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ladybird/Userland/Libraries/LibAudio/MP3Loader.cpp
Zaggy1024 e087d35cd8 LibAudio: Accurately skip MP3 frames using the actual header size 
Prevously, the header size was used to calculate the `slot_count` field
of `MP3::Header`, but `build_seek_table()` just used the maximum size
of the header instead, causing it not to seek far enough, and in cases
where a possible sync code occurred two bytes before the next frame, it
would read that possible sync code as if it was a real frame. It would
then either reject it due to bad field values, or could possibly skip
over the next real frame due to a larger calculated frame size in the
bogus frame.

By fixing this issue, we now properly calculate the duration of MP3
files where these fake sync codes occur. In the case of the raw file
for this podcast:

https://changelog.com/podcast/554

the duration goes from 1:21:57 to 1:22:47, which is the real duration
according to the player user interface.
2023-08-26 18:43:23 -04:00

924 lines
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/*
* 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;
auto maybe_bit_stream = try_make<BigEndianInputBitStream>(MaybeOwned<Stream>(stream));
if (maybe_bit_stream.is_error())
return false;
auto bit_stream = maybe_bit_stream.release_value();
auto synchronization_result = synchronize(*bit_stream, 0);
if (synchronization_result.is_error())
return false;
auto maybe_mp3 = stream.read_value<BigEndian<u16>>();
if (maybe_mp3.is_error())
return false;
ErrorOr<int> id = bit_stream->read_bit();
if (id.is_error() || id.value() != 1)
return false;
auto raw_layer = bit_stream->read_bits(2);
if (raw_layer.is_error())
return false;
auto layer = MP3::Tables::LayerNumberLookup[raw_layer.value()];
return layer == 3;
}
ErrorOr<NonnullOwnPtr<LoaderPlugin>, LoaderError> MP3LoaderPlugin::create(NonnullOwnPtr<SeekableStream> stream)
{
auto loader = make<MP3LoaderPlugin>(move(stream));
TRY(loader->initialize());
return loader;
}
MaybeLoaderError MP3LoaderPlugin::initialize()
{
m_bitstream = TRY(try_make<BigEndianInputBitStream>(MaybeOwned<Stream>(*m_stream)));
TRY(build_seek_table());
TRY(seek(0));
TRY(synchronize());
auto header = TRY(read_header());
if (header.id != 1 || header.layer != 3)
return LoaderError { LoaderError::Category::Format, "Only MPEG-1 layer 3 supported." };
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_current_frame = {};
m_synthesis_buffer = {};
m_loaded_samples = 0;
TRY(m_bit_reservoir.discard(m_bit_reservoir.used_buffer_size()));
m_bitstream->align_to_byte_boundary();
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_current_frame = {};
m_synthesis_buffer = {};
TRY(m_bit_reservoir.discard(m_bit_reservoir.used_buffer_size()));
m_bitstream->align_to_byte_boundary();
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));
if (!m_current_frame.has_value()) {
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();
}
m_current_frame = maybe_frame.release_value();
if (!m_current_frame.has_value())
break;
}
bool const is_stereo = m_current_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 = m_current_frame->channels[0].granules[0].pcm[current_frame_read / 32][current_frame_read % 32];
auto const right_sample = is_stereo ? m_current_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 = m_current_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 ? m_current_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)));
m_current_frame = {};
}
return frames;
}
MaybeLoaderError MP3LoaderPlugin::build_seek_table()
{
VERIFY(MUST(m_stream->tell()) == 0);
TRY(skip_id3(*m_stream));
m_bitstream->align_to_byte_boundary();
int sample_count = 0;
size_t frame_count = 0;
m_seek_table = {};
while (!synchronize().is_error()) {
auto const frame_pos = -2 + TRY(m_stream->seek(0, SeekMode::FromCurrentPosition));
auto error_or_header = read_header();
if (error_or_header.is_error() || error_or_header.value().id != 1 || error_or_header.value().layer != 3) {
continue;
}
if (frame_count % 10 == 0)
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));
// TODO: This is just here to clear the bitstream buffer.
// Bitstream should have a method to sync its state to the underlying stream.
m_bitstream->align_to_byte_boundary();
}
m_total_samples = sample_count;
return {};
}
ErrorOr<MP3::Header, LoaderError> MP3LoaderPlugin::read_header()
{
MP3::Header header;
header.id = TRY(m_bitstream->read_bit());
header.layer = MP3::Tables::LayerNumberLookup[TRY(m_bitstream->read_bits(2))];
if (header.layer <= 0)
return LoaderError { LoaderError::Category::Format, m_loaded_samples, "Frame header contains invalid layer number." };
header.protection_bit = TRY(m_bitstream->read_bit());
header.bitrate = MP3::Tables::BitratesPerLayerLookup[header.layer - 1][TRY(m_bitstream->read_bits(4))];
if (header.bitrate <= 0)
return LoaderError { LoaderError::Category::Format, m_loaded_samples, "Frame header contains invalid bitrate." };
header.samplerate = MP3::Tables::SampleratesLookup[TRY(m_bitstream->read_bits(2))];
if (header.samplerate <= 0)
return LoaderError { LoaderError::Category::Format, m_loaded_samples, "Frame header contains invalid samplerate." };
header.padding_bit = TRY(m_bitstream->read_bit());
header.private_bit = TRY(m_bitstream->read_bit());
header.mode = static_cast<MP3::Mode>(TRY(m_bitstream->read_bits(2)));
header.mode_extension = static_cast<MP3::ModeExtension>(TRY(m_bitstream->read_bits(2)));
header.copyright_bit = TRY(m_bitstream->read_bit());
header.original_bit = TRY(m_bitstream->read_bit());
header.emphasis = static_cast<MP3::Emphasis>(TRY(m_bitstream->read_bits(2)));
header.header_size = 4;
if (!header.protection_bit) {
header.crc16 = TRY(m_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;
}
MaybeLoaderError MP3LoaderPlugin::synchronize(BigEndianInputBitStream& stream, size_t sample_index)
{
size_t one_counter = 0;
while (one_counter < 12 && !stream.is_eof()) {
bool const bit = TRY(stream.read_bit());
one_counter = bit ? one_counter + 1 : 0;
if (!bit) {
stream.align_to_byte_boundary();
}
}
if (one_counter != 12)
return LoaderError { LoaderError::Category::Format, sample_index, "Failed to synchronize." };
return {};
}
MaybeLoaderError MP3LoaderPlugin::synchronize()
{
return MP3LoaderPlugin::synchronize(*m_bitstream, m_loaded_samples);
}
ErrorOr<MP3::MP3Frame, LoaderError> MP3LoaderPlugin::read_next_frame()
{
// Note: This will spin until we find a correct frame, or we reach eof.
// In the second case, the error will bubble up from read_frame_data().
while (true) {
TRY(synchronize());
MP3::Header header = TRY(read_header());
if (header.id != 1 || header.layer != 3) {
continue;
}
return read_frame_data(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" };
auto& buffer = maybe_buffer.value();
size_t old_reservoir_size = m_bit_reservoir.used_buffer_size();
TRY(m_bitstream->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)
{
frame.main_data_begin = TRY(m_bitstream->read_bits(9));
if (frame.header.channel_count() == 1) {
frame.private_bits = TRY(m_bitstream->read_bits(5));
} else {
frame.private_bits = TRY(m_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(m_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(m_bitstream->read_bits(12));
granule.big_values = TRY(m_bitstream->read_bits(9));
granule.global_gain = TRY(m_bitstream->read_bits(8));
granule.scalefac_compress = TRY(m_bitstream->read_bits(4));
granule.window_switching_flag = TRY(m_bitstream->read_bit());
if (granule.window_switching_flag) {
granule.block_type = static_cast<MP3::BlockType>(TRY(m_bitstream->read_bits(2)));
granule.mixed_block_flag = TRY(m_bitstream->read_bit());
for (size_t region = 0; region < 2; region++)
granule.table_select[region] = TRY(m_bitstream->read_bits(5));
for (size_t window = 0; window < 3; window++)
granule.sub_block_gain[window] = TRY(m_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(m_bitstream->read_bits(5));
granule.region0_count = TRY(m_bitstream->read_bits(4));
granule.region1_count = TRY(m_bitstream->read_bits(3));
}
granule.preflag = TRY(m_bitstream->read_bit());
granule.scalefac_scale = TRY(m_bitstream->read_bit());
granule.count1table_select = TRY(m_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." };
}
// 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." };
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." };
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." };
}
// 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++) {
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();
}
}
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