14d330faba
Decoding the residual in FLAC subframes is by far the most I/O-heavy operation in FLAC decoding, as the residual data makes up the majority of subframe data in LPC subframes. As the residual consists of many Rice-encoded numbers with different bit sizes for differently large numbers, the residual decoder frequently reads only one or two bytes at a time. As we use a normal FileInputStream, that directly translates to many calls to the read() syscall. We can see that the I/O overhead while FLAC decoding is quite large, and much time is spent in the read() syscall's kernel code. This is optimized by using a Buffered<FileInputStream> instead, leading to 4K blocks being read at once and a large reduction in I/O overhead. Benchmarking with the new abench utility gives a 15-20% speedup on identical files, usually pushing FLAC decoding to 10-15x realtime speed on common sample rates.
881 lines
32 KiB
C++
881 lines
32 KiB
C++
/*
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* Copyright (c) 2021, kleines Filmröllchen <malu.bertsch@gmail.com>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include "FlacLoader.h"
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#include "Buffer.h"
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#include <AK/BitStream.h>
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#include <AK/Debug.h>
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#include <AK/FlyString.h>
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#include <AK/Format.h>
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#include <AK/Math.h>
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#include <AK/ScopeGuard.h>
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#include <AK/Stream.h>
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#include <AK/String.h>
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#include <AK/StringBuilder.h>
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#include <LibCore/File.h>
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#include <LibCore/FileStream.h>
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namespace Audio {
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FlacLoaderPlugin::FlacLoaderPlugin(StringView path)
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: m_file(Core::File::construct(path))
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{
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if (!m_file->open(Core::OpenMode::ReadOnly)) {
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m_error_string = String::formatted("Can't open file: {}", m_file->error_string());
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return;
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}
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auto maybe_stream = Core::InputFileStream::open_buffered(path);
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if (maybe_stream.is_error()) {
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m_error_string = "Can't open file stream";
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return;
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}
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m_stream = make<FlacInputStream>(maybe_stream.release_value());
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if (!m_stream) {
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m_error_string = "Can't open file stream";
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return;
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}
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m_valid = parse_header();
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if (!m_valid)
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return;
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reset();
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if (!m_valid)
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return;
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}
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FlacLoaderPlugin::FlacLoaderPlugin(const ByteBuffer& buffer)
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{
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m_stream = make<FlacInputStream>(InputMemoryStream(buffer));
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if (!m_stream) {
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m_error_string = String::formatted("Can't open memory stream");
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return;
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}
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m_valid = parse_header();
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if (!m_valid)
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return;
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reset();
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if (!m_valid)
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return;
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}
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bool FlacLoaderPlugin::sniff()
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{
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return m_valid;
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}
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bool FlacLoaderPlugin::parse_header()
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{
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bool ok = true;
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InputBitStream bit_input = [&]() -> InputBitStream {
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if (m_file) {
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return InputBitStream(m_stream->get<Buffered<Core::InputFileStream>>());
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}
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return InputBitStream(m_stream->get<InputMemoryStream>());
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}();
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ScopeGuard clear_bit_input_errors([&bit_input] { bit_input.handle_any_error(); });
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#define CHECK_OK(msg) \
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do { \
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if (!ok) { \
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m_stream->handle_any_error(); \
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m_error_string = String::formatted("Parsing failed: {}", msg); \
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return {}; \
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} \
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} while (0)
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// Magic number
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u32 flac = static_cast<u32>(bit_input.read_bits_big_endian(32));
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m_data_start_location += 4;
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ok = ok && flac == 0x664C6143; // "flaC"
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CHECK_OK("FLAC magic number");
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// Receive the streaminfo block
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FlacRawMetadataBlock streaminfo = next_meta_block(bit_input);
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// next_meta_block sets the error string if something goes wrong
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ok = ok && m_error_string.is_empty();
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CHECK_OK(m_error_string);
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ok = ok && (streaminfo.type == FlacMetadataBlockType::STREAMINFO);
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CHECK_OK("First block type");
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InputMemoryStream streaminfo_data_memory(streaminfo.data.bytes());
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InputBitStream streaminfo_data(streaminfo_data_memory);
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ScopeGuard clear_streaminfo_errors([&streaminfo_data] { streaminfo_data.handle_any_error(); });
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// STREAMINFO block
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m_min_block_size = static_cast<u16>(streaminfo_data.read_bits_big_endian(16));
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ok = ok && (m_min_block_size >= 16);
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CHECK_OK("Minimum block size");
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m_max_block_size = static_cast<u16>(streaminfo_data.read_bits_big_endian(16));
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ok = ok && (m_max_block_size >= 16);
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CHECK_OK("Maximum block size");
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m_min_frame_size = static_cast<u32>(streaminfo_data.read_bits_big_endian(24));
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m_max_frame_size = static_cast<u32>(streaminfo_data.read_bits_big_endian(24));
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m_sample_rate = static_cast<u32>(streaminfo_data.read_bits_big_endian(20));
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ok = ok && (m_sample_rate <= 655350);
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CHECK_OK("Sample rate");
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m_num_channels = static_cast<u8>(streaminfo_data.read_bits_big_endian(3)) + 1; // 0 ^= one channel
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u8 bits_per_sample = static_cast<u8>(streaminfo_data.read_bits_big_endian(5)) + 1;
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if (bits_per_sample == 8) {
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// FIXME: Signed/Unsigned issues?
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m_sample_format = PcmSampleFormat::Uint8;
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} else if (bits_per_sample == 16) {
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m_sample_format = PcmSampleFormat::Int16;
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} else if (bits_per_sample == 24) {
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m_sample_format = PcmSampleFormat::Int24;
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} else if (bits_per_sample == 32) {
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m_sample_format = PcmSampleFormat::Int32;
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} else {
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ok = false;
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CHECK_OK("Sample bit depth");
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}
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m_total_samples = static_cast<u64>(streaminfo_data.read_bits_big_endian(36));
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ok = ok && (m_total_samples > 0);
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CHECK_OK("Number of samples");
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// Parse checksum into a buffer first
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Array<u8, 128 / 8> md5_checksum;
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auto md5_bytes_read = streaminfo_data.read(md5_checksum);
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ok = ok && (md5_bytes_read == md5_checksum.size());
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CHECK_OK("MD5 Checksum");
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md5_checksum.span().copy_to({ m_md5_checksum, sizeof(m_md5_checksum) });
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// Parse other blocks
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// TODO: For a simple first implementation, all other blocks are skipped as allowed by the FLAC specification.
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// Especially the SEEKTABLE block may become useful in a more sophisticated version.
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[[maybe_unused]] u16 meta_blocks_parsed = 1;
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[[maybe_unused]] u16 total_meta_blocks = meta_blocks_parsed;
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FlacRawMetadataBlock block = streaminfo;
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while (!block.is_last_block) {
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block = next_meta_block(bit_input);
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++total_meta_blocks;
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ok = ok && m_error_string.is_empty();
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CHECK_OK(m_error_string);
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}
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if (m_stream->handle_any_error()) {
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m_error_string = "Parsing failed: Stream";
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return false;
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}
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if constexpr (AFLACLOADER_DEBUG) {
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// HACK: u128 should be able to format itself
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StringBuilder checksum_string;
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for (unsigned int i = 0; i < md5_checksum.size(); ++i) {
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checksum_string.appendff("{:0X}", md5_checksum[i]);
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}
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dbgln("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<double>(m_total_samples) / static_cast<double>(m_sample_rate), checksum_string.to_string(), m_data_start_location, total_meta_blocks, total_meta_blocks - meta_blocks_parsed);
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}
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return true;
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#undef CHECK_OK
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}
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FlacRawMetadataBlock FlacLoaderPlugin::next_meta_block(InputBitStream& bit_input)
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{
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#define CHECK_IO_ERROR() \
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do { \
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if (bit_input.handle_any_error()) { \
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m_error_string = "Read error"; \
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return FlacRawMetadataBlock {}; \
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} \
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} while (0)
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bool is_last_block = bit_input.read_bit_big_endian();
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CHECK_IO_ERROR();
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// The block type enum constants agree with the specification
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FlacMetadataBlockType type = (FlacMetadataBlockType)bit_input.read_bits_big_endian(7);
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CHECK_IO_ERROR();
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if (type == FlacMetadataBlockType::INVALID) {
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m_error_string = "Invalid metadata block";
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return FlacRawMetadataBlock {};
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}
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m_data_start_location += 1;
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u32 block_length = static_cast<u32>(bit_input.read_bits_big_endian(24));
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m_data_start_location += 3;
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CHECK_IO_ERROR();
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auto block_data_result = ByteBuffer::create_uninitialized(block_length);
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if (!block_data_result.has_value()) {
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m_error_string = "Out of memory";
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return FlacRawMetadataBlock {};
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}
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auto block_data = block_data_result.release_value();
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// Reads exactly the bytes necessary into the Bytes container
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bit_input.read(block_data);
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m_data_start_location += block_length;
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CHECK_IO_ERROR();
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return FlacRawMetadataBlock {
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is_last_block,
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type,
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block_length,
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block_data,
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};
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#undef CHECK_IO_ERROR
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}
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void FlacLoaderPlugin::reset()
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{
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seek(m_data_start_location);
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m_current_frame.clear();
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}
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void FlacLoaderPlugin::seek(const int position)
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{
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if (!m_stream->seek(position)) {
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m_error_string = String::formatted("Invalid seek position {}", position);
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m_valid = false;
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}
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}
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RefPtr<Buffer> FlacLoaderPlugin::get_more_samples(size_t max_bytes_to_read_from_input)
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{
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Vector<Sample> samples;
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ssize_t remaining_samples = static_cast<ssize_t>(m_total_samples - m_loaded_samples);
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if (remaining_samples <= 0) {
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return nullptr;
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}
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size_t samples_to_read = min(max_bytes_to_read_from_input, remaining_samples);
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while (samples_to_read > 0) {
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if (!m_current_frame.has_value()) {
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next_frame();
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if (!m_error_string.is_empty()) {
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m_error_string = String::formatted("Frame parsing error: {}", m_error_string);
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return nullptr;
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}
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}
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samples.append(m_current_frame_data.take_first());
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if (m_current_frame_data.is_empty()) {
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m_current_frame.clear();
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}
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--samples_to_read;
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}
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m_loaded_samples += samples.size();
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return Buffer::create_with_samples(move(samples));
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}
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void FlacLoaderPlugin::next_frame()
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{
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bool ok = true;
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InputBitStream bit_stream = m_stream->bit_stream();
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#define CHECK_OK(msg) \
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do { \
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if (!ok) { \
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m_error_string = String::formatted("Frame parsing failed: {}", msg); \
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bit_stream.align_to_byte_boundary(); \
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bit_stream.handle_any_error(); \
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dbgln_if(AFLACLOADER_DEBUG, "Crash in FLAC loader: next bytes are {:x}", bit_stream.read_bits_big_endian(32)); \
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return; \
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} \
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} while (0)
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#define CHECK_ERROR_STRING \
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do { \
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if (!m_error_string.is_null() && !m_error_string.is_empty()) { \
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ok = false; \
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CHECK_OK(m_error_string); \
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} \
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} while (0)
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// TODO: Check the CRC-16 checksum (and others) by keeping track of read data
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// FLAC frame sync code starts header
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u16 sync_code = static_cast<u16>(bit_stream.read_bits_big_endian(14));
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ok = ok && (sync_code == 0b11111111111110);
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CHECK_OK("Sync code");
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bool reserved_bit = bit_stream.read_bit_big_endian();
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ok = ok && (reserved_bit == 0);
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CHECK_OK("Reserved frame header bit");
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[[maybe_unused]] bool blocking_strategy = bit_stream.read_bit_big_endian();
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u32 sample_count = convert_sample_count_code(static_cast<u8>(bit_stream.read_bits_big_endian(4)));
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CHECK_ERROR_STRING;
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u32 frame_sample_rate = convert_sample_rate_code(static_cast<u8>(bit_stream.read_bits_big_endian(4)));
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CHECK_ERROR_STRING;
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u8 channel_type_num = static_cast<u8>(bit_stream.read_bits_big_endian(4));
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if (channel_type_num >= 0b1011) {
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ok = false;
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CHECK_OK("Channel assignment");
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}
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FlacFrameChannelType channel_type = (FlacFrameChannelType)channel_type_num;
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PcmSampleFormat bit_depth = convert_bit_depth_code(static_cast<u8>(bit_stream.read_bits_big_endian(3)));
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CHECK_ERROR_STRING;
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reserved_bit = bit_stream.read_bit_big_endian();
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ok = ok && (reserved_bit == 0);
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CHECK_OK("Reserved frame header end bit");
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// FIXME: sample number can be 8-56 bits, frame number can be 8-48 bits
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m_current_sample_or_frame = read_utf8_char(bit_stream);
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// Conditional header variables
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if (sample_count == FLAC_BLOCKSIZE_AT_END_OF_HEADER_8) {
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sample_count = static_cast<u32>(bit_stream.read_bits_big_endian(8)) + 1;
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} else if (sample_count == FLAC_BLOCKSIZE_AT_END_OF_HEADER_16) {
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sample_count = static_cast<u32>(bit_stream.read_bits_big_endian(16)) + 1;
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}
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if (frame_sample_rate == FLAC_SAMPLERATE_AT_END_OF_HEADER_8) {
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frame_sample_rate = static_cast<u32>(bit_stream.read_bits_big_endian(8)) * 1000;
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} else if (frame_sample_rate == FLAC_SAMPLERATE_AT_END_OF_HEADER_16) {
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frame_sample_rate = static_cast<u32>(bit_stream.read_bits_big_endian(16));
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} else if (frame_sample_rate == FLAC_SAMPLERATE_AT_END_OF_HEADER_16X10) {
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frame_sample_rate = static_cast<u32>(bit_stream.read_bits_big_endian(16)) * 10;
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}
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// TODO: check header checksum, see above
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[[maybe_unused]] u8 checksum = static_cast<u8>(bit_stream.read_bits(8));
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dbgln_if(AFLACLOADER_DEBUG, "Frame: {} samples, {}bit {}Hz, channeltype {:x}, {} number {}, header checksum {}", sample_count, pcm_bits_per_sample(bit_depth), frame_sample_rate, channel_type_num, blocking_strategy ? "sample" : "frame", m_current_sample_or_frame, checksum);
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m_current_frame = FlacFrameHeader {
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sample_count,
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frame_sample_rate,
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channel_type,
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bit_depth,
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};
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u8 subframe_count = frame_channel_type_to_channel_count(channel_type);
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Vector<Vector<i32>> current_subframes;
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current_subframes.ensure_capacity(subframe_count);
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for (u8 i = 0; i < subframe_count; ++i) {
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FlacSubframeHeader new_subframe = next_subframe_header(bit_stream, i);
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CHECK_ERROR_STRING;
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Vector<i32> subframe_samples = parse_subframe(new_subframe, bit_stream);
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CHECK_ERROR_STRING;
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current_subframes.append(move(subframe_samples));
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}
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bit_stream.align_to_byte_boundary();
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// TODO: check checksum, see above
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[[maybe_unused]] u16 footer_checksum = static_cast<u16>(bit_stream.read_bits_big_endian(16));
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Vector<i32> left;
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Vector<i32> right;
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switch (channel_type) {
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case FlacFrameChannelType::Mono:
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left = right = current_subframes[0];
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break;
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case FlacFrameChannelType::Stereo:
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// TODO mix together surround channels on each side?
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case FlacFrameChannelType::StereoCenter:
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case FlacFrameChannelType::Surround4p0:
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case FlacFrameChannelType::Surround5p0:
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case FlacFrameChannelType::Surround5p1:
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case FlacFrameChannelType::Surround6p1:
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case FlacFrameChannelType::Surround7p1:
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left = current_subframes[0];
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right = current_subframes[1];
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break;
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case FlacFrameChannelType::LeftSideStereo:
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// channels are left (0) and side (1)
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left = current_subframes[0];
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right.ensure_capacity(left.size());
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for (size_t i = 0; i < left.size(); ++i) {
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// right = left - side
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right.unchecked_append(left[i] - current_subframes[1][i]);
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}
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break;
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case FlacFrameChannelType::RightSideStereo:
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// channels are side (0) and right (1)
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right = current_subframes[1];
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left.ensure_capacity(right.size());
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for (size_t i = 0; i < right.size(); ++i) {
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// left = right + side
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left.unchecked_append(right[i] + current_subframes[0][i]);
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}
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break;
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case FlacFrameChannelType::MidSideStereo:
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// channels are mid (0) and side (1)
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left.ensure_capacity(current_subframes[0].size());
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right.ensure_capacity(current_subframes[0].size());
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for (size_t i = 0; i < current_subframes[0].size(); ++i) {
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i64 mid = current_subframes[0][i];
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i64 side = current_subframes[1][i];
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mid *= 2;
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// prevent integer division errors
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left.unchecked_append(static_cast<i32>((mid + side) / 2));
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right.unchecked_append(static_cast<i32>((mid - side) / 2));
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}
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break;
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}
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VERIFY(left.size() == right.size());
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double sample_rescale = static_cast<double>(1 << (pcm_bits_per_sample(m_current_frame->bit_depth) - 1));
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dbgln_if(AFLACLOADER_DEBUG, "Sample rescaled from {} bits: factor {:.1f}", pcm_bits_per_sample(m_current_frame->bit_depth), sample_rescale);
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m_current_frame_data.clear_with_capacity();
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m_current_frame_data.ensure_capacity(left.size());
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// zip together channels
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for (size_t i = 0; i < left.size(); ++i) {
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Sample frame = { left[i] / sample_rescale, right[i] / sample_rescale };
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m_current_frame_data.unchecked_append(frame);
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}
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#undef CHECK_OK
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#undef CHECK_ERROR_STRING
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}
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u32 FlacLoaderPlugin::convert_sample_count_code(u8 sample_count_code)
|
|
{
|
|
// single codes
|
|
switch (sample_count_code) {
|
|
case 0:
|
|
m_error_string = "Reserved block size";
|
|
return 0;
|
|
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);
|
|
}
|
|
|
|
u32 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:
|
|
m_error_string = "Invalid sample rate code";
|
|
return 0;
|
|
}
|
|
}
|
|
|
|
PcmSampleFormat FlacLoaderPlugin::convert_bit_depth_code(u8 bit_depth_code)
|
|
{
|
|
switch (bit_depth_code) {
|
|
case 0:
|
|
return m_sample_format;
|
|
case 1:
|
|
return PcmSampleFormat::Uint8;
|
|
case 4:
|
|
return PcmSampleFormat::Int16;
|
|
case 6:
|
|
return PcmSampleFormat::Int24;
|
|
case 3:
|
|
case 7:
|
|
m_error_string = "Reserved sample size";
|
|
return PcmSampleFormat::Float64;
|
|
default:
|
|
m_error_string = String::formatted("Unsupported sample size {}", bit_depth_code);
|
|
return PcmSampleFormat::Float64;
|
|
}
|
|
}
|
|
|
|
u8 frame_channel_type_to_channel_count(FlacFrameChannelType channel_type)
|
|
{
|
|
if (channel_type <= 7)
|
|
return channel_type + 1;
|
|
return 2;
|
|
}
|
|
|
|
FlacSubframeHeader FlacLoaderPlugin::next_subframe_header(InputBitStream& bit_stream, u8 channel_index)
|
|
{
|
|
u8 bits_per_sample = static_cast<u16>(pcm_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 LeftSideStereo:
|
|
case MidSideStereo:
|
|
if (channel_index == 1) {
|
|
++bits_per_sample;
|
|
}
|
|
break;
|
|
case RightSideStereo:
|
|
if (channel_index == 0) {
|
|
++bits_per_sample;
|
|
}
|
|
break;
|
|
// "normal" channel types
|
|
default:
|
|
break;
|
|
}
|
|
|
|
// zero-bit padding
|
|
if (bit_stream.read_bit_big_endian() != 0) {
|
|
m_error_string = "Zero bit padding";
|
|
return {};
|
|
};
|
|
|
|
// subframe type (encoding)
|
|
u8 subframe_code = static_cast<u8>(bit_stream.read_bits_big_endian(6));
|
|
if ((subframe_code >= 0b000010 && subframe_code <= 0b000111) || (subframe_code > 0b001100 && subframe_code < 0b100000)) {
|
|
m_error_string = "Subframe type";
|
|
return {};
|
|
}
|
|
|
|
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;
|
|
}
|
|
|
|
// wasted bits per sample (unary encoding)
|
|
bool has_wasted_bits = bit_stream.read_bit_big_endian();
|
|
u8 k = 0;
|
|
if (has_wasted_bits) {
|
|
bool current_k_bit = 0;
|
|
do {
|
|
current_k_bit = bit_stream.read_bit_big_endian();
|
|
++k;
|
|
} while (current_k_bit != 1);
|
|
}
|
|
|
|
return FlacSubframeHeader {
|
|
subframe_type,
|
|
order,
|
|
k,
|
|
bits_per_sample
|
|
};
|
|
}
|
|
|
|
Vector<i32> FlacLoaderPlugin::parse_subframe(FlacSubframeHeader& subframe_header, InputBitStream& bit_input)
|
|
{
|
|
Vector<i32> samples;
|
|
|
|
switch (subframe_header.type) {
|
|
case FlacSubframeType::Constant: {
|
|
u64 constant_value = bit_input.read_bits_big_endian(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);
|
|
i32 constant = sign_extend(static_cast<u32>(constant_value), subframe_header.bits_per_sample - subframe_header.wasted_bits_per_sample);
|
|
for (u32 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 = decode_fixed_lpc(subframe_header, bit_input);
|
|
break;
|
|
}
|
|
case FlacSubframeType::Verbatim: {
|
|
dbgln_if(AFLACLOADER_DEBUG, "Verbatim subframe");
|
|
samples = decode_verbatim(subframe_header, bit_input);
|
|
break;
|
|
}
|
|
case FlacSubframeType::LPC: {
|
|
dbgln_if(AFLACLOADER_DEBUG, "Custom LPC subframe order {}", subframe_header.order);
|
|
samples = decode_custom_lpc(subframe_header, bit_input);
|
|
break;
|
|
}
|
|
default:
|
|
m_error_string = "Unhandled FLAC subframe type";
|
|
return {};
|
|
}
|
|
if (!m_error_string.is_empty()) {
|
|
return {};
|
|
}
|
|
|
|
for (size_t i = 0; i < samples.size(); ++i) {
|
|
samples[i] <<= subframe_header.wasted_bits_per_sample;
|
|
}
|
|
|
|
ResampleHelper<i32> resampler(m_current_frame->sample_rate, m_sample_rate);
|
|
return resampler.resample(samples);
|
|
}
|
|
|
|
// Decode a subframe that isn't actually encoded, usually seen in random data
|
|
Vector<i32> FlacLoaderPlugin::decode_verbatim(FlacSubframeHeader& subframe, InputBitStream& bit_input)
|
|
{
|
|
Vector<i32> 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(
|
|
static_cast<u32>(bit_input.read_bits_big_endian(subframe.bits_per_sample - subframe.wasted_bits_per_sample)),
|
|
subframe.bits_per_sample - subframe.wasted_bits_per_sample));
|
|
}
|
|
|
|
return decoded;
|
|
}
|
|
|
|
// Decode a subframe encoded with a custom linear predictor coding, i.e. the subframe provides the polynomial order and coefficients
|
|
Vector<i32> FlacLoaderPlugin::decode_custom_lpc(FlacSubframeHeader& subframe, InputBitStream& bit_input)
|
|
{
|
|
Vector<i32> 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(
|
|
static_cast<u32>(bit_input.read_bits_big_endian(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 = static_cast<u8>(bit_input.read_bits_big_endian(4));
|
|
if (lpc_precision == 0b1111) {
|
|
m_error_string = "Invalid linear predictor coefficient precision";
|
|
return {};
|
|
}
|
|
lpc_precision += 1;
|
|
|
|
// shift needed on the data (signed!)
|
|
i8 lpc_shift = sign_extend(static_cast<u32>(bit_input.read_bits_big_endian(5)), 5);
|
|
|
|
Vector<i32> coefficients;
|
|
coefficients.ensure_capacity(subframe.order);
|
|
// read coefficients
|
|
for (auto i = 0; i < subframe.order; ++i) {
|
|
u32 raw_coefficient = static_cast<u32>(bit_input.read_bits_big_endian(lpc_precision));
|
|
i32 coefficient = static_cast<i32>(sign_extend(raw_coefficient, lpc_precision));
|
|
coefficients.unchecked_append(coefficient);
|
|
}
|
|
|
|
dbgln_if(AFLACLOADER_DEBUG, "{}-bit {} shift coefficients: {}", lpc_precision, lpc_shift, coefficients);
|
|
|
|
// decode residual
|
|
decoded = 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 apruptly stops intermittently (at the end of a frame).
|
|
// The simple fix of course is to do intermediate computations in 64 bits.
|
|
sample += static_cast<i64>(coefficients[t]) * static_cast<i64>(decoded[i - t - 1]);
|
|
}
|
|
decoded[i] += sample >> lpc_shift;
|
|
}
|
|
|
|
return decoded;
|
|
}
|
|
|
|
// Decode a subframe encoded with one of the fixed linear predictor codings
|
|
Vector<i32> FlacLoaderPlugin::decode_fixed_lpc(FlacSubframeHeader& subframe, InputBitStream& bit_input)
|
|
{
|
|
Vector<i32> 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(
|
|
static_cast<u32>(bit_input.read_bits_big_endian(subframe.bits_per_sample - subframe.wasted_bits_per_sample)),
|
|
subframe.bits_per_sample - subframe.wasted_bits_per_sample));
|
|
}
|
|
|
|
decode_residual(decoded, subframe, bit_input);
|
|
if (!m_error_string.is_empty())
|
|
return {};
|
|
dbgln_if(AFLACLOADER_DEBUG, "decoded length {}, {} order predictor", decoded.size(), subframe.order);
|
|
|
|
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:
|
|
m_error_string = String::formatted("Unrecognized predictor order {}", subframe.order);
|
|
break;
|
|
}
|
|
return decoded;
|
|
}
|
|
|
|
// Decode the residual, the "error" between the function approximation and the actual audio data
|
|
Vector<i32> FlacLoaderPlugin::decode_residual(Vector<i32>& decoded, FlacSubframeHeader& subframe, InputBitStream& bit_input)
|
|
{
|
|
u8 residual_mode = static_cast<u8>(bit_input.read_bits_big_endian(2));
|
|
u8 partition_order = static_cast<u8>(bit_input.read_bits_big_endian(4));
|
|
size_t partitions = 1 << partition_order;
|
|
|
|
if (residual_mode == FlacResidualMode::Rice4Bit) {
|
|
// decode a single Rice partition with four bits for the order k
|
|
for (size_t i = 0; i < partitions; ++i) {
|
|
auto rice_partition = decode_rice_partition(4, partitions, i, subframe, bit_input);
|
|
decoded.extend(move(rice_partition));
|
|
}
|
|
} else if (residual_mode == FlacResidualMode::Rice5Bit) {
|
|
// five bits equivalent
|
|
for (size_t i = 0; i < partitions; ++i) {
|
|
auto rice_partition = decode_rice_partition(5, partitions, i, subframe, bit_input);
|
|
decoded.extend(move(rice_partition));
|
|
}
|
|
} else {
|
|
m_error_string = "Reserved residual coding method";
|
|
return {};
|
|
}
|
|
|
|
return decoded;
|
|
}
|
|
|
|
// Decode a single Rice partition as part of the residual, every partition can have its own Rice parameter k
|
|
ALWAYS_INLINE Vector<i32> FlacLoaderPlugin::decode_rice_partition(u8 partition_type, u32 partitions, u32 partition_index, FlacSubframeHeader& subframe, InputBitStream& bit_input)
|
|
{
|
|
// Rice parameter / Exp-Golomb order
|
|
u8 k = static_cast<u8>(bit_input.read_bits_big_endian(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<i32> rice_partition;
|
|
rice_partition.resize(residual_sample_count);
|
|
|
|
// escape code for unencoded binary partition
|
|
if (k == (1 << partition_type) - 1) {
|
|
u8 unencoded_bps = static_cast<u8>(bit_input.read_bits_big_endian(5));
|
|
for (size_t r = 0; r < residual_sample_count; ++r) {
|
|
rice_partition[r] = static_cast<u8>(bit_input.read_bits_big_endian(unencoded_bps));
|
|
}
|
|
} else {
|
|
for (size_t r = 0; r < residual_sample_count; ++r) {
|
|
rice_partition[r] = 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 i32 decode_unsigned_exp_golomb(u8 k, InputBitStream& bit_input)
|
|
{
|
|
u8 q = 0;
|
|
while (bit_input.read_bit_big_endian() == 0)
|
|
++q;
|
|
|
|
// least significant bits (remainder)
|
|
u32 rem = static_cast<u32>(bit_input.read_bits_big_endian(k));
|
|
u32 value = q << k | rem;
|
|
|
|
return rice_to_signed(value);
|
|
}
|
|
|
|
u64 read_utf8_char(InputStream& input)
|
|
{
|
|
u64 character;
|
|
u8 buffer = 0;
|
|
Bytes buffer_bytes { &buffer, 1 };
|
|
input.read(buffer_bytes);
|
|
u8 start_byte = buffer_bytes[0];
|
|
// Signal byte is zero: ASCII character
|
|
if ((start_byte & 0b10000000) == 0) {
|
|
return start_byte;
|
|
} else if ((start_byte & 0b11000000) == 0b10000000) {
|
|
// illegal continuation byte
|
|
return 0;
|
|
}
|
|
// 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) {
|
|
input.read(buffer_bytes);
|
|
u8 current_byte = buffer_bytes[0];
|
|
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));
|
|
}
|
|
}
|