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ladybird/Userland/Libraries/LibAudio/FlacLoader.cpp
kleines Filmröllchen 59c7ce3d54 LibAudio: Prevent integer overflows in intermediate FLAC calculations 
Since we can have up to 32 bits of input data, multiplications may need
up to 63 bits. This was accounted for in some places, but by far not in
all, and oss-fuzz found multiple integer overflows. We now use i64 in
all of the decoding, since we need to rescale samples to float later on
anyways. If a final sample value ends up out of range (and the range can
be a maximum of 32 bits), we may get samples past 1, but that then is a
non-compliant input file, and using over-range samples (and most likely
clipping audio) is considerably less weird than overflowing and
glitching audio.
2023-07-04 12:47:08 +02:00

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/*
* Copyright (c) 2021, kleines Filmröllchen <filmroellchen@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Debug.h>
#include <AK/DeprecatedFlyString.h>
#include <AK/DeprecatedString.h>
#include <AK/FixedArray.h>
#include <AK/Format.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/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, LOADER_TRY(m_stream->tell()), DeprecatedString::formatted("FLAC header: {}", msg) }; \
} \
} while (0)
// Magic number
u32 flac = LOADER_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 = LOADER_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 = LOADER_TRY(streaminfo_data.read_bits<u16>(16));
FLAC_VERIFY(m_max_block_size >= 16, LoaderError::Category::Format, "Maximum block size");
m_min_frame_size = LOADER_TRY(streaminfo_data.read_bits<u32>(24));
m_max_frame_size = LOADER_TRY(streaminfo_data.read_bits<u32>(24));
m_sample_rate = LOADER_TRY(streaminfo_data.read_bits<u32>(20));
FLAC_VERIFY(m_sample_rate <= 655350, LoaderError::Category::Format, "Sample rate");
m_num_channels = LOADER_TRY(streaminfo_data.read_bits<u8>(3)) + 1; // 0 = one channel
m_bits_per_sample = LOADER_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 = LOADER_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());
LOADER_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 {}, 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), m_md5_checksum, m_data_start_location, total_meta_blocks, total_meta_blocks - meta_blocks_parsed);
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>(LOADER_TRY(picture_block_bytes.read_bits(32)));
auto const mime_string_length = LOADER_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, LOADER_TRY(m_stream->tell()), "Picture MIME type exceeds available data" };
// "The MIME type string, in printable ASCII characters 0x20-0x7E."
picture.mime_string = LOADER_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, LOADER_TRY(m_stream->tell()), "Picture MIME type is not ASCII in range 0x20 - 0x7E" };
}
auto const description_string_length = LOADER_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, LOADER_TRY(m_stream->tell()), "Picture description exceeds available data" };
picture.description_string = LOADER_TRY(String::from_stream(memory_stream, description_string_length));
picture.width = LOADER_TRY(picture_block_bytes.read_bits(32));
picture.height = LOADER_TRY(picture_block_bytes.read_bits(32));
picture.color_depth = LOADER_TRY(picture_block_bytes.read_bits(32));
picture.colors = LOADER_TRY(picture_block_bytes.read_bits(32));
auto const picture_size = LOADER_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" };
LOADER_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 = LOADER_TRY(seektable_bytes.read_bits<u64>(64));
u64 byte_offset = LOADER_TRY(seektable_bytes.read_bits<u64>(64));
// The sample count of a seek point is not relevant to us.
[[maybe_unused]] u16 sample_count = LOADER_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 = LOADER_TRY(bit_input.read_bit());
// The block type enum constants agree with the specification
FlacMetadataBlockType type = (FlacMetadataBlockType)LOADER_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 = LOADER_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 = LOADER_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();
LOADER_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);
auto const seek_tolerance = (seek_tolerance_ms * m_sample_rate) / 1000;
// No seektable or no fitting entry: Perform normal forward read
if (!maybe_target_seekpoint.has_value()) {
if (sample_index < m_loaded_samples) {
LOADER_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): not seeking", sample_index - m_loaded_samples);
return {};
}
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, DeprecatedString::formatted("Invalid seek position {}", position) };
m_loaded_samples = target_seekpoint.sample_index;
}
// Skip frames until we're within the seek tolerance.
while (sample_index - m_loaded_samples > seek_tolerance) {
(void)TRY(next_frame());
m_loaded_samples += m_current_frame->sample_count;
}
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 distance_to_previous_seekpoint = sample_index - m_seektable.seek_point_before(sample_index).value_or({ 0, 0 }).sample_index;
// 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() || remaining_samples <= 0)
return Vector<FixedArray<Sample>> {};
size_t samples_to_read = min(samples_to_read_from_input, remaining_samples);
Vector<FixedArray<Sample>> frames;
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), DeprecatedString::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 checksum_stream = TRY(try_make<Crypto::Checksum::ChecksummingStream<FlacFrameHeaderCRC>>(MaybeOwned<Stream>(*m_stream)));
BigEndianInputBitStream bit_stream { MaybeOwned<Stream> { *checksum_stream } };
// TODO: Check the CRC-16 checksum by keeping track of read data.
// 11.22. FRAME_HEADER
u16 sync_code = LOADER_TRY(bit_stream.read_bits<u16>(14));
FLAC_VERIFY(sync_code == 0b11111111111110, LoaderError::Category::Format, "Sync code");
bool reserved_bit = LOADER_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 = LOADER_TRY(bit_stream.read_bit());
u32 sample_count = TRY(convert_sample_count_code(LOADER_TRY(bit_stream.read_bits<u8>(4))));
u32 frame_sample_rate = TRY(convert_sample_rate_code(LOADER_TRY(bit_stream.read_bits<u8>(4))));
u8 channel_type_num = LOADER_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(LOADER_TRY(bit_stream.read_bits<u8>(3))));
reserved_bit = LOADER_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 = LOADER_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 = LOADER_TRY(bit_stream.read_bits<u32>(8)) + 1;
} else if (sample_count == FLAC_BLOCKSIZE_AT_END_OF_HEADER_16) {
sample_count = LOADER_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 = LOADER_TRY(bit_stream.read_bits<u32>(8)) * 1000;
} else if (frame_sample_rate == FLAC_SAMPLERATE_AT_END_OF_HEADER_16) {
frame_sample_rate = LOADER_TRY(bit_stream.read_bits<u32>(16));
} else if (frame_sample_rate == FLAC_SAMPLERATE_AT_END_OF_HEADER_16X10) {
frame_sample_rate = LOADER_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_checksum = checksum_stream->digest();
// 11.22.11. FRAME CRC
u8 specified_checksum = LOADER_TRY(bit_stream.read_bits<u8>(8));
VERIFY(bit_stream.is_aligned_to_byte_boundary());
if (specified_checksum != calculated_checksum)
dbgln("FLAC frame {}: Calculated header checksum {:02x} is different from specified checksum {:02x}", m_current_sample_or_frame, calculated_checksum, specified_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_checksum, specified_checksum != calculated_checksum ? " (checksum error)"sv : ""sv);
m_current_frame = FlacFrameHeader {
sample_count,
frame_sample_rate,
channel_type,
bit_depth,
specified_checksum,
};
u8 subframe_count = frame_channel_type_to_channel_count(channel_type);
Vector<Vector<i64>> current_subframes;
current_subframes.ensure_capacity(subframe_count);
for (u8 i = 0; i < subframe_count; ++i) {
FlacSubframeHeader new_subframe = TRY(next_subframe_header(bit_stream, i));
Vector<i64> subframe_samples = TRY(parse_subframe(new_subframe, bit_stream));
VERIFY(subframe_samples.size() == m_current_frame->sample_count);
current_subframes.unchecked_append(move(subframe_samples));
}
// 11.2. Overview ("The audio data is composed of...")
bit_stream.align_to_byte_boundary();
// 11.23. FRAME_FOOTER
// TODO: check checksum, see above
[[maybe_unused]] u16 footer_checksum = LOADER_TRY(bit_stream.read_bits<u16>(16));
dbgln_if(AFLACLOADER_DEBUG, "Subframe footer checksum: {}", footer_checksum);
float sample_rescale = 1 / static_cast<float>(1 << (m_current_frame->bit_depth - 1));
dbgln_if(AFLACLOADER_DEBUG, "Sample rescaled from {} bits: factor {:.8f}", m_current_frame->bit_depth, sample_rescale);
FixedArray<Sample> samples = TRY(FixedArray<Sample>::create(m_current_frame->sample_count));
switch (channel_type) {
case FlacFrameChannelType::Mono:
for (size_t i = 0; i < m_current_frame->sample_count; ++i)
samples[i] = Sample { static_cast<float>(current_subframes[0][i]) * sample_rescale };
break;
case FlacFrameChannelType::Stereo:
// TODO mix together surround channels on each side?
case FlacFrameChannelType::StereoCenter:
case FlacFrameChannelType::Surround4p0:
case FlacFrameChannelType::Surround5p0:
case FlacFrameChannelType::Surround5p1:
case FlacFrameChannelType::Surround6p1:
case FlacFrameChannelType::Surround7p1:
for (size_t i = 0; i < m_current_frame->sample_count; ++i)
samples[i] = { static_cast<float>(current_subframes[0][i]) * sample_rescale, static_cast<float>(current_subframes[1][i]) * sample_rescale };
break;
case FlacFrameChannelType::LeftSideStereo:
// 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>(current_subframes[0][i]) * sample_rescale,
static_cast<float>(current_subframes[0][i] - current_subframes[1][i]) * sample_rescale };
}
break;
case FlacFrameChannelType::RightSideStereo:
// 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>(current_subframes[1][i] + current_subframes[0][i]) * sample_rescale,
static_cast<float>(current_subframes[1][i]) * sample_rescale };
}
break;
case FlacFrameChannelType::MidSideStereo:
// channels are mid (0) and side (1)
for (size_t i = 0; i < current_subframes[0].size(); ++i) {
i64 mid = current_subframes[0][i];
i64 side = current_subframes[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" };
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" };
}
}
// 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" };
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), DeprecatedString::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 (LOADER_TRY(bit_stream.read_bit()) != 0)
return LoaderError { LoaderError::Category::Format, static_cast<size_t>(m_current_sample_or_frame), "Zero bit padding" };
// 11.25.1. SUBFRAME TYPE
u8 subframe_code = LOADER_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" };
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 = LOADER_TRY(bit_stream.read_bit());
u8 k = 0;
if (has_wasted_bits) {
bool current_k_bit = 0;
do {
current_k_bit = LOADER_TRY(bit_stream.read_bit());
++k;
} while (current_k_bit != 1);
}
return FlacSubframeHeader {
subframe_type,
order,
k,
bits_per_sample
};
}
ErrorOr<Vector<i64>, LoaderError> FlacLoaderPlugin::parse_subframe(FlacSubframeHeader& subframe_header, BigEndianInputBitStream& bit_input)
{
Vector<i64> samples;
switch (subframe_header.type) {
case FlacSubframeType::Constant: {
// 11.26. SUBFRAME_CONSTANT
u64 constant_value = LOADER_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);
samples.ensure_capacity(m_current_frame->sample_count);
VERIFY(subframe_header.bits_per_sample - subframe_header.wasted_bits_per_sample != 0);
i64 constant = 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);
samples = TRY(decode_custom_lpc(subframe_header, bit_input));
break;
}
default:
return LoaderError { LoaderError::Category::Unimplemented, static_cast<size_t>(m_current_sample_or_frame), "Unhandled FLAC subframe type" };
}
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)
return samples;
ResampleHelper<i64> resampler(m_current_frame->sample_rate, m_sample_rate);
return resampler.resample(samples);
}
// 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);
VERIFY(subframe.bits_per_sample - subframe.wasted_bits_per_sample != 0);
for (size_t i = 0; i < m_current_frame->sample_count; ++i) {
decoded.unchecked_append(sign_extend(
LOADER_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<Vector<i64>, LoaderError> FlacLoaderPlugin::decode_custom_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" };
Vector<i64> decoded;
decoded.ensure_capacity(m_current_frame->sample_count);
VERIFY(subframe.bits_per_sample - subframe.wasted_bits_per_sample != 0);
// warm-up samples
for (auto i = 0; i < subframe.order; ++i) {
decoded.unchecked_append(sign_extend(
LOADER_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 = LOADER_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" };
lpc_precision += 1;
// shift needed on the data (signed!)
i8 lpc_shift = static_cast<i8>(sign_extend(LOADER_TRY(bit_input.read_bits<u8>(5)), 5));
Vector<i64> coefficients;
coefficients.ensure_capacity(subframe.order);
// read coefficients
for (auto i = 0; i < subframe.order; ++i) {
u64 raw_coefficient = LOADER_TRY(bit_input.read_bits<u64>(lpc_precision));
i64 coefficient = static_cast<i64>(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)
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.
// 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 += static_cast<i64>(coefficients[t]) * static_cast<i64>(decoded[i - t - 1]);
}
decoded[i] += sample >> lpc_shift;
}
return decoded;
}
// 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" };
Vector<i64> decoded;
decoded.ensure_capacity(m_current_frame->sample_count);
VERIFY(subframe.bits_per_sample - subframe.wasted_bits_per_sample != 0);
// warm-up samples
for (auto i = 0; i < subframe.order; ++i) {
decoded.unchecked_append(sign_extend(
LOADER_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", decoded.size(), subframe.order);
// 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
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), DeprecatedString::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>(LOADER_TRY(bit_input.read_bits<u8>(2)));
u8 partition_order = LOADER_TRY(bit_input.read_bits<u8>(4));
size_t partitions = 1 << partition_order;
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) {
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) {
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" };
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 = LOADER_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)
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 = LOADER_TRY(bit_input.read_bits<u8>(5));
for (size_t r = 0; r < residual_sample_count; ++r) {
rice_partition[r] = LOADER_TRY(bit_input.read_bits<u8>(unencoded_bps));
}
} else {
for (size_t r = 0; r < residual_sample_count; ++r) {
rice_partition[r] = LOADER_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 is too good and supports the theoretical max 0xFF start byte
u8 length = 1;
while (((start_byte << length) & 0b10000000) == 0b10000000)
++length;
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;
}
i64 sign_extend(u32 n, u8 size)
{
// negative
if ((n & (1 << (size - 1))) > 0) {
return static_cast<i64>(n | (0xffffffff << size));
}
// positive
return n;
}
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));
}
}
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