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95 lines
2.7 KiB
C++
95 lines
2.7 KiB
C++
#pragma once
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#include <cstdint>
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#include <mutex>
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#include <vector>
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#include <QIODevice>
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/*!
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* \brief An intermediate recepticle for audio data.
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*
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* Provides a QIODevice that will attempt to buffer the minimum amount
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* of data before handing it off to a polling QAudioOutput.
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*
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* Adding an extra buffer increases worst-case latency but resolves two
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* issues uncovered with use of a QAudioOutput by push:
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*
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* 1. knowing how much data is currently buffered, to avoid being at a
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* permanent disadvantage after startup; and
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* 2. that such QAudioOutputs empirically seem to introduce a minimum
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* 16384-byte latency.
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*/
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struct AudioBuffer: public QIODevice {
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AudioBuffer() {
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open(QIODevice::ReadOnly | QIODevice::Unbuffered);
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}
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void setDepth(size_t depth) {
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std::lock_guard lock(mutex);
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buffer.resize(depth);
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}
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// AudioBuffer-specific behaviour: always provide the latest data,
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// even if that means skipping some.
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qint64 readData(char *data, const qint64 maxlen) override {
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if(!maxlen) {
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return 0;
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}
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std::lock_guard lock(mutex);
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if(readPointer == writePointer || buffer.empty()) return 0;
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const size_t dataAvailable = std::min(writePointer - readPointer, size_t(maxlen));
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size_t bytesToCopy = dataAvailable;
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while(bytesToCopy) {
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const size_t nextLength = std::min(buffer.size() - (readPointer % buffer.size()), bytesToCopy);
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memcpy(data, &buffer[readPointer % buffer.size()], nextLength);
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bytesToCopy -= nextLength;
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data += nextLength;
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readPointer += nextLength;
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}
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return qint64(dataAvailable);
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}
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qint64 bytesAvailable() const override {
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std::lock_guard lock(mutex);
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return qint64(writePointer - readPointer);
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}
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// Required to make QIODevice concrete; not used.
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qint64 writeData(const char *, qint64) override {
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return 0;
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}
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// Posts a new set of source data. This buffer permits only the amount of data
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// specified by @c setDepth to be enqueued into the future. Additional writes
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// after the buffer is full will overwrite the newest data.
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void write(const std::vector<int16_t> &source) {
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std::lock_guard lock(mutex);
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if(buffer.empty()) return;
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const size_t sourceSize = source.size() * sizeof(int16_t);
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size_t bytesToCopy = sourceSize;
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auto data = reinterpret_cast<const uint8_t *>(source.data());
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while(bytesToCopy) {
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size_t nextLength = std::min(buffer.size() - (writePointer % buffer.size()), bytesToCopy);
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memcpy(&buffer[writePointer % buffer.size()], data, nextLength);
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bytesToCopy -= nextLength;
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data += nextLength;
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writePointer += nextLength;
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}
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readPointer = std::max(readPointer, writePointer - buffer.size());
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}
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private:
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mutable std::mutex mutex;
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std::vector<uint8_t> buffer;
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mutable size_t readPointer = 0;
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size_t writePointer = 0;
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};
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