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Modified audio handling to use SDL_QueueAudio to simplify code and changed remaining bytes calculation to reduce audio latency

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This commit is contained in:
Mr-Wiseguy 2023-02-15 23:41:14 -05:00
parent 7babd24bd1
commit 38f6304d44
1 changed files with 33 additions and 87 deletions
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120
test/portultra/audio.cpp
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@ -5,6 +5,7 @@
#include <cassert>
static SDL_AudioDeviceID audio_device = 0;
static uint32_t sample_rate = 48000;
void Multilibultra::init_audio() {
// Initialize SDL audio.
@ -13,8 +14,6 @@ void Multilibultra::init_audio() {
set_audio_frequency(48000);
}
void SDLCALL feed_audio(void* userdata, Uint8* stream, int len);
void Multilibultra::set_audio_frequency(uint32_t freq) {
if (audio_device != 0) {
SDL_CloseAudioDevice(audio_device);
@ -27,7 +26,7 @@ void Multilibultra::set_audio_frequency(uint32_t freq) {
.samples = 0x100, // Fairly small sample count to reduce the latency of internal buffering
.padding = 0, // unused
.size = 0, // calculated
.callback = feed_audio, // Use a callback as QueueAudio causes popping
.callback = nullptr,//feed_audio, // Use a callback as QueueAudio causes popping
.userdata = nullptr
};
@ -38,105 +37,52 @@ void Multilibultra::set_audio_frequency(uint32_t freq) {
assert(false);
}
SDL_PauseAudioDevice(audio_device, 0);
}
// Struct representing a queued audio buffer.
struct AudioBuffer {
// All samples in the buffer, including those that have already been sent.
std::vector<int16_t> samples;
// The count of samples that have already been sent to the audio device.
size_t used_samples = 0;
// Helper methods.
size_t remaining_samples() const { return samples.size() - used_samples; };
size_t remaining_bytes() const { return remaining_samples() * sizeof(samples[0]); };
int16_t* first_unused_sample() { return &samples[used_samples]; }
bool empty() { return used_samples == samples.size(); }
};
// Mutex for locking the queued audio buffer list.
std::mutex audio_buffers_mutex;
// The queued audio buffer list, holds a list of buffers that have been queued by the game.
std::vector<AudioBuffer> audio_buffers;
void SDLCALL feed_audio(void* userdata, Uint8* stream, int byte_count) {
// Ensure that the byte count is an integer multiple of samples.
assert((byte_count & 1) == 0);
// Calculate the sample count from the byte count.
size_t remaining_samples = byte_count / sizeof(int16_t);
// Lock the queued audio buffer list.
std::lock_guard lock{ audio_buffers_mutex };
// Empty the audio buffers until we've sent all the required samples
// or until there are no samples left in the audio buffers.
while (!audio_buffers.empty() && remaining_samples > 0) {
auto& cur_buffer = audio_buffers.front();
// Prevent overrunning either the input or output buffer.
size_t to_copy = std::min(remaining_samples, cur_buffer.remaining_samples());
// Copy samples from the input buffer to the output one.
memcpy(stream, cur_buffer.first_unused_sample(), to_copy * sizeof(int16_t));
// Advance the output buffer by the copied byte count.
stream += to_copy * sizeof(int16_t);
// Advance the input buffer by the copied sample count.
cur_buffer.used_samples += to_copy;
// Updated the remaining sample count.
remaining_samples -= to_copy;
// If the input buffer was emptied, remove it from the list of queued buffers.
if (cur_buffer.empty()) {
audio_buffers.erase(audio_buffers.begin());
}
}
// Zero out any remaining audio data to lessen audio issues during lag
memset(stream, 0, remaining_samples * sizeof(int16_t));
sample_rate = freq;
}
void Multilibultra::queue_audio_buffer(RDRAM_ARG PTR(s16) audio_data_, uint32_t byte_count) {
// Buffer for holding the output of swapping the audio channels. This is reused across
// calls to reduce runtime allocations.
static std::vector<uint16_t> swap_buffer;
// Ensure that the byte count is an integer multiple of samples.
assert((byte_count & 1) == 0);
s16* audio_data = TO_PTR(s16, audio_data_);
// Calculate the number of samples from the number of bytes.
uint32_t sample_count = byte_count / sizeof(s16);
// Lock the queued audio buffer list.
std::lock_guard lock{ audio_buffers_mutex };
// Set up a new queued audio buffer.
AudioBuffer& new_buf = audio_buffers.emplace_back();
new_buf.samples.resize(sample_count);
new_buf.used_samples = 0;
// Copy the data into the new buffer.
// Swap the audio channels to correct for the address xor caused by endianness handling.
for (size_t i = 0; i < sample_count; i += 2) {
new_buf.samples[i + 0] = audio_data[i + 1];
new_buf.samples[i + 1] = audio_data[i + 0];
// Make sure the swap buffer is large enough to hold all the incoming audio data.
if (sample_count > swap_buffer.size()) {
swap_buffer.resize(sample_count);
}
// Swap the audio channels into the swap buffer to correct for the address xor caused by endianness handling.
s16* audio_data = TO_PTR(s16, audio_data_);
for (size_t i = 0; i < sample_count; i += 2) {
swap_buffer[i + 0] = audio_data[i + 1];
swap_buffer[i + 1] = audio_data[i + 0];
}
// Queue the swapped audio data.
SDL_QueueAudio(audio_device, swap_buffer.data(), byte_count);
}
// If there's ever any audio popping, check here first. Some games are very sensitive to
// the remaining sample count and reporting a number that's too high here can lead to issues.
// Reporting a number that's too low can lead to audio lag in some games.
uint32_t Multilibultra::get_remaining_audio_bytes() {
// Calculate the number of samples still in the queued audio buffers
size_t buffered_byte_count = 0;
{
// Lock the queued audio buffer list.
std::lock_guard lock{ audio_buffers_mutex };
// Gather the remaining byte count of the next buffer, if any exists.
if (!audio_buffers.empty()) {
buffered_byte_count = audio_buffers.front().remaining_bytes();
}
}
// Add the number of remaining bytes in the audio data that's been sent to the device.
buffered_byte_count += SDL_GetQueuedAudioSize(audio_device);
// Get the number of remaining buffered audio bytes.
uint32_t buffered_byte_count = SDL_GetQueuedAudioSize(audio_device);
// Add a slight positive scaling bias, which helps audio respond quicker. Remove the bias
// if games have popping issues.
return buffered_byte_count + (buffered_byte_count / 10);
// Adjust the reported count to be four refreshes in the future, which helps ensure that
// there are enough samples even if the game experiences a small amount of lag. This prevents
// audio popping on games that use the buffered audio byte count to determine how many samples
// to generate.
uint32_t samples_per_vi = (sample_rate / 60);
if (buffered_byte_count > (4u * samples_per_vi)) {
buffered_byte_count -= (4u * samples_per_vi);
} else {
buffered_byte_count = 0;
}
return buffered_byte_count;
}