i = band.start; i <= band.end; i++) {
// Superflous empty scale factor band.
if (i >= MP3::granule_size)
continue;
float const sample_left = granule_left.samples[i];
float const coeff_l = intensity_stereo_ratio / (1 + intensity_stereo_ratio);
float const coeff_r = 1 / (1 + intensity_stereo_ratio);
granule_left.samples[i] = sample_left * coeff_l;
granule_right.samples[i] = sample_left * coeff_r;
}
};
auto scale_factor_bands = get_scalefactor_bands(granule_right, frame.header.samplerate);
if (has_flag(frame.header.mode_extension, MP3::ModeExtension::MsStereo)) {
band_index_ms_start = 0;
band_index_ms_end = scale_factor_bands.size();
}
if (has_flag(frame.header.mode_extension, MP3::ModeExtension::IntensityStereo)) {
band_index_intensity_start = get_last_nonempty_band(granule_right.samples, scale_factor_bands);
band_index_intensity_end = scale_factor_bands.size();
band_index_ms_end = band_index_intensity_start;
}
for (size_t band_index = band_index_ms_start; band_index < band_index_ms_end; band_index++) {
process_ms_stereo(scale_factor_bands[band_index]);
}
for (size_t band_index = band_index_intensity_start; band_index < band_index_intensity_end; band_index++) {
auto const intensity_stereo_position = frame.channels[1].scale_factors[band_index];
if (intensity_stereo_position == 7) {
if (has_flag(frame.header.mode_extension, MP3::ModeExtension::MsStereo))
process_ms_stereo(scale_factor_bands[band_index]);
continue;
}
float const intensity_stereo_ratio = AK::tan(intensity_stereo_position * AK::Pi<float> / 12);
process_intensity_stereo(scale_factor_bands[band_index], intensity_stereo_ratio);
}
}
void MP3LoaderPlugin::transform_samples_to_time(Array<float, MP3::granule_size> const& input, size_t input_offset, Array<float, 36>& output, MP3::BlockType block_type)
{
if (block_type == MP3::BlockType::Short) {
size_t const N = 12;
Array<float, N * 3> temp_out;
Array<float, N / 2> temp_in;
for (size_t k = 0; k < N / 2; k++)
temp_in[k] = input[input_offset + 3 * k + 0];
s_mdct_12.transform(temp_in, Span<float>(temp_out).slice(0, N));
for (size_t i = 0; i < N; i++)
temp_out[i + 0] *= MP3::Tables::WindowBlockTypeShort[i];
for (size_t k = 0; k < N / 2; k++)
temp_in[k] = input[input_offset + 3 * k + 1];
s_mdct_12.transform(temp_in, Span<float>(temp_out).slice(12, N));
for (size_t i = 0; i < N; i++)
temp_out[i + 12] *= MP3::Tables::WindowBlockTypeShort[i];
for (size_t k = 0; k < N / 2; k++)
temp_in[k] = input[input_offset + 3 * k + 2];
s_mdct_12.transform(temp_in, Span<float>(temp_out).slice(24, N));
for (size_t i = 0; i < N; i++)
temp_out[i + 24] *= MP3::Tables::WindowBlockTypeShort[i];
Span<float> idmct1 = Span<float>(temp_out).slice(0, 12);
Span<float> idmct2 = Span<float>(temp_out).slice(12, 12);
Span<float> idmct3 = Span<float>(temp_out).slice(24, 12);
for (size_t i = 0; i < 6; i++)
output[i] = 0;
for (size_t i = 6; i < 12; i++)
output[i] = idmct1[i - 6];
for (size_t i = 12; i < 18; i++)
output[i] = idmct1[i - 6] + idmct2[i - 12];
for (size_t i = 18; i < 24; i++)
output[i] = idmct2[i - 12] + idmct3[i - 18];
for (size_t i = 24; i < 30; i++)
output[i] = idmct3[i - 18];
for (size_t i = 30; i < 36; i++)
output[i] = 0;
} else {
s_mdct_36.transform(ReadonlySpan<float>(input).slice(input_offset, 18), output);
for (size_t i = 0; i < 36; i++) {
switch (block_type) {
case MP3::BlockType::Normal:
output[i] *= MP3::Tables::WindowBlockTypeNormal[i];
break;
case MP3::BlockType::Start:
output[i] *= MP3::Tables::WindowBlockTypeStart[i];
break;
case MP3::BlockType::End:
output[i] *= MP3::Tables::WindowBlockTypeEnd[i];
break;
case MP3::BlockType::Short:
VERIFY_NOT_REACHED();
break;
}
}
}
}
// ISO/IEC 11172-3 (Figure A.2)
void MP3LoaderPlugin::synthesis(Array<float, 1024>& V, Array<float, 32>& samples, Array<float, 32>& result)
{
for (size_t i = 1023; i >= 64; i--) {
V[i] = V[i - 64];
}
for (size_t i = 0; i < 64; i++) {
V[i] = 0;
for (size_t k = 0; k < 32; k++) {
float const N = MP3::Tables::SynthesisSubbandFilterCoefficients[i][k];
V[i] += N * samples[k];
}
}
Array<float, 512> U;
for (size_t i = 0; i < 8; i++) {
for (size_t j = 0; j < 32; j++) {
U[i * 64 + j] = V[i * 128 + j];
U[i * 64 + 32 + j] = V[i * 128 + 96 + j];
}
}
Array<float, 512> W;
for (size_t i = 0; i < 512; i++) {
W[i] = U[i] * MP3::Tables::WindowSynthesis[i];
}
for (size_t j = 0; j < 32; j++) {
result[j] = 0;
for (size_t k = 0; k < 16; k++) {
result[j] += W[j + 32 * k];
}
}
}
ReadonlySpan<MP3::Tables::ScaleFactorBand> MP3LoaderPlugin::get_scalefactor_bands(MP3::Granule const& granule, int samplerate)
{
switch (granule.block_type) {
case MP3::BlockType::Short:
switch (samplerate) {
case 32000:
return granule.mixed_block_flag ? MP3::Tables::ScaleFactorBandMixed32000 : MP3::Tables::ScaleFactorBandShort32000;
case 44100:
return granule.mixed_block_flag ? MP3::Tables::ScaleFactorBandMixed44100 : MP3::Tables::ScaleFactorBandShort44100;
case 48000:
return granule.mixed_block_flag ? MP3::Tables::ScaleFactorBandMixed48000 : MP3::Tables::ScaleFactorBandShort48000;
}
break;
case MP3::BlockType::Normal:
[[fallthrough]];
case MP3::BlockType::Start:
[[fallthrough]];
case MP3::BlockType::End:
switch (samplerate) {
case 32000:
return MP3::Tables::ScaleFactorBandLong32000;
case 44100:
return MP3::Tables::ScaleFactorBandLong44100;
case 48000:
return MP3::Tables::ScaleFactorBandLong48000;
}
}
VERIFY_NOT_REACHED();
}
}
