pipewire/spa/plugins/bluez5/decode-buffer.h

/* Spa Bluez5 decode buffer */
/* SPDX-FileCopyrightText: Copyright © 2022 Pauli Virtanen */
/* SPDX-License-Identifier: MIT */

/**
 * \file decode-buffer.h   Buffering for Bluetooth sources
 *
 * A linear buffer, which is compacted when it gets half full.
 *
 * Also contains buffering logic, which calculates a rate correction
 * factor to maintain the buffer level at the target value.
 *
 * Consider typical packet intervals with nominal frame duration
 * of 10ms:
 *
 *     ... 5ms | 5ms | 20ms | 5ms | 5ms | 20ms ...
 *
 *     ... 3ms | 3ms | 4ms | 30ms | 3ms | 3ms | 4ms | 30ms ...
 *
 * plus random jitter; 10ms nominal may occasionally have 20+ms interval.
 * The regular timer cycle cannot be aligned with this, so process()
 * may occur at any time.
 *
 * The buffer level is the position of last received sample, relative to the current
 * playback position. If it is larger than duration, there is no underrun.
 *
 * The rate correction aims to maintain the average level at a safety margin.
 */

#ifndef SPA_BLUEZ5_DECODE_BUFFER_H
#define SPA_BLUEZ5_DECODE_BUFFER_H

#include <stdlib.h>
#include <spa/utils/defs.h>
#include <spa/support/log.h>

#include "rate-control.h"

#define BUFFERING_LONG_MSEC		(2*60000)
#define BUFFERING_SHORT_MSEC		1000
#define BUFFERING_RATE_DIFF_MAX		0.005


struct spa_bt_decode_buffer
{
	struct spa_log *log;

	uint32_t frame_size;
	uint32_t rate;

	uint8_t *buffer_decoded;
	uint32_t buffer_size;
	uint32_t buffer_reserve;
	uint32_t write_index;
	uint32_t read_index;

	struct spa_bt_ptp spike;	/**< spikes (long window) */
	struct spa_bt_ptp packet_size;	/**< packet size (short window) */

	struct spa_bt_rate_control ctl;
	double corr;

	uint32_t duration;
	uint32_t pos;

	int32_t target;		/**< target buffer (0: automatic) */
	int32_t max_extra;

	int32_t level;
	uint64_t next_nsec;
	double rate_diff;

	uint8_t buffering:1;
};

static inline int spa_bt_decode_buffer_init(struct spa_bt_decode_buffer *this, struct spa_log *log,
		uint32_t frame_size, uint32_t rate, uint32_t quantum_limit, uint32_t reserve)
{
	spa_zero(*this);
	this->frame_size = frame_size;
	this->rate = rate;
	this->log = log;
	this->buffer_reserve = this->frame_size * reserve;
	this->buffer_size = this->frame_size * quantum_limit * 2;
	this->buffer_size += this->buffer_reserve;
	this->corr = 1.0;
	this->target = 0;
	this->buffering = true;
	this->max_extra = INT32_MAX;

	spa_bt_rate_control_init(&this->ctl, 0);

	spa_bt_ptp_init(&this->spike, (uint64_t)this->rate * BUFFERING_LONG_MSEC / 1000, 0);
	spa_bt_ptp_init(&this->packet_size, (uint64_t)this->rate * BUFFERING_SHORT_MSEC / 1000, 0);

	if ((this->buffer_decoded = malloc(this->buffer_size)) == NULL) {
		this->buffer_size = 0;
		return -ENOMEM;
	}
	return 0;
}

static inline void spa_bt_decode_buffer_clear(struct spa_bt_decode_buffer *this)
{
	free(this->buffer_decoded);
	spa_zero(*this);
}

static inline void spa_bt_decode_buffer_compact(struct spa_bt_decode_buffer *this)
{
	uint32_t avail;

	spa_assert(this->read_index <= this->write_index);

	if (this->read_index == this->write_index) {
		this->read_index = 0;
		this->write_index = 0;
		goto done;
	}

	if (this->write_index > this->read_index + this->buffer_size - this->buffer_reserve) {
		/* Drop data to keep buffer reserve free */
		spa_log_info(this->log, "%p buffer overrun: dropping data", this);
		this->read_index = this->write_index + this->buffer_reserve - this->buffer_size;
	}

	if (this->write_index < (this->buffer_size - this->buffer_reserve) / 2
			|| this->read_index == 0)
		goto done;

	avail = this->write_index - this->read_index;
	spa_memmove(this->buffer_decoded,
			SPA_PTROFF(this->buffer_decoded, this->read_index, void),
			avail);
	this->read_index = 0;
	this->write_index = avail;

done:
	spa_assert(this->buffer_size - this->write_index >= this->buffer_reserve);
}

static inline void *spa_bt_decode_buffer_get_read(struct spa_bt_decode_buffer *this, uint32_t *avail)
{
	spa_assert(this->write_index >= this->read_index);
	if (!this->buffering)
		*avail = this->write_index - this->read_index;
	else
		*avail = 0;
	return SPA_PTROFF(this->buffer_decoded, this->read_index, void);
}

static inline void spa_bt_decode_buffer_read(struct spa_bt_decode_buffer *this, uint32_t size)
{
	spa_assert(size % this->frame_size == 0);
	this->read_index += size;
}

static inline void *spa_bt_decode_buffer_get_write(struct spa_bt_decode_buffer *this, uint32_t *avail)
{
	spa_bt_decode_buffer_compact(this);
	spa_assert(this->buffer_size >= this->write_index);
	*avail = this->buffer_size - this->write_index;
	return SPA_PTROFF(this->buffer_decoded, this->write_index, void);
}

static inline void spa_bt_decode_buffer_write_packet(struct spa_bt_decode_buffer *this, uint32_t size, uint64_t nsec)
{
	int32_t remain;
	uint32_t avail;

	spa_assert(size % this->frame_size == 0);
	this->write_index += size;
	spa_bt_ptp_update(&this->packet_size, size / this->frame_size, size / this->frame_size);

	if (nsec && this->next_nsec && this->rate_diff != 0.0) {
		int64_t dt = (this->next_nsec >= nsec) ?
			(int64_t)(this->next_nsec - nsec) : -(int64_t)(nsec - this->next_nsec);
		remain = (int32_t)SPA_CLAMP(dt * this->rate_diff * this->rate / SPA_NSEC_PER_SEC,
				-(int32_t)this->duration, this->duration);
	} else {
		remain = 0;
	}

	spa_bt_decode_buffer_get_read(this, &avail);
	this->level = avail / this->frame_size + remain;
}

static inline void spa_bt_decode_buffer_recover(struct spa_bt_decode_buffer *this)
{
	int32_t size = (this->write_index - this->read_index) / this->frame_size;

	this->level = size;
	this->corr = 1.0;
	spa_bt_rate_control_init(&this->ctl, size);
}

static inline void spa_bt_decode_buffer_set_target_latency(struct spa_bt_decode_buffer *this, int32_t samples)
{
	this->target = samples;
}

static inline void spa_bt_decode_buffer_set_max_extra_latency(struct spa_bt_decode_buffer *this, int32_t samples)
{
	this->max_extra = samples;
}

static inline int32_t spa_bt_decode_buffer_get_target_latency(struct spa_bt_decode_buffer *this)
{
	const int32_t duration = this->duration;
	const int32_t packet_size = SPA_CLAMP(this->packet_size.max, 0, INT32_MAX/8);
	const int32_t max_buf = (this->buffer_size - this->buffer_reserve) / this->frame_size;
	const int32_t spike = SPA_CLAMP(this->spike.max, 0, max_buf);
	int32_t target;

	if (this->target)
		target = this->target;
	else
		target = SPA_CLAMP(SPA_ROUND_UP(SPA_MAX(spike * 3/2, duration), 
						SPA_CLAMP((int)this->rate / 50, 1, INT32_MAX)),
				duration, max_buf - 2*packet_size);

	return SPA_MIN(target, duration + SPA_CLAMP(this->max_extra, 0, INT32_MAX - duration));
}

static inline void spa_bt_decode_buffer_process(struct spa_bt_decode_buffer *this, uint32_t samples, uint32_t duration,
		double rate_diff, uint64_t next_nsec)
{
	const uint32_t data_size = samples * this->frame_size;
	const int32_t packet_size = SPA_CLAMP(this->packet_size.max, 0, INT32_MAX/8);
	const int32_t max_level = SPA_MAX(8 * packet_size, (int32_t)duration);
	const uint32_t avg_period = (uint64_t)this->rate * BUFFERING_SHORT_MSEC / 1000;
	int32_t target;
	uint32_t avail;

	this->rate_diff = rate_diff;
	this->next_nsec = next_nsec;

	if (SPA_UNLIKELY(duration != this->duration)) {
		this->duration = duration;
		spa_bt_decode_buffer_recover(this);
	}

	target = spa_bt_decode_buffer_get_target_latency(this);

	if (SPA_UNLIKELY(this->buffering)) {
		int32_t size = (this->write_index - this->read_index) / this->frame_size;

		this->corr = 1.0;

		spa_log_trace(this->log, "%p buffering size:%d", this, (int)size);

		if (size >= SPA_MAX((int)duration, target))
			this->buffering = false;
		else
			return;

		spa_bt_ptp_update(&this->spike, packet_size, duration);
		spa_bt_decode_buffer_recover(this);
	}

	spa_bt_decode_buffer_get_read(this, &avail);

	/* Track buffer level */
	this->level = SPA_MAX(this->level, -max_level);

	spa_bt_ptp_update(&this->spike, (int32_t)this->ctl.avg - this->level, duration);

	if (this->level > SPA_MAX(4 * target, 3*(int32_t)duration) &&
			avail > data_size) {
		/* Lagging too much: drop data */
		uint32_t size = SPA_MIN(avail - data_size,
				(this->level - target) * this->frame_size);

		spa_bt_decode_buffer_read(this, size);
		spa_log_trace(this->log, "%p overrun samples:%d level:%d target:%d",
				this, (int)size/this->frame_size,
				(int)this->level, (int)target);

		spa_bt_decode_buffer_recover(this);
	}

	this->pos += duration;
	if (this->pos > this->rate) {
		spa_log_debug(this->log,
				"%p avg:%d target:%d level:%d buffer:%d spike:%d corr:%f",
				this,
				(int)this->ctl.avg,
				(int)target,
				(int)this->level,
				(int)(avail / this->frame_size),
				(int)this->spike.max,
				(double)this->corr);
		this->pos = 0;
	}

	this->corr = spa_bt_rate_control_update(&this->ctl,
			this->level, target, duration, avg_period,
			BUFFERING_RATE_DIFF_MAX);

	this->level -= duration;

	spa_bt_decode_buffer_get_read(this, &avail);
	if (avail < data_size) {
		spa_log_trace(this->log, "%p underrun samples:%d", this,
				(data_size - avail) / this->frame_size);
		this->buffering = true;
		spa_bt_ptp_update(&this->spike, (int32_t)this->ctl.avg - this->level, duration);
	}
}

#endif