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/*
* Copyright 2023 jacqueline <me@jacqueline.id.au>
*
* SPDX-License-Identifier: GPL-3.0-only
*/
#include "mad.hpp"
#include <stdint.h>
#include <cstdint>
#include <optional>
#include "mad.h"
#include "codec.hpp"
#include "result.hpp"
#include "types.hpp"
namespace codecs {
static uint32_t mad_fixed_to_pcm(mad_fixed_t sample, uint8_t bits) {
// Round the bottom bits.
sample += (1L << (MAD_F_FRACBITS - bits));
// Clip the leftover bits to within range.
if (sample >= MAD_F_ONE)
sample = MAD_F_ONE - 1;
else if (sample < -MAD_F_ONE)
sample = -MAD_F_ONE;
// Quantize.
return sample >> (MAD_F_FRACBITS + 1 - bits);
}
MadMp3Decoder::MadMp3Decoder() {
mad_stream_init(&stream_);
mad_frame_init(&frame_);
mad_synth_init(&synth_);
}
MadMp3Decoder::~MadMp3Decoder() {
mad_stream_finish(&stream_);
mad_frame_finish(&frame_);
mad_synth_finish(&synth_);
}
auto MadMp3Decoder::GetInputPosition() -> std::size_t {
assert(stream_.next_frame >= stream_.buffer);
return stream_.next_frame - stream_.buffer;
}
auto MadMp3Decoder::BeginStream(const cpp::span<const std::byte> input)
-> Result<OutputFormat> {
mad_stream_buffer(&stream_,
reinterpret_cast<const unsigned char*>(input.data()),
input.size_bytes());
// Whatever was last synthesized is now invalid, so ensure we don't try to
// send it.
current_sample_ = -1;
// To get the output format for MP3 streams, we simply need to decode the
// first frame header.
mad_header header;
mad_header_init(&header);
while (mad_header_decode(&header, &stream_) < 0) {
if (MAD_RECOVERABLE(stream_.error)) {
// Recoverable errors are usually malformed parts of the stream.
// We can recover from them by just retrying the decode.
continue;
}
if (stream_.error == MAD_ERROR_BUFLEN) {
return {GetInputPosition(), cpp::fail(Error::kOutOfInput)};
}
return {GetInputPosition(), cpp::fail(Error::kMalformedData)};
}
uint8_t channels = MAD_NCHANNELS(&header);
return {GetInputPosition(),
OutputFormat{
.num_channels = channels,
.bits_per_sample = 24, // We always scale to 24 bits
.sample_rate_hz = header.samplerate,
}};
}
auto MadMp3Decoder::ContinueStream(cpp::span<const std::byte> input,
cpp::span<std::byte> output)
-> Result<OutputInfo> {
if (current_sample_ < 0) {
mad_stream_buffer(&stream_,
reinterpret_cast<const unsigned char*>(input.data()),
input.size());
// Decode the next frame. To signal errors, this returns -1 and
// stashes an error code in the stream structure.
while (mad_frame_decode(&frame_, &stream_) < 0) {
if (MAD_RECOVERABLE(stream_.error)) {
// Recoverable errors are usually malformed parts of the stream.
// We can recover from them by just retrying the decode.
continue;
}
if (stream_.error == MAD_ERROR_BUFLEN) {
// The decoder ran out of bytes before it completed a frame. We
// need to return back to the caller to give us more data.
return {GetInputPosition(), cpp::fail(Error::kOutOfInput)};
}
// The error is unrecoverable. Give up.
return {GetInputPosition(), cpp::fail(Error::kMalformedData)};
}
// We've successfully decoded a frame! Now synthesize samples to write out.
mad_synth_frame(&synth_, &frame_);
current_sample_ = 0;
}
size_t output_byte = 0;
while (current_sample_ < synth_.pcm.length) {
if (output_byte + (4 * synth_.pcm.channels) >= output.size()) {
// We can't fit the next sample into the buffer. Stop now, and also avoid
// writing the sample for only half the channels.
return {GetInputPosition(), OutputInfo{.bytes_written = output_byte,
.is_finished_writing = false}};
}
for (int channel = 0; channel < synth_.pcm.channels; channel++) {
uint32_t sample_24 =
mad_fixed_to_pcm(synth_.pcm.samples[channel][current_sample_], 24);
output[output_byte++] = static_cast<std::byte>((sample_24 >> 16) & 0xFF);
output[output_byte++] = static_cast<std::byte>((sample_24 >> 8) & 0xFF);
output[output_byte++] = static_cast<std::byte>((sample_24)&0xFF);
// 24 bit samples must still be aligned to 32 bits. The LSB is ignored.
output[output_byte++] = static_cast<std::byte>(0);
}
current_sample_++;
}
// We wrote everything! Reset, ready for the next frame.
current_sample_ = -1;
return {GetInputPosition(), OutputInfo{.bytes_written = output_byte,
.is_finished_writing = true}};
}
auto MadMp3Decoder::SeekStream(cpp::span<const std::byte> input,
std::size_t target_sample) -> Result<void> {
mad_stream_buffer(&stream_,
reinterpret_cast<const unsigned char*>(input.data()),
input.size());
std::size_t current_sample = 0;
std::size_t samples_per_frame = 0;
while (true) {
current_sample += samples_per_frame;
// First, decode the header for this frame.
mad_header header;
mad_header_init(&header);
while (mad_header_decode(&header, &stream_) < 0) {
if (MAD_RECOVERABLE(stream_.error)) {
// Recoverable errors are usually malformed parts of the stream.
// We can recover from them by just retrying the decode.
continue;
} else {
// Don't bother checking for other errors; if the first part of the
// stream doesn't even contain a header then something's gone wrong.
return {GetInputPosition(), cpp::fail(Error::kMalformedData)};
}
}
// Calculate samples per frame if we haven't already.
if (samples_per_frame == 0) {
samples_per_frame = 32 * MAD_NSBSAMPLES(&header);
}
// Work out how close we are to the target.
std::size_t samples_to_go = target_sample - current_sample;
std::size_t frames_to_go = samples_to_go / samples_per_frame;
if (frames_to_go > 3) {
// The target is far in the distance. Keep skipping through headers only.
continue;
}
// The target is within the next few frames. We should decode these, to give
// the decoder a chance to sync with the stream.
while (mad_frame_decode(&frame_, &stream_) < 0) {
if (MAD_RECOVERABLE(stream_.error)) {
continue;
}
if (stream_.error == MAD_ERROR_BUFLEN) {
return {GetInputPosition(), cpp::fail(Error::kOutOfInput)};
}
// The error is unrecoverable. Give up.
return {GetInputPosition(), cpp::fail(Error::kMalformedData)};
}
if (frames_to_go <= 1) {
// The target is within the next couple of frames. We should start
// synthesizing a frame early because this guy says so:
// https://lists.mars.org/hyperkitty/list/mad-dev@lists.mars.org/message/UZSHXZTIZEF7FZ4KFOR65DUCKAY2OCUT/
mad_synth_frame(&synth_, &frame_);
}
if (frames_to_go == 0) {
// The target is actually within this frame! Set up for the ContinueStream
// call.
current_sample_ =
(target_sample > current_sample) ? target_sample - current_sample : 0;
return {GetInputPosition(), {}};
}
}
}
} // namespace codecs
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