audio_buffer.c

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/*
 * Copyright (c) 2016-2021 CESNET, z. s. p. o.
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 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
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 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS
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#ifdef HAVE_CONFIG_H
#include "config.h"
#include "config_unix.h"
#include "config_win32.h"
#endif
 
#include "audio/types.h"
#include "debug.h"
#include "host.h"
#include "utils/audio_buffer.h"
#include "utils/ring_buffer.h"
 
#define WINDOW 50
 
#undef max
#undef min
#define max(a, b)      (((a) > (b))? (a): (b))
#define min(a, b)      (((a) < (b))? (a): (b))
 
#define BUF_LAST_UNDERRUN_MAX 1000000000
#define BUF_LAST_UNDERRUN_THRESHOLD 10000
#define BUF_LAST_OVERRUN_THRESHOLD 10000
#define AGGRESSIVITY_MAX 4
#define AGGRESSIVITY_STEP 100
 
static const int occupacy_windows[] = { 50, 200 };
 
struct audio_buffer {
        struct audio_desc desc;
        ring_buffer_t *ring;
        int suggested_latency_ms;
 
        // moving averages
        int in_pkt_size;
        int out_pkt_size;
        int avg_occupancy[2]; // at read time
        int last_underrun; // last underrun n output frames ago
        int last_overrun; // last overrun n output frames ago
        int aggressivity;
        int last_aggressivity_change;
};
 
struct audio_buffer *audio_buffer_init(int sample_rate, int bps, int ch_count, int suggested_latency_ms)
{
        struct audio_buffer *buf = calloc(1, sizeof(struct audio_buffer));
        buf->desc.sample_rate = sample_rate;
        buf->desc.bps = bps;
        buf->desc.ch_count = ch_count;
 
        buf->last_underrun = BUF_LAST_UNDERRUN_MAX;
 
        buf->ring = ring_buffer_init(sample_rate * bps * ch_count);
 
        buf->suggested_latency_ms = suggested_latency_ms;
 
        buf->aggressivity = 1;
        buf->last_aggressivity_change = AGGRESSIVITY_STEP;
 
        return buf;
}
 
void audio_buffer_destroy(struct audio_buffer *buf)
{
        if (!buf) {
                return;
        }
        ring_buffer_destroy(buf->ring);
        free(buf);
}
 
int audio_buffer_read(struct audio_buffer *buf, char *out, int max_len)
{
        if (buf->out_pkt_size > 0) {
                buf->out_pkt_size = (max_len + (buf->out_pkt_size * (WINDOW-1))) / WINDOW;
        } else {
                buf->out_pkt_size = max_len;
        }
 
        int ring_size = ring_get_current_size(buf->ring);
 
        for (unsigned int i = 0; i < sizeof buf->avg_occupancy / sizeof buf->avg_occupancy[0]; ++i) {
                if (buf->avg_occupancy[i] > 0) {
                        buf->avg_occupancy[i] = (ring_size + (buf->avg_occupancy[i] * (occupacy_windows[i] -1))) / occupacy_windows[i];
                } else {
                        buf->avg_occupancy[i] = ring_size;
                }
        }
 
        // handle underruns
        if (ring_size < max_len) {
                buf->last_underrun = 0;
        } else {
                if (buf->last_underrun < BUF_LAST_UNDERRUN_MAX) {
                        buf->last_underrun += 1;
                }
        }
 
        int suggested_latency_bytes = buf->suggested_latency_ms * buf->desc.bps * buf->desc.ch_count * buf->desc.sample_rate / 1000;
        int requested_latency_bytes = max(suggested_latency_bytes, 2*max(buf->in_pkt_size, buf->out_pkt_size));
 
        int ret = ring_buffer_read(buf->ring, out, max_len);
 
        // fiddle aggressivity
        if (buf->last_aggressivity_change >= AGGRESSIVITY_STEP) {
                buf->last_aggressivity_change = 0;
                if ((buf->avg_occupancy[0] > buf->avg_occupancy[1] && buf->last_underrun > BUF_LAST_UNDERRUN_THRESHOLD / 10) && buf->last_overrun <= BUF_LAST_OVERRUN_THRESHOLD) {
                        buf->aggressivity = min(buf->aggressivity + 1, AGGRESSIVITY_MAX);
                } else if (buf->avg_occupancy[0] < buf->avg_occupancy[1] || buf->last_underrun < BUF_LAST_UNDERRUN_THRESHOLD / 100 || buf->last_overrun > BUF_LAST_OVERRUN_THRESHOLD) {
                        buf->aggressivity = max(buf->aggressivity - 1, 1);
                }
        } else {
                buf->last_aggressivity_change += 1;
        }
 
        // handle overruns
        int remaining_bytes = ring_size - ret;
        if (requested_latency_bytes < remaining_bytes) {
                int len_drop = (1<<buf->aggressivity) * buf->desc.bps * buf->desc.ch_count * 128;
                len_drop = min(len_drop, remaining_bytes / 2);
 
                char *tmp = alloca(len_drop);
                ring_buffer_read(buf->ring, tmp, len_drop);
                buf->last_overrun = 0;
                log_msg(LOG_LEVEL_VERBOSE, "Dropped audio samples: req latency %d remaining %d dropped %d!\n", requested_latency_bytes, remaining_bytes, len_drop);
        } else {
                buf->last_overrun += 1;
        }
 
        log_msg(LOG_LEVEL_DEBUG, "buf - in a. %d, out a. %d, occ. a. [%d,%d] last under/overrun %d, %d aggressivity %d\n", buf->in_pkt_size, buf->out_pkt_size, buf->avg_occupancy[0],buf->avg_occupancy[1], buf->last_underrun, buf->last_overrun, buf->aggressivity);
 
        return ret;
}
 
void audio_buffer_write(struct audio_buffer *buf, const char *in, int len)
{
        if (buf->in_pkt_size > 0) {
                buf->in_pkt_size = (len + (buf->in_pkt_size * (WINDOW-1))) / WINDOW;
        } else {
                buf->in_pkt_size = len;
        }
        ring_buffer_write(buf->ring, in, len);
}
 
struct audio_buffer_api audio_buffer_fns = {
        (void (*)(void *)) audio_buffer_destroy,
        (int (*)(void *, char *, int)) audio_buffer_read,
        (void (*)(void *, const char *, int)) audio_buffer_write,
};