fixedjitterbuf.c

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/*
 * Copyright (C) 2005, Attractel OOD
 *
 * Contributors:
 * Slav Klenov <slav@securax.org>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 *
 * A license has been granted to Digium (via disclaimer) for the use of
 * this code.
 */
 
/*! \file
 *
 * \brief Jitterbuffering algorithm.
 *
 * \author Slav Klenov <slav@securax.org>
 */
 
/*** MODULEINFO
    <support_level>core</support_level>
 ***/
 
#include "asterisk.h"
 
#include <assert.h>
 
#include "asterisk/utils.h"
#include "fixedjitterbuf.h"
 
#undef FIXED_JB_DEBUG
 
#ifdef FIXED_JB_DEBUG
#define ASSERT(a)
#else
#define ASSERT(a) ast_assert(a)
#endif
 
/*! \brief private fixed_jb structure */
struct fixed_jb
{
    struct fixed_jb_frame *frames;
    struct fixed_jb_frame *tail;
    struct fixed_jb_conf conf;
    long rxcore;
    long delay;
    long next_delivery;
    int force_resynch;
};
 
 
static struct fixed_jb_frame *alloc_jb_frame(struct fixed_jb *jb);
static void release_jb_frame(struct fixed_jb *jb, struct fixed_jb_frame *frame);
static void get_jb_head(struct fixed_jb *jb, struct fixed_jb_frame *frame);
static int resynch_jb(struct fixed_jb *jb, void *data, long ms, long ts, long now);
 
static inline struct fixed_jb_frame *alloc_jb_frame(struct fixed_jb *jb)
{
    return ast_calloc(1, sizeof(*jb));
}
 
static inline void release_jb_frame(struct fixed_jb *jb, struct fixed_jb_frame *frame)
{
    ast_free(frame);
}
 
static void get_jb_head(struct fixed_jb *jb, struct fixed_jb_frame *frame)
{
    struct fixed_jb_frame *fr;
 
    /* unlink the frame */
    fr = jb->frames;
    jb->frames = fr->next;
    if (jb->frames) {
        jb->frames->prev = NULL;
    } else {
        /* the jb is empty - update tail */
        jb->tail = NULL;
    }
 
    /* update next */
    jb->next_delivery = fr->delivery + fr->ms;
 
    /* copy the destination */
    memcpy(frame, fr, sizeof(struct fixed_jb_frame));
 
    /* and release the frame */
    release_jb_frame(jb, fr);
}
 
 
struct fixed_jb *fixed_jb_new(struct fixed_jb_conf *conf)
{
    struct fixed_jb *jb;
 
    if (!(jb = ast_calloc(1, sizeof(*jb))))
        return NULL;
 
    /* First copy our config */
    memcpy(&jb->conf, conf, sizeof(struct fixed_jb_conf));
 
    /* we don't need the passed config anymore - continue working with the saved one */
    conf = &jb->conf;
 
    /* validate the configuration */
    if (conf->jbsize < 1)
        conf->jbsize = FIXED_JB_SIZE_DEFAULT;
 
    if (conf->resync_threshold < 1)
        conf->resync_threshold = FIXED_JB_RESYNCH_THRESHOLD_DEFAULT;
 
    /* Set the constant delay to the jitterbuf */
    jb->delay = conf->jbsize;
 
    return jb;
}
 
 
void fixed_jb_destroy(struct fixed_jb *jb)
{
    /* jitterbuf MUST be empty before it can be destroyed */
    ASSERT(jb->frames == NULL);
 
    ast_free(jb);
}
 
 
static int resynch_jb(struct fixed_jb *jb, void *data, long ms, long ts, long now)
{
    long diff, offset;
    struct fixed_jb_frame *frame;
 
    /* If jb is empty, just reinitialize the jb */
    if (!jb->frames) {
        /* debug check: tail should also be NULL */
        ASSERT(jb->tail == NULL);
 
        return fixed_jb_put_first(jb, data, ms, ts, now);
    }
 
    /* Adjust all jb state just as the new frame is with delivery = the delivery of the last
       frame (e.g. this one with max delivery) + the length of the last frame. */
 
    /* Get the diff in timestamps */
    diff = ts - jb->tail->ts;
 
    /* Ideally this should be just the length of the last frame. The deviation is the desired
       offset */
    offset = diff - jb->tail->ms;
 
    /* Do we really need to resynch, or this is just a frame for dropping? */
    if (!jb->force_resynch && (offset < jb->conf.resync_threshold && offset > -jb->conf.resync_threshold))
        return FIXED_JB_DROP;
 
    /* Reset the force resynch flag */
    jb->force_resynch = 0;
 
    /* apply the offset to the jb state */
    jb->rxcore -= offset;
    frame = jb->frames;
    while (frame) {
        frame->ts += offset;
        frame = frame->next;
    }
 
    /* now jb_put() should add the frame at a last position */
    return fixed_jb_put(jb, data, ms, ts, now);
}
 
 
void fixed_jb_set_force_resynch(struct fixed_jb *jb)
{
    jb->force_resynch = 1;
}
 
 
int fixed_jb_put_first(struct fixed_jb *jb, void *data, long ms, long ts, long now)
{
    /* this is our first frame - set the base of the receivers time */
    jb->rxcore = now - ts;
 
    /* init next for a first time - it should be the time the first frame should be played */
    jb->next_delivery = now + jb->delay;
 
    /* put the frame */
    return fixed_jb_put(jb, data, ms, ts, now);
}
 
int fixed_jb_put(struct fixed_jb *jb, void *data, long ms, long ts, long now)
{
    struct fixed_jb_frame *frame, *next, *newframe;
    long delivery;
 
    /* debug check the validity of the input params */
    ASSERT(data != NULL);
    /* do not allow frames shorter than 2 ms */
    ASSERT(ms >= 2);
    ASSERT(ts >= 0);
    ASSERT(now >= 0);
 
    delivery = jb->rxcore + jb->delay + ts;
 
    /* check if the new frame is not too late */
    if (delivery < jb->next_delivery) {
        /* should drop the frame, but let first resynch_jb() check if this is not a jump in ts, or
           the force resynch flag was not set. */
        return resynch_jb(jb, data, ms, ts, now);
    }
 
    /* what if the delivery time is bigger than next + delay? Seems like a frame for the future.
       However, allow more resync_threshold ms in advance */
    if (delivery > jb->next_delivery + jb->delay + jb->conf.resync_threshold) {
        /* should drop the frame, but let first resynch_jb() check if this is not a jump in ts, or
           the force resynch flag was not set. */
        return resynch_jb(jb, data, ms, ts, now);
    }
 
    /* find the right place in the frames list, sorted by delivery time */
    frame = jb->tail;
    while (frame && frame->delivery > delivery) {
        frame = frame->prev;
    }
 
    /* Check if the new delivery time is not covered already by the chosen frame */
    if (frame && (frame->delivery == delivery ||
                 delivery < frame->delivery + frame->ms ||
                 (frame->next && delivery + ms > frame->next->delivery)))
    {
        /* TODO: Should we check for resynch here? Be careful to do not allow threshold smaller than
           the size of the jb */
 
        /* should drop the frame, but let first resynch_jb() check if this is not a jump in ts, or
           the force resynch flag was not set. */
        return resynch_jb(jb, data, ms, ts, now);
    }
 
    /* Reset the force resynch flag */
    jb->force_resynch = 0;
 
    /* Get a new frame */
    newframe = alloc_jb_frame(jb);
    newframe->data = data;
    newframe->ts = ts;
    newframe->ms = ms;
    newframe->delivery = delivery;
 
    /* and insert it right on place */
    if (frame) {
        next = frame->next;
        frame->next = newframe;
        if (next) {
            newframe->next = next;
            next->prev = newframe;
        } else {
            /* insert after the last frame - should update tail */
            jb->tail = newframe;
            newframe->next = NULL;
        }
        newframe->prev = frame;
 
        return FIXED_JB_OK;
    } else if (!jb->frames) {
        /* the frame list is empty or thats just the first frame ever */
        /* tail should also be NULL is that case */
        ASSERT(jb->tail == NULL);
        jb->frames = jb->tail = newframe;
        newframe->next = NULL;
        newframe->prev = NULL;
 
        return FIXED_JB_OK;
    } else {
        /* insert on a first position - should update frames head */
        newframe->next = jb->frames;
        newframe->prev = NULL;
        jb->frames->prev = newframe;
        jb->frames = newframe;
 
        return FIXED_JB_OK;
    }
}
 
 
int fixed_jb_get(struct fixed_jb *jb, struct fixed_jb_frame *frame, long now, long interpl)
{
    ASSERT(now >= 0);
    ASSERT(interpl >= 2);
 
    if (now < jb->next_delivery) {
        /* too early for the next frame */
        return FIXED_JB_NOFRAME;
    }
 
    /* Is the jb empty? */
    if (!jb->frames) {
        /* should interpolate a frame */
        /* update next */
        jb->next_delivery += interpl;
 
        return FIXED_JB_INTERP;
    }
 
    /* Isn't it too late for the first frame available in the jb? */
    if (now > jb->frames->delivery + jb->frames->ms) {
        /* yes - should drop this frame and update next to point the next frame (get_jb_head() does it) */
        get_jb_head(jb, frame);
 
        return FIXED_JB_DROP;
    }
 
    /* isn't it too early to play the first frame available? */
    if (now < jb->frames->delivery) {
        /* yes - should interpolate one frame */
        /* update next */
        jb->next_delivery += interpl;
 
        return FIXED_JB_INTERP;
    }
 
    /* we have a frame for playing now (get_jb_head() updates next) */
    get_jb_head(jb, frame);
 
    return FIXED_JB_OK;
}
 
 
long fixed_jb_next(struct fixed_jb *jb)
{
    return jb->next_delivery;
}
 
 
int fixed_jb_remove(struct fixed_jb *jb, struct fixed_jb_frame *frameout)
{
    if (!jb->frames)
        return FIXED_JB_NOFRAME;
 
    get_jb_head(jb, frameout);
 
    return FIXED_JB_OK;
}
 
int fixed_jb_is_late(struct fixed_jb *jb, long ts)
{
    return jb->rxcore + jb->delay + ts < jb->next_delivery;
}