/*
* Copyright (c) 2021, kleines Filmröllchen <filmroellchen@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/ByteString.h>
#include <AK/Debug.h>
#include <AK/DeprecatedFlyString.h>
#include <AK/FixedArray.h>
#include <AK/Format.h>
#include <AK/Forward.h>
#include <AK/IntegralMath.h>
#include <AK/Math.h>
#include <AK/MemoryStream.h>
#include <AK/NonnullOwnPtr.h>
#include <AK/ScopeGuard.h>
#include <AK/StdLibExtras.h>
#include <AK/Try.h>
#include <AK/TypedTransfer.h>
#include <AK/UFixedBigInt.h>
#include <LibAudio/FlacLoader.h>
#include <LibAudio/FlacTypes.h>
#include <LibAudio/GenericTypes.h>
#include <LibAudio/LoaderError.h>
#include <LibAudio/MultiChannel.h>
#include <LibAudio/Resampler.h>
#include <LibAudio/VorbisComment.h>
#include <LibCore/File.h>
#include <LibCrypto/Checksum/ChecksumFunction.h>
#include <LibCrypto/Checksum/ChecksummingStream.h>
namespace Audio {
FlacLoaderPlugin::FlacLoaderPlugin(NonnullOwnPtr<SeekableStream> stream)
: LoaderPlugin(move(stream))
{
}
ErrorOr<NonnullOwnPtr<LoaderPlugin>, LoaderError> FlacLoaderPlugin::create(NonnullOwnPtr<SeekableStream> stream)
{
auto loader = make<FlacLoaderPlugin>(move(stream));
TRY(loader->initialize());
return loader;
}
MaybeLoaderError FlacLoaderPlugin::initialize()
{
TRY(parse_header());
TRY(reset());
return {};
}
bool FlacLoaderPlugin::sniff(SeekableStream& stream)
{
BigEndianInputBitStream bit_input { MaybeOwned<Stream>(stream) };
auto maybe_flac = bit_input.read_bits<u32>(32);
return !maybe_flac.is_error() && maybe_flac.value() == 0x664C6143; // "flaC"
}
// 11.5 STREAM
MaybeLoaderError FlacLoaderPlugin::parse_header()
{
BigEndianInputBitStream bit_input { MaybeOwned<Stream>(*m_stream) };
// A mixture of VERIFY and the non-crashing TRY().
#define FLAC_VERIFY(check, category, msg) \
do { \
if (!(check)) { \
return LoaderError { category, TRY(m_stream->tell()), TRY(String::formatted("FLAC header: {}", msg)) }; \
} \
} while (0)
// Magic number
u32 flac = TRY(bit_input.read_bits<u32>(32));
m_data_start_location += 4;
FLAC_VERIFY(flac == 0x664C6143, LoaderError::Category::Format, "Magic number must be 'flaC'"); // "flaC"
// Receive the streaminfo block
auto streaminfo = TRY(next_meta_block(bit_input));
FLAC_VERIFY(streaminfo.type == FlacMetadataBlockType::STREAMINFO, LoaderError::Category::Format, "First block must be STREAMINFO");
FixedMemoryStream streaminfo_data_memory { streaminfo.data.bytes() };
BigEndianInputBitStream streaminfo_data { MaybeOwned<Stream>(streaminfo_data_memory) };
// 11.10 METADATA_BLOCK_STREAMINFO
m_min_block_size = TRY(streaminfo_data.read_bits<u16>(16));
FLAC_VERIFY(m_min_block_size >= 16, LoaderError::Category::Format, "Minimum block size must be 16");
m_max_block_size = TRY(streaminfo_data.read_bits<u16>(16));
FLAC_VERIFY(m_max_block_size >= 16, LoaderError::Category::Format, "Maximum block size");
m_min_frame_size = TRY(streaminfo_data.read_bits<u32>(24));
m_max_frame_size = TRY(streaminfo_data.read_bits<u32>(24));
m_sample_rate = TRY(streaminfo_data.read_bits<u32>(20));
FLAC_VERIFY(m_sample_rate <= 655350, LoaderError::Category::Format, "Sample rate");
m_num_channels = TRY(streaminfo_data.read_bits<u8>(3)) + 1; // 0 = one channel
m_bits_per_sample = TRY(streaminfo_data.read_bits<u8>(5)) + 1;
if (m_bits_per_sample <= 8) {
// FIXME: Signed/Unsigned issues?
m_sample_format = PcmSampleFormat::Uint8;
} else if (m_bits_per_sample <= 16) {
m_sample_format = PcmSampleFormat::Int16;
} else if (m_bits_per_sample <= 24) {
m_sample_format = PcmSampleFormat::Int24;
} else if (m_bits_per_sample <= 32) {
m_sample_format = PcmSampleFormat::Int32;
} else {
FLAC_VERIFY(false, LoaderError::Category::Format, "Sample bit depth too large");
}
m_total_samples = TRY(streaminfo_data.read_bits<u64>(36));
if (m_total_samples == 0) {
// "A value of zero here means the number of total samples is unknown."
dbgln("FLAC Warning: File has unknown amount of samples, the loader will not stop before EOF");
m_total_samples = NumericLimits<decltype(m_total_samples)>::max();
}
VERIFY(streaminfo_data.is_aligned_to_byte_boundary());
TRY(streaminfo_data.read_until_filled({ m_md5_checksum, sizeof(m_md5_checksum) }));
// Parse other blocks
[[maybe_unused]] u16 meta_blocks_parsed = 1;
[[maybe_unused]] u16 total_meta_blocks = meta_blocks_parsed;
FlacRawMetadataBlock block = streaminfo;
while (!block.is_last_block) {
block = TRY(next_meta_block(bit_input));
switch (block.type) {
case (FlacMetadataBlockType::SEEKTABLE):
TRY(load_seektable(block));
break;
case FlacMetadataBlockType::PICTURE:
TRY(load_picture(block));
break;
case FlacMetadataBlockType::APPLICATION:
// Note: Third-party library can encode specific data in this.
dbgln("FLAC Warning: Unknown 'Application' metadata block encountered.");
[[fallthrough]];
case FlacMetadataBlockType::PADDING:
// Note: A padding block is empty and does not need any treatment.
break;
case FlacMetadataBlockType::VORBIS_COMMENT:
load_vorbis_comment(block);
break;
default:
// TODO: Parse the remaining metadata block types.
break;
}
++total_meta_blocks;
}
dbgln_if(AFLACLOADER_DEBUG, "Parsed FLAC header: blocksize {}-{}{}, framesize {}-{}, {}Hz, {}bit, {} channels, {} samples total ({:.2f}s), MD5 {:hex-dump}, data start at {:x} bytes, {} headers total (skipped {})", m_min_block_size, m_max_block_size, is_fixed_blocksize_stream() ? " (constant)" : "", m_min_frame_size, m_max_frame_size, m_sample_rate, pcm_bits_per_sample(m_sample_format), m_num_channels, m_total_samples, static_cast<float>(m_total_samples) / static_cast<float>(m_sample_rate), ReadonlyBytes { m_md5_checksum }, m_data_start_location, total_meta_blocks, total_meta_blocks - meta_blocks_parsed);
TRY(m_seektable.insert_seek_point({ 0, 0 }));
return {};
}
// 11.19. METADATA_BLOCK_PICTURE
MaybeLoaderError FlacLoaderPlugin::load_picture(FlacRawMetadataBlock& block)
{
FixedMemoryStream memory_stream { block.data.bytes() };
BigEndianInputBitStream picture_block_bytes { MaybeOwned<Stream>(memory_stream) };
PictureData picture;
picture.type = static_cast<ID3PictureType>(TRY(picture_block_bytes.read_bits(32)));
auto const mime_string_length = TRY(picture_block_bytes.read_bits(32));
auto offset_before_seeking = memory_stream.offset();
if (offset_before_seeking + mime_string_length >= block.data.size())
return LoaderError { LoaderError::Category::Format, TRY(m_stream->tell()), "Picture MIME type exceeds available data"_fly_string };
// "The MIME type string, in printable ASCII characters 0x20-0x7E."
picture.mime_string = TRY(String::from_stream(memory_stream, mime_string_length));
for (auto code_point : picture.mime_string.code_points()) {
if (code_point < 0x20 || code_point > 0x7E)
return LoaderError { LoaderError::Category::Format, TRY(m_stream->tell()), "Picture MIME type is not ASCII in range 0x20 - 0x7E"_fly_string };
}
auto const description_string_length = TRY(picture_block_bytes.read_bits(32));
offset_before_seeking = memory_stream.offset();
if (offset_before_seeking + description_string_length >= block.data.size())
return LoaderError { LoaderError::Category::Format, TRY(m_stream->tell()), "Picture description exceeds available data"_fly_string };
picture.description_string = TRY(String::from_stream(memory_stream, description_string_length));
picture.width = TRY(picture_block_bytes.read_bits(32));
picture.height = TRY(picture_block_bytes.read_bits(32));
picture.color_depth = TRY(picture_block_bytes.read_bits(32));
picture.colors = TRY(picture_block_bytes.read_bits(32));
auto const picture_size = TRY(picture_block_bytes.read_bits(32));
offset_before_seeking = memory_stream.offset();
if (offset_before_seeking + picture_size > block.data.size())
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(TRY(m_stream->tell())), "Picture size exceeds available data"_fly_string };
TRY(memory_stream.seek(picture_size, SeekMode::FromCurrentPosition));
picture.data = Vector<u8> { block.data.bytes().slice(offset_before_seeking, picture_size) };
m_pictures.append(move(picture));
return {};
}
// 11.15. METADATA_BLOCK_VORBIS_COMMENT
void FlacLoaderPlugin::load_vorbis_comment(FlacRawMetadataBlock& block)
{
auto metadata_or_error = Audio::load_vorbis_comment(block.data);
if (metadata_or_error.is_error()) {
dbgln("FLAC Warning: Vorbis comment invalid, error: {}", metadata_or_error.release_error());
return;
}
m_metadata = metadata_or_error.release_value();
}
// 11.13. METADATA_BLOCK_SEEKTABLE
MaybeLoaderError FlacLoaderPlugin::load_seektable(FlacRawMetadataBlock& block)
{
FixedMemoryStream memory_stream { block.data.bytes() };
BigEndianInputBitStream seektable_bytes { MaybeOwned<Stream>(memory_stream) };
for (size_t i = 0; i < block.length / 18; ++i) {
// 11.14. SEEKPOINT
u64 sample_index = TRY(seektable_bytes.read_bits<u64>(64));
u64 byte_offset = TRY(seektable_bytes.read_bits<u64>(64));
// The sample count of a seek point is not relevant to us.
[[maybe_unused]] u16 sample_count = TRY(seektable_bytes.read_bits<u16>(16));
// Placeholder, to be ignored.
if (sample_index == 0xFFFFFFFFFFFFFFFF)
continue;
SeekPoint seekpoint {
.sample_index = sample_index,
.byte_offset = byte_offset,
};
TRY(m_seektable.insert_seek_point(seekpoint));
}
dbgln_if(AFLACLOADER_DEBUG, "Loaded seektable of size {}", m_seektable.size());
return {};
}
// 11.6 METADATA_BLOCK
ErrorOr<FlacRawMetadataBlock, LoaderError> FlacLoaderPlugin::next_meta_block(BigEndianInputBitStream& bit_input)
{
// 11.7 METADATA_BLOCK_HEADER
bool is_last_block = TRY(bit_input.read_bit());
// The block type enum constants agree with the specification
FlacMetadataBlockType type = (FlacMetadataBlockType)TRY(bit_input.read_bits<u8>(7));
m_data_start_location += 1;
FLAC_VERIFY(type != FlacMetadataBlockType::INVALID, LoaderError::Category::Format, "Invalid metadata block");
u32 block_length = TRY(bit_input.read_bits<u32>(24));
m_data_start_location += 3;
// Blocks can be zero-sized, which would trip up the raw data reader below.
if (block_length == 0)
return FlacRawMetadataBlock {
.is_last_block = is_last_block,
.type = type,
.length = 0,
.data = TRY(ByteBuffer::create_uninitialized(0))
};
auto block_data_result = ByteBuffer::create_uninitialized(block_length);
FLAC_VERIFY(!block_data_result.is_error(), LoaderError::Category::IO, "Out of memory");
auto block_data = block_data_result.release_value();
TRY(bit_input.read_until_filled(block_data));
m_data_start_location += block_length;
return FlacRawMetadataBlock {
is_last_block,
type,
block_length,
block_data,
};
}
#undef FLAC_VERIFY
MaybeLoaderError FlacLoaderPlugin::reset()
{
TRY(seek(0));
m_current_frame.clear();
return {};
}
MaybeLoaderError FlacLoaderPlugin::seek(int int_sample_index)
{
auto sample_index = static_cast<size_t>(int_sample_index);
if (sample_index == m_loaded_samples)
return {};
auto maybe_target_seekpoint = m_seektable.seek_point_before(sample_index);
// No seektable or no fitting entry: Perform normal forward read
if (!maybe_target_seekpoint.has_value()) {
if (sample_index < m_loaded_samples) {
TRY(m_stream->seek(m_data_start_location, SeekMode::SetPosition));
m_loaded_samples = 0;
}
if (sample_index - m_loaded_samples == 0)
return {};
dbgln_if(AFLACLOADER_DEBUG, "Seeking {} samples manually", sample_index - m_loaded_samples);
} else {
auto target_seekpoint = maybe_target_seekpoint.release_value();
// When a small seek happens, we may already be closer to the target than the seekpoint.
if (sample_index - target_seekpoint.sample_index > sample_index - m_loaded_samples) {
dbgln_if(AFLACLOADER_DEBUG, "Close enough to target ({} samples): ignoring seek point", sample_index - m_loaded_samples);
} else {
dbgln_if(AFLACLOADER_DEBUG, "Seeking to seektable: sample index {}, byte offset {}", target_seekpoint.sample_index, target_seekpoint.byte_offset);
auto position = target_seekpoint.byte_offset + m_data_start_location;
if (m_stream->seek(static_cast<i64>(position), SeekMode::SetPosition).is_error())
return LoaderError { LoaderError::Category::IO, m_loaded_samples, TRY(String::formatted("Invalid seek position {}", position)) };
m_loaded_samples = target_seekpoint.sample_index;
}
}
// Skip frames until we're just before the target sample.
VERIFY(m_loaded_samples <= sample_index);
size_t frame_start_location;
while (m_loaded_samples <= sample_index) {
frame_start_location = TRY(m_stream->tell());
(void)TRY(next_frame());
m_loaded_samples += m_current_frame->sample_count;
}
TRY(m_stream->seek(frame_start_location, SeekMode::SetPosition));
return {};
}
bool FlacLoaderPlugin::should_insert_seekpoint_at(u64 sample_index) const
{
auto const max_seekpoint_distance = (maximum_seekpoint_distance_ms * m_sample_rate) / 1000;
auto const seek_tolerance = (seek_tolerance_ms * m_sample_rate) / 1000;
auto const current_seekpoint_distance = m_seektable.seek_point_sample_distance_around(sample_index).value_or(NumericLimits<u64>::max());
auto const previous_seekpoint = m_seektable.seek_point_before(sample_index);
auto const distance_to_previous_seekpoint = previous_seekpoint.has_value() ? sample_index - previous_seekpoint->sample_index : NumericLimits<u64>::max();
// We insert a seekpoint only under two conditions:
// - The seek points around us are spaced too far for what the loader recommends.
// Prevents inserting too many seek points between pre-loaded seek points.
// - We are so far away from the previous seek point that seeking will become too imprecise if we don't insert a seek point at least here.
// Prevents inserting too many seek points at the end of files without pre-loaded seek points.
return current_seekpoint_distance >= max_seekpoint_distance && distance_to_previous_seekpoint >= seek_tolerance;
}
ErrorOr<Vector<FixedArray<Sample>>, LoaderError> FlacLoaderPlugin::load_chunks(size_t samples_to_read_from_input)
{
ssize_t remaining_samples = static_cast<ssize_t>(m_total_samples - m_loaded_samples);
// The first condition is relevant for unknown-size streams (total samples = 0 in the header)
if (m_stream->is_eof() || (m_total_samples < NumericLimits<u64>::max() && remaining_samples <= 0))
return Vector<FixedArray<Sample>> {};
size_t samples_to_read = min(samples_to_read_from_input, remaining_samples);
Vector<FixedArray<Sample>> frames;
// In this case we can know exactly how many frames we're going to read.
if (is_fixed_blocksize_stream() && m_current_frame.has_value())
TRY(frames.try_ensure_capacity(samples_to_read / m_current_frame->sample_count + 1));
size_t sample_index = 0;
while (!m_stream->is_eof() && sample_index < samples_to_read) {
TRY(frames.try_append(TRY(next_frame())));
sample_index += m_current_frame->sample_count;
}
m_loaded_samples += sample_index;
return frames;
}
// 11.21. FRAME
LoaderSamples FlacLoaderPlugin::next_frame()
{
#define FLAC_VERIFY(check, category, msg) \
do { \
if (!(check)) { \
return LoaderError { category, static_cast<size_t>(m_current_sample_or_frame), TRY(String::formatted("FLAC header: {}", msg)) }; \
} \
} while (0)
auto frame_byte_index = TRY(m_stream->tell());
auto sample_index = m_loaded_samples;
// Insert a new seek point if we don't have enough here.
if (should_insert_seekpoint_at(sample_index)) {
dbgln_if(AFLACLOADER_DEBUG, "Inserting ad-hoc seek point for sample {} at byte {:x} (seekpoint spacing {} samples)", sample_index, frame_byte_index, m_seektable.seek_point_sample_distance_around(sample_index).value_or(NumericLimits<u64>::max()));
auto maybe_error = m_seektable.insert_seek_point({ .sample_index = sample_index, .byte_offset = frame_byte_index - m_data_start_location });
if (maybe_error.is_error())
dbgln("FLAC Warning: Inserting seek point for sample {} failed: {}", sample_index, maybe_error.release_error());
}
auto frame_checksum_stream = TRY(try_make<Crypto::Checksum::ChecksummingStream<IBMCRC>>(MaybeOwned<Stream>(*m_stream)));
auto header_checksum_stream = TRY(try_make<Crypto::Checksum::ChecksummingStream<FlacFrameHeaderCRC>>(MaybeOwned<Stream>(*frame_checksum_stream)));
BigEndianInputBitStream bit_stream { MaybeOwned<Stream> { *header_checksum_stream } };
// 11.22. FRAME_HEADER
u16 sync_code = TRY(bit_stream.read_bits<u16>(14));
FLAC_VERIFY(sync_code == 0b11111111111110, LoaderError::Category::Format, "Sync code");
bool reserved_bit = TRY(bit_stream.read_bit());
FLAC_VERIFY(reserved_bit == 0, LoaderError::Category::Format, "Reserved frame header bit");
// 11.22.2. BLOCKING STRATEGY
[[maybe_unused]] bool blocking_strategy = TRY(bit_stream.read_bit());
u32 sample_count = TRY(convert_sample_count_code(TRY(bit_stream.read_bits<u8>(4))));
u32 frame_sample_rate = TRY(convert_sample_rate_code(TRY(bit_stream.read_bits<u8>(4))));
u8 channel_type_num = TRY(bit_stream.read_bits<u8>(4));
FLAC_VERIFY(channel_type_num < 0b1011, LoaderError::Category::Format, "Channel assignment");
FlacFrameChannelType channel_type = (FlacFrameChannelType)channel_type_num;
u8 bit_depth = TRY(convert_bit_depth_code(TRY(bit_stream.read_bits<u8>(3))));
reserved_bit = TRY(bit_stream.read_bit());
FLAC_VERIFY(reserved_bit == 0, LoaderError::Category::Format, "Reserved frame header end bit");
// 11.22.8. CODED NUMBER
m_current_sample_or_frame = TRY(read_utf8_char(bit_stream));
// Conditional header variables
// 11.22.9. BLOCK SIZE INT
if (sample_count == FLAC_BLOCKSIZE_AT_END_OF_HEADER_8) {
sample_count = TRY(bit_stream.read_bits<u32>(8)) + 1;
} else if (sample_count == FLAC_BLOCKSIZE_AT_END_OF_HEADER_16) {
sample_count = TRY(bit_stream.read_bits<u32>(16)) + 1;
}
// 11.22.10. SAMPLE RATE INT
if (frame_sample_rate == FLAC_SAMPLERATE_AT_END_OF_HEADER_8) {
frame_sample_rate = TRY(bit_stream.read_bits<u32>(8)) * 1000;
} else if (frame_sample_rate == FLAC_SAMPLERATE_AT_END_OF_HEADER_16) {
frame_sample_rate = TRY(bit_stream.read_bits<u32>(16));
} else if (frame_sample_rate == FLAC_SAMPLERATE_AT_END_OF_HEADER_16X10) {
frame_sample_rate = TRY(bit_stream.read_bits<u32>(16)) * 10;
}
// It does not matter whether we extract the checksum from the digest here, or extract the digest 0x00 after processing the checksum.
auto const calculated_header_checksum = header_checksum_stream->digest();
// 11.22.11. FRAME CRC
u8 specified_header_checksum = TRY(bit_stream.read_bits<u8>(8));
VERIFY(bit_stream.is_aligned_to_byte_boundary());
if (specified_header_checksum != calculated_header_checksum)
dbgln("FLAC frame {}: Calculated header checksum {:02x} is different from specified checksum {:02x}", m_current_sample_or_frame, calculated_header_checksum, specified_header_checksum);
dbgln_if(AFLACLOADER_DEBUG, "Frame: {} samples, {}bit {}Hz, channeltype {:x}, {} number {}, header checksum {:02x}{}", sample_count, bit_depth, frame_sample_rate, channel_type_num, blocking_strategy ? "sample" : "frame", m_current_sample_or_frame, specified_header_checksum, specified_header_checksum != calculated_header_checksum ? " (checksum error)"sv : ""sv);
m_current_frame = FlacFrameHeader {
.sample_rate = frame_sample_rate,
.sample_count = static_cast<u16>(sample_count),
.sample_or_frame_index = static_cast<u32>(m_current_sample_or_frame),
.blocking_strategy = static_cast<BlockingStrategy>(blocking_strategy),
.channels = channel_type,
.bit_depth = bit_depth,
.checksum = specified_header_checksum,
};
u8 subframe_count = frame_channel_type_to_channel_count(channel_type);
TRY(m_subframe_buffers.try_resize_and_keep_capacity(subframe_count));
float sample_rescale = 1 / static_cast<float>(1 << (m_current_frame->bit_depth - 1));
dbgln_if(AFLACLOADER_DEBUG, "Samples will be rescaled from {} bits: factor {:.8f}", m_current_frame->bit_depth, sample_rescale);
for (u8 i = 0; i < subframe_count; ++i) {
FlacSubframeHeader new_subframe = TRY(next_subframe_header(bit_stream, i));
auto& subframe_samples = m_subframe_buffers[i];
subframe_samples.clear_with_capacity();
TRY(parse_subframe(subframe_samples, new_subframe, bit_stream));
// We only verify the sample count for the common case of a constant sample rate.
if (m_sample_rate == m_current_frame->sample_rate)
VERIFY(subframe_samples.size() == m_current_frame->sample_count);
}
// 11.2. Overview ("The audio data is composed of...")
bit_stream.align_to_byte_boundary();
// 11.23. FRAME_FOOTER
auto const calculated_frame_checksum = frame_checksum_stream->digest();
auto const specified_frame_checksum = TRY(bit_stream.read_bits<u16>(16));
if (calculated_frame_checksum != specified_frame_checksum)
dbgln("FLAC frame {}: Calculated frame checksum {:04x} is different from specified checksum {:04x}", m_current_sample_or_frame, calculated_frame_checksum, specified_frame_checksum);
dbgln_if(AFLACLOADER_DEBUG, "Subframe footer checksum: {:04x}{}", specified_frame_checksum, specified_frame_checksum != calculated_frame_checksum ? " (checksum error)"sv : ""sv);
FixedArray<Sample> samples;
switch (channel_type) {
case FlacFrameChannelType::Mono:
case FlacFrameChannelType::Stereo:
case FlacFrameChannelType::StereoCenter:
case FlacFrameChannelType::Surround4p0:
case FlacFrameChannelType::Surround5p0:
case FlacFrameChannelType::Surround5p1:
case FlacFrameChannelType::Surround6p1:
case FlacFrameChannelType::Surround7p1: {
auto new_samples = TRY(downmix_surround_to_stereo<Vector<i64>>(m_subframe_buffers, sample_rescale));
samples.swap(new_samples);
break;
}
case FlacFrameChannelType::LeftSideStereo: {
auto new_samples = TRY(FixedArray<Sample>::create(m_current_frame->sample_count));
samples.swap(new_samples);
// channels are left (0) and side (1)
for (size_t i = 0; i < m_current_frame->sample_count; ++i) {
// right = left - side
samples[i] = { static_cast<float>(m_subframe_buffers[0][i]) * sample_rescale,
static_cast<float>(m_subframe_buffers[0][i] - m_subframe_buffers[1][i]) * sample_rescale };
}
break;
}
case FlacFrameChannelType::RightSideStereo: {
auto new_samples = TRY(FixedArray<Sample>::create(m_current_frame->sample_count));
samples.swap(new_samples);
// channels are side (0) and right (1)
for (size_t i = 0; i < m_current_frame->sample_count; ++i) {
// left = right + side
samples[i] = { static_cast<float>(m_subframe_buffers[1][i] + m_subframe_buffers[0][i]) * sample_rescale,
static_cast<float>(m_subframe_buffers[1][i]) * sample_rescale };
}
break;
}
case FlacFrameChannelType::MidSideStereo: {
auto new_samples = TRY(FixedArray<Sample>::create(m_current_frame->sample_count));
samples.swap(new_samples);
// channels are mid (0) and side (1)
for (size_t i = 0; i < m_subframe_buffers[0].size(); ++i) {
i64 mid = m_subframe_buffers[0][i];
i64 side = m_subframe_buffers[1][i];
mid *= 2;
// prevent integer division errors
samples[i] = { static_cast<float>(mid + side) * .5f * sample_rescale,
static_cast<float>(mid - side) * .5f * sample_rescale };
}
break;
}
}
return samples;
#undef FLAC_VERIFY
}
// 11.22.3. INTERCHANNEL SAMPLE BLOCK SIZE
ErrorOr<u32, LoaderError> FlacLoaderPlugin::convert_sample_count_code(u8 sample_count_code)
{
// single codes
switch (sample_count_code) {
case 0:
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Reserved block size"_fly_string };
case 1:
return 192;
case 6:
return FLAC_BLOCKSIZE_AT_END_OF_HEADER_8;
case 7:
return FLAC_BLOCKSIZE_AT_END_OF_HEADER_16;
}
if (sample_count_code >= 2 && sample_count_code <= 5) {
return 576 * AK::exp2(sample_count_code - 2);
}
return 256 * AK::exp2(sample_count_code - 8);
}
// 11.22.4. SAMPLE RATE
ErrorOr<u32, LoaderError> FlacLoaderPlugin::convert_sample_rate_code(u8 sample_rate_code)
{
switch (sample_rate_code) {
case 0:
return m_sample_rate;
case 1:
return 88200;
case 2:
return 176400;
case 3:
return 192000;
case 4:
return 8000;
case 5:
return 16000;
case 6:
return 22050;
case 7:
return 24000;
case 8:
return 32000;
case 9:
return 44100;
case 10:
return 48000;
case 11:
return 96000;
case 12:
return FLAC_SAMPLERATE_AT_END_OF_HEADER_8;
case 13:
return FLAC_SAMPLERATE_AT_END_OF_HEADER_16;
case 14:
return FLAC_SAMPLERATE_AT_END_OF_HEADER_16X10;
default:
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Invalid sample rate code"_fly_string };
}
}
// 11.22.6. SAMPLE SIZE
ErrorOr<u8, LoaderError> FlacLoaderPlugin::convert_bit_depth_code(u8 bit_depth_code)
{
switch (bit_depth_code) {
case 0:
return m_bits_per_sample;
case 1:
return 8;
case 2:
return 12;
case 3:
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Reserved sample size"_fly_string };
case 4:
return 16;
case 5:
return 20;
case 6:
return 24;
case 7:
return 32;
default:
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), TRY(String::formatted("Unsupported sample size {}", bit_depth_code)) };
}
}
// 11.22.5. CHANNEL ASSIGNMENT
u8 frame_channel_type_to_channel_count(FlacFrameChannelType channel_type)
{
if (channel_type <= FlacFrameChannelType::Surround7p1)
return to_underlying(channel_type) + 1;
return 2;
}
// 11.25. SUBFRAME_HEADER
ErrorOr<FlacSubframeHeader, LoaderError> FlacLoaderPlugin::next_subframe_header(BigEndianInputBitStream& bit_stream, u8 channel_index)
{
u8 bits_per_sample = m_current_frame->bit_depth;
// For inter-channel correlation, the side channel needs an extra bit for its samples
switch (m_current_frame->channels) {
case FlacFrameChannelType::LeftSideStereo:
case FlacFrameChannelType::MidSideStereo:
if (channel_index == 1) {
++bits_per_sample;
}
break;
case FlacFrameChannelType::RightSideStereo:
if (channel_index == 0) {
++bits_per_sample;
}
break;
// "normal" channel types
default:
break;
}
// zero-bit padding
if (TRY(bit_stream.read_bit()) != 0)
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Zero bit padding"_fly_string };
// 11.25.1. SUBFRAME TYPE
u8 subframe_code = TRY(bit_stream.read_bits<u8>(6));
if ((subframe_code >= 0b000010 && subframe_code <= 0b000111) || (subframe_code > 0b001100 && subframe_code < 0b100000))
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Subframe type"_fly_string };
FlacSubframeType subframe_type;
u8 order = 0;
// LPC has the highest bit set
if ((subframe_code & 0b100000) > 0) {
subframe_type = FlacSubframeType::LPC;
order = (subframe_code & 0b011111) + 1;
} else if ((subframe_code & 0b001000) > 0) {
// Fixed has the third-highest bit set
subframe_type = FlacSubframeType::Fixed;
order = (subframe_code & 0b000111);
} else {
subframe_type = (FlacSubframeType)subframe_code;
}
// 11.25.2. WASTED BITS PER SAMPLE FLAG
bool has_wasted_bits = TRY(bit_stream.read_bit());
u8 k = 0;
if (has_wasted_bits) {
bool current_k_bit = 0;
do {
current_k_bit = TRY(bit_stream.read_bit());
++k;
} while (current_k_bit != 1);
}
return FlacSubframeHeader {
subframe_type,
order,
k,
bits_per_sample
};
}
ErrorOr<void, LoaderError> FlacLoaderPlugin::parse_subframe(Vector<i64>& samples, FlacSubframeHeader& subframe_header, BigEndianInputBitStream& bit_input)
{
TRY(samples.try_ensure_capacity(m_current_frame->sample_count));
switch (subframe_header.type) {
case FlacSubframeType::Constant: {
// 11.26. SUBFRAME_CONSTANT
u64 constant_value = TRY(bit_input.read_bits<u64>(subframe_header.bits_per_sample - subframe_header.wasted_bits_per_sample));
dbgln_if(AFLACLOADER_DEBUG, " Constant subframe: {}", constant_value);
VERIFY(subframe_header.bits_per_sample - subframe_header.wasted_bits_per_sample != 0);
i64 constant = AK::sign_extend(static_cast<u64>(constant_value), subframe_header.bits_per_sample - subframe_header.wasted_bits_per_sample);
for (u64 i = 0; i < m_current_frame->sample_count; ++i) {
samples.unchecked_append(constant);
}
break;
}
case FlacSubframeType::Fixed: {
dbgln_if(AFLACLOADER_DEBUG, " Fixed LPC subframe order {}", subframe_header.order);
samples = TRY(decode_fixed_lpc(subframe_header, bit_input));
break;
}
case FlacSubframeType::Verbatim: {
dbgln_if(AFLACLOADER_DEBUG, " Verbatim subframe");
samples = TRY(decode_verbatim(subframe_header, bit_input));
break;
}
case FlacSubframeType::LPC: {
dbgln_if(AFLACLOADER_DEBUG, " Custom LPC subframe order {}", subframe_header.order);
TRY(decode_custom_lpc(samples, subframe_header, bit_input));
break;
}
default:
return LoaderError { LoaderError::Category::Unimplemented, static_cast<size_t>(m_current_sample_or_frame), "Unhandled FLAC subframe type"_fly_string };
}
for (size_t i = 0; i < samples.size(); ++i) {
samples[i] <<= subframe_header.wasted_bits_per_sample;
}
// Resamplers VERIFY that the sample rate is non-zero.
if (m_current_frame->sample_rate == 0 || m_sample_rate == 0
|| m_current_frame->sample_rate == m_sample_rate)
return {};
ResampleHelper<i64> resampler(m_current_frame->sample_rate, m_sample_rate);
samples = resampler.resample(samples);
return {};
}
// 11.29. SUBFRAME_VERBATIM
// Decode a subframe that isn't actually encoded, usually seen in random data
ErrorOr<Vector<i64>, LoaderError> FlacLoaderPlugin::decode_verbatim(FlacSubframeHeader& subframe, BigEndianInputBitStream& bit_input)
{
Vector<i64> decoded;
decoded.ensure_capacity(m_current_frame->sample_count);
if (subframe.bits_per_sample <= subframe.wasted_bits_per_sample) {
return LoaderError {
LoaderError::Category::Format,
TRY(m_stream->tell()),
"Effective verbatim bits per sample are zero"_fly_string,
};
}
for (size_t i = 0; i < m_current_frame->sample_count; ++i) {
decoded.unchecked_append(AK::sign_extend(
TRY(bit_input.read_bits<u64>(subframe.bits_per_sample - subframe.wasted_bits_per_sample)),
subframe.bits_per_sample - subframe.wasted_bits_per_sample));
}
return decoded;
}
// 11.28. SUBFRAME_LPC
// Decode a subframe encoded with a custom linear predictor coding, i.e. the subframe provides the polynomial order and coefficients
ErrorOr<void, LoaderError> FlacLoaderPlugin::decode_custom_lpc(Vector<i64>& decoded, FlacSubframeHeader& subframe, BigEndianInputBitStream& bit_input)
{
// LPC must provide at least as many samples as its order.
if (subframe.order > m_current_frame->sample_count)
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Too small frame for LPC order"_fly_string };
decoded.ensure_capacity(m_current_frame->sample_count);
if (subframe.bits_per_sample <= subframe.wasted_bits_per_sample) {
return LoaderError {
LoaderError::Category::Format,
TRY(m_stream->tell()),
"Effective verbatim bits per sample are zero"_fly_string,
};
}
// warm-up samples
for (auto i = 0; i < subframe.order; ++i) {
decoded.unchecked_append(AK::sign_extend(
TRY(bit_input.read_bits<u64>(subframe.bits_per_sample - subframe.wasted_bits_per_sample)),
subframe.bits_per_sample - subframe.wasted_bits_per_sample));
}
// precision of the coefficients
u8 lpc_precision = TRY(bit_input.read_bits<u8>(4));
if (lpc_precision == 0b1111)
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Invalid linear predictor coefficient precision"_fly_string };
lpc_precision += 1;
// shift needed on the data (signed!)
i8 lpc_shift = static_cast<i8>(AK::sign_extend(TRY(bit_input.read_bits<u8>(5)), 5));
Vector<i64, 32> coefficients;
coefficients.ensure_capacity(subframe.order);
// read coefficients
for (auto i = 0; i < subframe.order; ++i) {
u64 raw_coefficient = TRY(bit_input.read_bits<u64>(lpc_precision));
i64 coefficient = AK::sign_extend(raw_coefficient, lpc_precision);
coefficients.unchecked_append(coefficient);
}
dbgln_if(AFLACLOADER_DEBUG, " {}-bit {} shift coefficients: {}", lpc_precision, lpc_shift, coefficients);
TRY(decode_residual(decoded, subframe, bit_input));
// approximate the waveform with the predictor
for (size_t i = subframe.order; i < m_current_frame->sample_count; ++i) {
// (see below)
Checked<i64> sample = 0;
for (size_t t = 0; t < subframe.order; ++t) {
// It's really important that we compute in 64-bit land here.
// Even though FLAC operates at a maximum bit depth of 32 bits, modern encoders use super-large coefficients for maximum compression.
// These will easily overflow 32 bits and cause strange white noise that abruptly stops intermittently (at the end of a frame).
// The simple fix of course is to do intermediate computations in 64 bits, but we additionally use saturating arithmetic.
// These considerations are not in the original FLAC spec, but have been added to the IETF standard: https://datatracker.ietf.org/doc/html/draft-ietf-cellar-flac-03#appendix-A.3
sample.saturating_add(Checked<i64>::saturating_mul(static_cast<i64>(coefficients[t]), static_cast<i64>(decoded[i - t - 1])));
}
decoded[i] += lpc_shift >= 0 ? (sample.value() >> lpc_shift) : (sample.value() << -lpc_shift);
}
return {};
}
// 11.27. SUBFRAME_FIXED
// Decode a subframe encoded with one of the fixed linear predictor codings
ErrorOr<Vector<i64>, LoaderError> FlacLoaderPlugin::decode_fixed_lpc(FlacSubframeHeader& subframe, BigEndianInputBitStream& bit_input)
{
// LPC must provide at least as many samples as its order.
if (subframe.order > m_current_frame->sample_count)
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Too small frame for LPC order"_fly_string };
Vector<i64> decoded;
decoded.ensure_capacity(m_current_frame->sample_count);
if (subframe.bits_per_sample <= subframe.wasted_bits_per_sample) {
return LoaderError {
LoaderError::Category::Format,
TRY(m_stream->tell()),
"Effective verbatim bits per sample are zero"_fly_string,
};
}
// warm-up samples
for (auto i = 0; i < subframe.order; ++i) {
decoded.unchecked_append(AK::sign_extend(
TRY(bit_input.read_bits<u64>(subframe.bits_per_sample - subframe.wasted_bits_per_sample)),
subframe.bits_per_sample - subframe.wasted_bits_per_sample));
}
TRY(decode_residual(decoded, subframe, bit_input));
dbgln_if(AFLACLOADER_DEBUG, " decoded length {}, {} order predictor, now at file offset {:x}", decoded.size(), subframe.order, TRY(m_stream->tell()));
// Skip these comments if you don't care about the neat math behind fixed LPC :^)
// These coefficients for the recursive prediction formula are the only ones that can be resolved to polynomial predictor functions.
// The order equals the degree of the polynomial - 1, so the second-order predictor has an underlying polynomial of degree 1, a straight line.
// More specifically, the closest approximation to a polynomial is used, and the degree depends on how many previous values are available.
// This makes use of a very neat property of polynomials, which is that they are entirely characterized by their finitely many derivatives.
// (Mathematically speaking, the infinite Taylor series of any polynomial equals the polynomial itself.)
// Now remember that derivation is just the slope of the function, which is the same as the difference of two close-by values.
// Therefore, with two samples we can calculate the first derivative at a sample via the difference, which gives us a polynomial of degree 1.
// With three samples, we can do the same but also calculate the second derivative via the difference in the first derivatives.
// This gives us a polynomial of degree 2, as it has two "proper" (non-constant) derivatives.
// This can be continued for higher-order derivatives when we have more coefficients, giving us higher-order polynomials.
// In essence, it's akin to a Lagrangian polynomial interpolation for every sample (but already pre-solved).
// The coefficients for orders 0-3 originate from the SHORTEN codec:
// http://mi.eng.cam.ac.uk/reports/svr-ftp/auto-pdf/robinson_tr156.pdf page 4
// The coefficients for order 4 are undocumented in the original FLAC specification(s), but can now be found in
// https://datatracker.ietf.org/doc/html/draft-ietf-cellar-flac-03#section-10.2.5
// FIXME: Share this code with predict_fixed_lpc().
switch (subframe.order) {
case 0:
// s_0(t) = 0
for (u32 i = subframe.order; i < m_current_frame->sample_count; ++i)
decoded[i] += 0;
break;
case 1:
// s_1(t) = s(t-1)
for (u32 i = subframe.order; i < m_current_frame->sample_count; ++i)
decoded[i] += decoded[i - 1];
break;
case 2:
// s_2(t) = 2s(t-1) - s(t-2)
for (u32 i = subframe.order; i < m_current_frame->sample_count; ++i)
decoded[i] += 2 * decoded[i - 1] - decoded[i - 2];
break;
case 3:
// s_3(t) = 3s(t-1) - 3s(t-2) + s(t-3)
for (u32 i = subframe.order; i < m_current_frame->sample_count; ++i)
decoded[i] += 3 * decoded[i - 1] - 3 * decoded[i - 2] + decoded[i - 3];
break;
case 4:
// s_4(t) = 4s(t-1) - 6s(t-2) + 4s(t-3) - s(t-4)
for (u32 i = subframe.order; i < m_current_frame->sample_count; ++i)
decoded[i] += 4 * decoded[i - 1] - 6 * decoded[i - 2] + 4 * decoded[i - 3] - decoded[i - 4];
break;
default:
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), TRY(String::formatted("Unrecognized predictor order {}", subframe.order)) };
}
return decoded;
}
// 11.30. RESIDUAL
// Decode the residual, the "error" between the function approximation and the actual audio data
MaybeLoaderError FlacLoaderPlugin::decode_residual(Vector<i64>& decoded, FlacSubframeHeader& subframe, BigEndianInputBitStream& bit_input)
{
// 11.30.1. RESIDUAL_CODING_METHOD
auto residual_mode = static_cast<FlacResidualMode>(TRY(bit_input.read_bits<u8>(2)));
u8 partition_order = TRY(bit_input.read_bits<u8>(4));
size_t partitions = 1 << partition_order;
dbgln_if(AFLACLOADER_DEBUG, " {}-bit Rice partitions, {} total (order {})", residual_mode == FlacResidualMode::Rice4Bit ? "4"sv : "5"sv, partitions, partition_order);
if (partitions > m_current_frame->sample_count)
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Too many Rice partitions, each partition must contain at least one sample"_fly_string };
// “The partition order MUST be such that the block size is evenly divisible by the number of partitions.”
// FIXME: Check “The partition order also MUST be such that the (block size >> partition order) is larger than the predictor order.”
if (m_current_frame->sample_count % partitions != 0)
return LoaderError { LoaderError::Category::Format, TRY(m_stream->tell()), "Block size is not evenly divisible by number of partitions"_fly_string };
if (residual_mode == FlacResidualMode::Rice4Bit) {
// 11.30.2. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB
// decode a single Rice partition with four bits for the order k
for (size_t i = 0; i < partitions; ++i) {
// FIXME: Write into the decode buffer directly.
auto rice_partition = TRY(decode_rice_partition(4, partitions, i, subframe, bit_input));
decoded.extend(move(rice_partition));
}
} else if (residual_mode == FlacResidualMode::Rice5Bit) {
// 11.30.3. RESIDUAL_CODING_METHOD_PARTITIONED_EXP_GOLOMB2
// five bits equivalent
for (size_t i = 0; i < partitions; ++i) {
// FIXME: Write into the decode buffer directly.
auto rice_partition = TRY(decode_rice_partition(5, partitions, i, subframe, bit_input));
decoded.extend(move(rice_partition));
}
} else
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Reserved residual coding method"_fly_string };
return {};
}
// 11.30.2.1. EXP_GOLOMB_PARTITION and 11.30.3.1. EXP_GOLOMB2_PARTITION
// Decode a single Rice partition as part of the residual, every partition can have its own Rice parameter k
ALWAYS_INLINE ErrorOr<Vector<i64>, LoaderError> FlacLoaderPlugin::decode_rice_partition(u8 partition_type, u32 partitions, u32 partition_index, FlacSubframeHeader& subframe, BigEndianInputBitStream& bit_input)
{
// 11.30.2.2. EXP GOLOMB PARTITION ENCODING PARAMETER and 11.30.3.2. EXP-GOLOMB2 PARTITION ENCODING PARAMETER
u8 k = TRY(bit_input.read_bits<u8>(partition_type));
u32 residual_sample_count;
if (partitions == 0)
residual_sample_count = m_current_frame->sample_count - subframe.order;
else
residual_sample_count = m_current_frame->sample_count / partitions;
if (partition_index == 0) {
if (subframe.order > residual_sample_count)
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "First Rice partition must advertise more residuals than LPC order"_fly_string };
residual_sample_count -= subframe.order;
}
Vector<i64> rice_partition;
rice_partition.resize(residual_sample_count);
// escape code for unencoded binary partition
if (k == (1 << partition_type) - 1) {
u8 unencoded_bps = TRY(bit_input.read_bits<u8>(5));
if (unencoded_bps != 0) {
for (size_t r = 0; r < residual_sample_count; ++r) {
rice_partition[r] = AK::sign_extend(TRY(bit_input.read_bits<u32>(unencoded_bps)), unencoded_bps);
}
}
} else {
for (size_t r = 0; r < residual_sample_count; ++r) {
rice_partition[r] = TRY(decode_unsigned_exp_golomb(k, bit_input));
}
}
return rice_partition;
}
// Decode a single number encoded with Rice/Exponential-Golomb encoding (the unsigned variant)
ALWAYS_INLINE ErrorOr<i32> decode_unsigned_exp_golomb(u8 k, BigEndianInputBitStream& bit_input)
{
u8 q = 0;
while (TRY(bit_input.read_bit()) == 0)
++q;
// least significant bits (remainder)
u32 rem = TRY(bit_input.read_bits<u32>(k));
u32 value = q << k | rem;
return rice_to_signed(value);
}
ErrorOr<u64> read_utf8_char(BigEndianInputBitStream& input)
{
u64 character;
u8 start_byte = TRY(input.read_value<u8>());
// Signal byte is zero: ASCII character
if ((start_byte & 0b10000000) == 0) {
return start_byte;
} else if ((start_byte & 0b11000000) == 0b10000000) {
return Error::from_string_literal("Illegal continuation byte");
}
// This algorithm supports the theoretical max 0xFF start byte, which is not part of the regular UTF-8 spec.
u8 length = 1;
while (((start_byte << length) & 0b10000000) == 0b10000000)
++length;
// This is technically not spec-compliant, but if we take UTF-8 to its logical extreme,
// we can say 0xFF means there's 7 following continuation bytes and no data at all in the leading character.
if (length == 8) [[unlikely]] {
character = 0;
} else {
u8 bits_from_start_byte = 8 - (length + 1);
u8 start_byte_bitmask = AK::exp2(bits_from_start_byte) - 1;
character = start_byte_bitmask & start_byte;
}
for (u8 i = length - 1; i > 0; --i) {
u8 current_byte = TRY(input.read_value<u8>());
character = (character << 6) | (current_byte & 0b00111111);
}
return character;
}
i32 rice_to_signed(u32 x)
{
// positive numbers are even, negative numbers are odd
// bitmask for conditionally inverting the entire number, thereby "negating" it
i32 sign = -static_cast<i32>(x & 1);
// copies the sign's sign onto the actual magnitude of x
return static_cast<i32>(sign ^ (x >> 1));
}
}
