translate.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2006, Digium, Inc.
 *
 * Mark Spencer <markster@digium.com>
 *
 * 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.
 */

/*! \file
 *
 * \brief Translate via the use of pseudo channels
 *
 * \author Mark Spencer <markster@digium.com>
 */

/*** MODULEINFO
   <support_level>core</support_level>
 ***/

#include "asterisk.h"

#include <sys/time.h>
#include <sys/resource.h>
#include <math.h>

#include "asterisk/lock.h"
#include "asterisk/channel.h"
#include "asterisk/translate.h"
#include "asterisk/module.h"
#include "asterisk/frame.h"
#include "asterisk/sched.h"
#include "asterisk/cli.h"
#include "asterisk/term.h"
#include "asterisk/format.h"
#include "asterisk/linkedlists.h"

/*! \todo
 * TODO: sample frames for each supported input format.
 * We build this on the fly, by taking an SLIN frame and using
 * the existing converter to play with it.
 */

/*! max sample recalc */
#define MAX_RECALC 1000

/*! \brief the list of translators */
static AST_RWLIST_HEAD_STATIC(translators, ast_translator);

struct translator_path {
   struct ast_translator *step;       /*!< Next step translator */
   uint32_t table_cost;               /*!< Complete table cost to destination */
   uint8_t multistep;                 /*!< Multiple conversions required for this translation */
};

/*!
 * \brief a matrix that, for any pair of supported formats,
 * indicates the total cost of translation and the first step.
 * The full path can be reconstricted iterating on the matrix
 * until step->dstfmt == desired_format.
 *
 * Array indexes are 'src' and 'dest', in that order.
 *
 * Note: the lock in the 'translators' list is also used to protect
 * this structure.
 */
static struct translator_path **__matrix;

/*!
 * \brief table for converting index to format values.
 *
 * \note this table is protected by the table_lock.
 */
static unsigned int *__indextable;

/*! protects the __indextable for resizing */
static ast_rwlock_t tablelock;

/* index size starts at this*/
#define INIT_INDEX 32
/* index size grows by this as necessary */
#define GROW_INDEX 16

/*! the current largest index used by the __matrix and __indextable arrays*/
static int cur_max_index;
/*! the largest index that can be used in either the __indextable or __matrix before resize must occur */
static int index_size;

static void matrix_rebuild(int samples);

/*!
 * \internal
 * \brief converts codec id to index value.
 */
static int codec_to_index(unsigned int id)
{
   int x;

   ast_rwlock_rdlock(&tablelock);
   for (x = 0; x < cur_max_index; x++) {
      if (__indextable[x] == id) {
         /* format already exists in index2format table */
         ast_rwlock_unlock(&tablelock);
         return x;
      }
   }
   ast_rwlock_unlock(&tablelock);
   return -1; /* not found */
}

/*!
 * \internal
 * \brief converts codec to index value.
 */
static int codec2index(struct ast_codec *codec)
{
   return codec_to_index(codec->id);
}

/*!
 * \internal
 * \brief converts format to codec index value.
 */
static int format2index(struct ast_format *format)
{
   return codec_to_index(ast_format_get_codec_id(format));
}

/*!
 * \internal
 * \brief add a new codec to the matrix and index table structures.
 *
 * \note it is perfectly safe to call this on codecs already indexed.
 *
 * \retval 0, success
 * \retval -1, matrix and index table need to be resized
 */
static int add_codec2index(struct ast_codec *codec)
{
   if (codec2index(codec) != -1) {
      /* format is already already indexed */
      return 0;
   }

   ast_rwlock_wrlock(&tablelock);
   if (cur_max_index == (index_size)) {
      ast_rwlock_unlock(&tablelock);
      return -1; /* hit max length */
   }
   __indextable[cur_max_index] = codec->id;
   cur_max_index++;
   ast_rwlock_unlock(&tablelock);

   return 0;
}

/*!
 * \internal
 * \brief converts index value back to codec
 */
static struct ast_codec *index2codec(int index)
{
   struct ast_codec *codec;

   if (index >= cur_max_index) {
      return 0;
   }
   ast_rwlock_rdlock(&tablelock);
   codec = ast_codec_get_by_id(__indextable[index]);
   ast_rwlock_unlock(&tablelock);

   return codec;
}

/*!
 * \internal
 * \brief resize both the matrix and index table so they can represent
 * more translators
 *
 * \note _NO_ locks can be held prior to calling this function
 *
 * \retval 0, success
 * \retval -1, failure.  Old matrix and index table can still be used though
 */
static int matrix_resize(int init)
{
   struct translator_path **tmp_matrix = NULL;
   unsigned int *tmp_table = NULL;
   int old_index;
   int x;

   AST_RWLIST_WRLOCK(&translators);
   ast_rwlock_wrlock(&tablelock);

   old_index = index_size;
   if (init) {
      index_size += INIT_INDEX;
   } else {
      index_size += GROW_INDEX;
   }

   /* make new 2d array of translator_path structures */
   if (!(tmp_matrix = ast_calloc(1, sizeof(struct translator_path *) * (index_size)))) {
      goto resize_cleanup;
   }

   for (x = 0; x < index_size; x++) {
      if (!(tmp_matrix[x] = ast_calloc(1, sizeof(struct translator_path) * (index_size)))) {
         goto resize_cleanup;
      }
   }

   /* make new index table */
   if (!(tmp_table = ast_calloc(1, sizeof(unsigned int) * index_size))) {
      goto resize_cleanup;
   }

   /* if everything went well this far, free the old and use the new */
   if (!init) {
      for (x = 0; x < old_index; x++) {
         ast_free(__matrix[x]);
      }
      ast_free(__matrix);

      memcpy(tmp_table, __indextable, sizeof(unsigned int) * old_index);
      ast_free(__indextable);
   }

   /* now copy them over */
   __matrix = tmp_matrix;
   __indextable = tmp_table;

   matrix_rebuild(0);
   ast_rwlock_unlock(&tablelock);
   AST_RWLIST_UNLOCK(&translators);

   return 0;

resize_cleanup:
   ast_rwlock_unlock(&tablelock);
   AST_RWLIST_UNLOCK(&translators);
   if (tmp_matrix) {
      for (x = 0; x < index_size; x++) {
         ast_free(tmp_matrix[x]);
      }
      ast_free(tmp_matrix);
   }
   ast_free(tmp_table);

   return -1;
}

/*!
 * \internal
 * \brief reinitialize the __matrix during matrix rebuild
 *
 * \note must be protected by the translators list lock
 */
static void matrix_clear(void)
{
   int x;
   for (x = 0; x < index_size; x++) {
      memset(__matrix[x], '\0', sizeof(struct translator_path) * (index_size));
   }
}

/*!
 * \internal
 * \brief get a matrix entry
 *
 * \note This function must be protected by the translators list lock
 */
static struct translator_path *matrix_get(unsigned int x, unsigned int y)
{
   return __matrix[x] + y;
}

/*
 * wrappers around the translator routines.
 */

static void destroy(struct ast_trans_pvt *pvt)
{
   struct ast_translator *t = pvt->t;

   if (t->destroy) {
      t->destroy(pvt);
   }
   ao2_cleanup(pvt->f.subclass.format);
   if (pvt->explicit_dst) {
      ao2_ref(pvt->explicit_dst, -1);
      pvt->explicit_dst = NULL;
   }
   ast_free(pvt);
   ast_module_unref(t->module);
}

/*!
 * \brief Allocate the descriptor, required outbuf space,
 * and possibly desc.
 */
static struct ast_trans_pvt *newpvt(struct ast_translator *t, struct ast_format *explicit_dst)
{
   struct ast_trans_pvt *pvt;
   int len;
   char *ofs;

   /*
    * compute the required size adding private descriptor,
    * buffer, AST_FRIENDLY_OFFSET.
    */
   len = sizeof(*pvt) + t->desc_size;
   if (t->buf_size)
      len += AST_FRIENDLY_OFFSET + t->buf_size;
   pvt = ast_calloc(1, len);
   if (!pvt) {
      return NULL;
   }
   pvt->t = t;
   ofs = (char *)(pvt + 1);   /* pointer to data space */
   if (t->desc_size) {     /* first comes the descriptor */
      pvt->pvt = ofs;
      ofs += t->desc_size;
   }
   if (t->buf_size) {/* finally buffer and header */
      pvt->outbuf.c = ofs + AST_FRIENDLY_OFFSET;
   }
   /*
    * If the format has an attribute module, explicit_dst includes the (joined)
    * result of the SDP negotiation. For example with the Opus Codec, the format
    * knows whether both parties want to do forward-error correction (FEC).
    */
   pvt->explicit_dst = ao2_bump(explicit_dst);

   ast_module_ref(t->module);

   /* call local init routine, if present */
   if (t->newpvt && t->newpvt(pvt)) {
      ast_free(pvt);
      ast_module_unref(t->module);
      return NULL;
   }

   /* Setup normal static translation frame. */
   pvt->f.frametype = AST_FRAME_VOICE;
   pvt->f.mallocd = 0;
   pvt->f.offset = AST_FRIENDLY_OFFSET;
   pvt->f.src = pvt->t->name;
   pvt->f.data.ptr = pvt->outbuf.c;

   /*
    * If the translator has not provided a format
    * A) use the joined one,
    * B) use the cached one, or
    * C) create one.
    */
   if (!pvt->f.subclass.format) {
      pvt->f.subclass.format = ao2_bump(pvt->explicit_dst);

      if (!pvt->f.subclass.format && !ast_strlen_zero(pvt->t->format)) {
         pvt->f.subclass.format = ast_format_cache_get(pvt->t->format);
      }

      if (!pvt->f.subclass.format) {
         struct ast_codec *codec = ast_codec_get(t->dst_codec.name,
            t->dst_codec.type, t->dst_codec.sample_rate);
         if (!codec) {
            ast_log(LOG_ERROR, "Unable to get destination codec\n");
            destroy(pvt);
            return NULL;
         }
         pvt->f.subclass.format = ast_format_create(codec);
         ao2_ref(codec, -1);
      }

      if (!pvt->f.subclass.format) {
         ast_log(LOG_ERROR, "Unable to create format\n");
         destroy(pvt);
         return NULL;
      }
   }

   return pvt;
}

/*! \brief framein wrapper, deals with bound checks.  */
static int framein(struct ast_trans_pvt *pvt, struct ast_frame *f)
{
   /* Copy the last in jb timing info to the pvt */
   ast_copy_flags(&pvt->f, f, AST_FRFLAG_HAS_TIMING_INFO);
   pvt->f.ts = f->ts;
   pvt->f.len = f->len;
   pvt->f.seqno = f->seqno;

   if (f->samples == 0) {
      /* Do not log empty audio frame */
      if (!f->src || strcasecmp(f->src, "ast_prod")) {
         ast_log(LOG_WARNING, "no samples for %s\n", pvt->t->name);
      }
   }
   if (pvt->t->buffer_samples) { /* do not pass empty frames to callback */
      if (f->datalen == 0) { /* perform native PLC if available */
         /* If the codec has native PLC, then do that */
         if (!pvt->t->native_plc)
            return 0;
      }
      if (pvt->samples + f->samples > pvt->t->buffer_samples) {
         ast_log(LOG_WARNING, "Out of buffer space\n");
         return -1;
      }
   }
   /* we require a framein routine, wouldn't know how to do
    * it otherwise.
    */
   return pvt->t->framein(pvt, f);
}

/*! \brief generic frameout routine.
 * If samples and datalen are 0, take whatever is in pvt
 * and reset them, otherwise take the values in the caller and
 * leave alone the pvt values.
 */
struct ast_frame *ast_trans_frameout(struct ast_trans_pvt *pvt,
   int datalen, int samples)
{
   struct ast_frame *f = &pvt->f;

   if (samples) {
      f->samples = samples;
   } else {
      if (pvt->samples == 0) {
         return NULL;
      }
      f->samples = pvt->samples;
      pvt->samples = 0;
   }
   if (datalen) {
      f->datalen = datalen;
      f->data.ptr = pvt->outbuf.c;
   } else {
      f->datalen = pvt->datalen;
      if (!f->datalen) {
         f->data.ptr = NULL;
      } else {
         f->data.ptr = pvt->outbuf.c;
      }
      pvt->datalen = 0;
   }

   return ast_frisolate(f);
}

static struct ast_frame *default_frameout(struct ast_trans_pvt *pvt)
{
   return ast_trans_frameout(pvt, 0, 0);
}

/* end of callback wrappers and helpers */

void ast_translator_free_path(struct ast_trans_pvt *p)
{
   struct ast_trans_pvt *pn = p;
   while ( (p = pn) ) {
      pn = p->next;
      destroy(p);
   }
}

/*! \brief Build a chain of translators based upon the given source and dest formats */
struct ast_trans_pvt *ast_translator_build_path(struct ast_format *dst, struct ast_format *src)
{
   struct ast_trans_pvt *head = NULL, *tail = NULL;
   int src_index, dst_index;

   src_index = format2index(src);
   dst_index = format2index(dst);

   if (src_index < 0 || dst_index < 0) {
      ast_log(LOG_WARNING, "No translator path: (%s codec is not valid)\n", src_index < 0 ? "starting" : "ending");
      return NULL;
   }

   AST_RWLIST_RDLOCK(&translators);

   while (src_index != dst_index) {
      struct ast_trans_pvt *cur;
      struct ast_format *explicit_dst = NULL;
      struct ast_translator *t = matrix_get(src_index, dst_index)->step;
      if (!t) {
         ast_log(LOG_WARNING, "No translator path from %s to %s\n",
            ast_format_get_name(src), ast_format_get_name(dst));
         AST_RWLIST_UNLOCK(&translators);
         ast_translator_free_path(head);
         return NULL;
      }
      if ((t->dst_codec.sample_rate == ast_format_get_sample_rate(dst)) && (t->dst_codec.type == ast_format_get_type(dst))) {
         explicit_dst = dst;
      }
      if (!(cur = newpvt(t, explicit_dst))) {
         ast_log(LOG_WARNING, "Failed to build translator step from %s to %s\n",
            ast_format_get_name(src), ast_format_get_name(dst));
         ast_translator_free_path(head);
         AST_RWLIST_UNLOCK(&translators);
         return NULL;
      }
      if (!head) {
         head = cur;
      } else {
         tail->next = cur;
      }
      tail = cur;
      cur->nextin = cur->nextout = ast_tv(0, 0);
      /* Keep going if this isn't the final destination */
      src_index = cur->t->dst_fmt_index;
   }

   AST_RWLIST_UNLOCK(&translators);
   return head;
}

static struct ast_frame *generate_interpolated_slin(struct ast_trans_pvt *p, struct ast_frame *f)
{
   struct ast_frame res = { AST_FRAME_VOICE };

   /*
    * If we've gotten here then we should have an interpolated frame that was not handled
    * by the translation codec. So create an interpolated frame in the appropriate format
    * that was going to be written. This frame might be handled later by other resources.
    * For instance, generic plc.
    *
    * Note, generic plc is currently only available for the format type 'slin' (8KHz only -
    * The generic plc code appears to have been based around that). Generic plc is filled
    * in later on frame write.
    */
   if (!ast_opt_generic_plc || f->datalen != 0 ||
      ast_format_cmp(p->explicit_dst, ast_format_slin) == AST_FORMAT_CMP_NOT_EQUAL) {
      return NULL;
   }

   res.subclass.format = ast_format_cache_get_slin_by_rate(8000); /* ref bumped on dup */
   res.samples = f->samples;
   res.datalen = 0;
   res.data.ptr = NULL;
   res.offset = AST_FRIENDLY_OFFSET;

   return ast_frdup(&res);
}

/*! \brief do the actual translation */
struct ast_frame *ast_translate(struct ast_trans_pvt *path, struct ast_frame *f, int consume)
{
   struct ast_trans_pvt *p = path;
   struct ast_frame *out;
   struct timeval delivery;
   int has_timing_info;
   long ts;
   long len;
   int seqno;

   if (f->frametype == AST_FRAME_RTCP) {
      /* Just pass the feedback to the right callback, if it exists.
       * This "translation" does nothing so return a null frame. */
      struct ast_trans_pvt *tp;
      for (tp = p; tp; tp = tp->next) {
         if (tp->t->feedback)
            tp->t->feedback(tp, f);
      }
      return &ast_null_frame;
   }

   has_timing_info = ast_test_flag(f, AST_FRFLAG_HAS_TIMING_INFO);
   ts = f->ts;
   len = f->len;
   seqno = f->seqno;

   if (!ast_tvzero(f->delivery)) {
      if (!ast_tvzero(path->nextin)) {
         /* Make sure this is in line with what we were expecting */
         if (!ast_tveq(path->nextin, f->delivery)) {
            /* The time has changed between what we expected and this
               most recent time on the new packet.  If we have a
               valid prediction adjust our output time appropriately */
            if (!ast_tvzero(path->nextout)) {
               path->nextout = ast_tvadd(path->nextout,
                          ast_tvsub(f->delivery, path->nextin));
            }
            path->nextin = f->delivery;
         }
      } else {
         /* This is our first pass.  Make sure the timing looks good */
         path->nextin = f->delivery;
         path->nextout = f->delivery;
      }
      /* Predict next incoming sample */
      path->nextin = ast_tvadd(path->nextin, ast_samp2tv(
          f->samples, ast_format_get_sample_rate(f->subclass.format)));
   }
   delivery = f->delivery;
   for (out = f; out && p ; p = p->next) {
      struct ast_frame *current = out;

      do {
         framein(p, current);
         current = AST_LIST_NEXT(current, frame_list);
      } while (current);
      if (out != f) {
         ast_frfree(out);
      }
      out = p->t->frameout(p);
   }

   if (!out) {
      out = generate_interpolated_slin(path, f);
   }

   if (out) {
      /* we have a frame, play with times */
      if (!ast_tvzero(delivery)) {
         struct ast_frame *current = out;

         do {
            /* Regenerate prediction after a discontinuity */
            if (ast_tvzero(path->nextout)) {
               path->nextout = ast_tvnow();
            }

            /* Use next predicted outgoing timestamp */
            current->delivery = path->nextout;

            /* Invalidate prediction if we're entering a silence period */
            if (current->frametype == AST_FRAME_CNG) {
               path->nextout = ast_tv(0, 0);
            /* Predict next outgoing timestamp from samples in this
               frame. */
            } else {
               path->nextout = ast_tvadd(path->nextout, ast_samp2tv(
                  current->samples, ast_format_get_sample_rate(current->subclass.format)));
            }

            if (f->samples != current->samples && ast_test_flag(current, AST_FRFLAG_HAS_TIMING_INFO)) {
               ast_debug(4, "Sample size different %d vs %d\n", f->samples, current->samples);
               ast_clear_flag(current, AST_FRFLAG_HAS_TIMING_INFO);
            }
            current = AST_LIST_NEXT(current, frame_list);
         } while (current);
      } else {
         out->delivery = ast_tv(0, 0);
         ast_set2_flag(out, has_timing_info, AST_FRFLAG_HAS_TIMING_INFO);
         if (has_timing_info) {
            out->ts = ts;
            out->len = len;
            out->seqno = seqno;
         }
         /* Invalidate prediction if we're entering a silence period */
         if (out->frametype == AST_FRAME_CNG) {
            path->nextout = ast_tv(0, 0);
         }
      }
   }
   if (consume) {
      ast_frfree(f);
   }
   return out;
}

/*!
 * \internal
 * \brief Compute the computational cost of a single translation step.
 *
 * \note This function is only used to decide which translation path to
 * use between two translators with identical src and dst formats.  Computational
 * cost acts only as a tie breaker. This is done so hardware translators
 * can naturally have precedence over software translators.
 */
static void generate_computational_cost(struct ast_translator *t, int seconds)
{
   int num_samples = 0;
   struct ast_trans_pvt *pvt;
   struct rusage start;
   struct rusage end;
   int cost;
   int out_rate = t->dst_codec.sample_rate;

   if (!seconds) {
      seconds = 1;
   }

   /* If they don't make samples, give them a terrible score */
   if (!t->sample) {
      ast_debug(3, "Translator '%s' does not produce sample frames.\n", t->name);
      t->comp_cost = 999999;
      return;
   }

   pvt = newpvt(t, NULL);
   if (!pvt) {
      ast_log(LOG_WARNING, "Translator '%s' appears to be broken and will probably fail.\n", t->name);
      t->comp_cost = 999999;
      return;
   }

   getrusage(RUSAGE_SELF, &start);

   /* Call the encoder until we've processed the required number of samples */
   while (num_samples < seconds * out_rate) {
      struct ast_frame *f = t->sample();
      if (!f) {
         ast_log(LOG_WARNING, "Translator '%s' failed to produce a sample frame.\n", t->name);
         destroy(pvt);
         t->comp_cost = 999999;
         return;
      }
      framein(pvt, f);
      ast_frfree(f);
      while ((f = t->frameout(pvt))) {
         num_samples += f->samples;
         ast_frfree(f);
      }
   }

   getrusage(RUSAGE_SELF, &end);

   cost = ((end.ru_utime.tv_sec - start.ru_utime.tv_sec) * 1000000) + end.ru_utime.tv_usec - start.ru_utime.tv_usec;
   cost += ((end.ru_stime.tv_sec - start.ru_stime.tv_sec) * 1000000) + end.ru_stime.tv_usec - start.ru_stime.tv_usec;

   destroy(pvt);

   t->comp_cost = cost / seconds;

   if (!t->comp_cost) {
      t->comp_cost = 1;
   }
}

/*!
 * \internal
 *
 * \brief If no table cost value was pre set by the translator.  An attempt is made to
 * automatically generate that cost value from the cost table based on our src and
 * dst formats.
 *
 * \note This function allows older translators built before the translation cost
 * changed away from using onely computational time to continue to be registered
 * correctly.  It is expected that translators built after the introduction of this
 * function will manually assign their own table cost value.
 *
 * \note This function is safe to use on any audio formats that used to be defined in the
 * first 64 bits of the old bit field codec representation.
 *
 * \retval Table Cost value greater than 0.
 * \retval 0 on error.
 */
static int generate_table_cost(struct ast_codec *src, struct ast_codec *dst)
{
   int src_rate = src->sample_rate;
   int src_ll = 0;
   int dst_rate = dst->sample_rate;
   int dst_ll = 0;

   if ((src->type != AST_MEDIA_TYPE_AUDIO) ||
       (dst->type != AST_MEDIA_TYPE_AUDIO)) {
      /* This method of generating table cost is limited to audio.
       * Translators for media other than audio must manually set their
       * table cost. */
      return 0;
   }

   src_ll = !strcmp(src->name, "slin");
   dst_ll = !strcmp(dst->name, "slin");
   if (src_ll) {
      if (dst_ll && (src_rate == dst_rate)) {
         return AST_TRANS_COST_LL_LL_ORIGSAMP;
      } else if (!dst_ll && (src_rate == dst_rate)) {
         return AST_TRANS_COST_LL_LY_ORIGSAMP;
      } else if (dst_ll && (src_rate < dst_rate)) {
         return AST_TRANS_COST_LL_LL_UPSAMP;
      } else if (!dst_ll && (src_rate < dst_rate)) {
         return AST_TRANS_COST_LL_LY_UPSAMP;
      } else if (dst_ll && (src_rate > dst_rate)) {
         return AST_TRANS_COST_LL_LL_DOWNSAMP;
      } else if (!dst_ll && (src_rate > dst_rate)) {
         return AST_TRANS_COST_LL_LY_DOWNSAMP;
      } else {
         return AST_TRANS_COST_LL_UNKNOWN;
      }
   } else {
      if (dst_ll && (src_rate == dst_rate)) {
         return AST_TRANS_COST_LY_LL_ORIGSAMP;
      } else if (!dst_ll && (src_rate == dst_rate)) {
         return AST_TRANS_COST_LY_LY_ORIGSAMP;
      } else if (dst_ll && (src_rate < dst_rate)) {
         return AST_TRANS_COST_LY_LL_UPSAMP;
      } else if (!dst_ll && (src_rate < dst_rate)) {
         return AST_TRANS_COST_LY_LY_UPSAMP;
      } else if (dst_ll && (src_rate > dst_rate)) {
         return AST_TRANS_COST_LY_LL_DOWNSAMP;
      } else if (!dst_ll && (src_rate > dst_rate)) {
         return AST_TRANS_COST_LY_LY_DOWNSAMP;
      } else {
         return AST_TRANS_COST_LY_UNKNOWN;
      }
   }
}

/*!
 * \brief rebuild a translation matrix.
 * \note This function expects the list of translators to be locked
*/
static void matrix_rebuild(int samples)
{
   struct ast_translator *t;
   int newtablecost;
   int x;      /* source format index */
   int y;      /* intermediate format index */
   int z;      /* destination format index */

   ast_debug(1, "Resetting translation matrix\n");

   matrix_clear();

   /* first, compute all direct costs */
   AST_RWLIST_TRAVERSE(&translators, t, list) {
      if (!t->active) {
         continue;
      }

      x = t->src_fmt_index;
      z = t->dst_fmt_index;

      if (samples) {
         generate_computational_cost(t, samples);
      }

      /* This new translator is the best choice if any of the below are true.
       * 1. no translation path is set between x and z yet.
       * 2. the new table cost is less.
       * 3. the new computational cost is less.  Computational cost is only used
       *    to break a tie between two identical translation paths.
       */
      if (!matrix_get(x, z)->step ||
         (t->table_cost < matrix_get(x, z)->step->table_cost) ||
         (t->comp_cost < matrix_get(x, z)->step->comp_cost)) {

         matrix_get(x, z)->step = t;
         matrix_get(x, z)->table_cost = t->table_cost;
      }
   }

   /*
    * For each triple x, y, z of distinct formats, check if there is
    * a path from x to z through y which is cheaper than what is
    * currently known, and in case, update the matrix.
    * Repeat until the matrix is stable.
    */
   for (;;) {
      int changed = 0;
      for (x = 0; x < cur_max_index; x++) {      /* source format */
         for (y = 0; y < cur_max_index; y++) {  /* intermediate format */
            if (x == y) {                      /* skip ourselves */
               continue;
            }
            for (z = 0; z < cur_max_index; z++) {  /* dst format */
               if ((z == x || z == y) ||        /* skip null conversions */
                  !matrix_get(x, y)->step ||   /* no path from x to y */
                  !matrix_get(y, z)->step) {   /* no path from y to z */
                  continue;
               }

               /* calculate table cost from x->y->z */
               newtablecost = matrix_get(x, y)->table_cost + matrix_get(y, z)->table_cost;

               /* if no step already exists between x and z OR the new cost of using the intermediate
                * step is cheaper, use this step. */
               if (!matrix_get(x, z)->step || (newtablecost < matrix_get(x, z)->table_cost)) {
                  matrix_get(x, z)->step = matrix_get(x, y)->step;
                  matrix_get(x, z)->table_cost = newtablecost;
                  matrix_get(x, z)->multistep = 1;
                  changed++;

                  if (DEBUG_ATLEAST(10)) {
                     struct ast_codec *x_codec = index2codec(x);
                     struct ast_codec *y_codec = index2codec(y);
                     struct ast_codec *z_codec = index2codec(z);

                     ast_log(LOG_DEBUG,
                        "Discovered %u cost path from %s to %s, via %s\n",
                        matrix_get(x, z)->table_cost, x_codec->name,
                        y_codec->name, z_codec->name);

                     ao2_ref(x_codec, -1);
                     ao2_ref(y_codec, -1);
                     ao2_ref(z_codec, -1);
                  }
               }
            }
         }
      }
      if (!changed) {
         break;
      }
   }
}

static void codec_append_name(const struct ast_codec *codec, struct ast_str **buf)
{
   if (codec) {
      ast_str_append(buf, 0, "(%s@%u)", codec->name, codec->sample_rate);
   } else {
      ast_str_append(buf, 0, "(nothing)");
   }
}

const char *ast_translate_path_to_str(struct ast_trans_pvt *p, struct ast_str **str)
{
   if (!p || !p->t) {
      return "";
   }

   ast_str_reset(*str);
   codec_append_name(&p->t->src_codec, str);
   while (p) {
      ast_str_append(str, 0, "->");
      codec_append_name(&p->t->dst_codec, str);
      p = p->next;
   }

   return ast_str_buffer(*str);
}

static char *complete_trans_path_choice(const char *word)
{
   int i = 1;
   int wordlen = strlen(word);
   struct ast_codec *codec;

   while ((codec = ast_codec_get_by_id(i))) {
      ++i;
      if (codec->type != AST_MEDIA_TYPE_AUDIO) {
         ao2_ref(codec, -1);
         continue;
      }
      if (!strncasecmp(word, codec->name, wordlen)) {
         if (ast_cli_completion_add(ast_strdup(codec->name))) {
            ao2_ref(codec, -1);
            break;
         }
      }
      ao2_ref(codec, -1);
   }

   return NULL;
}

static void handle_cli_recalc(struct ast_cli_args *a)
{
   int time = a->argv[4] ? atoi(a->argv[4]) : 1;

   if (time <= 0) {
      ast_cli(a->fd, "         Recalc must be greater than 0.  Defaulting to 1.\n");
      time = 1;
   }

   if (time > MAX_RECALC) {
      ast_cli(a->fd, "         Maximum limit of recalc exceeded by %d, truncating value to %d\n", time - MAX_RECALC, MAX_RECALC);
      time = MAX_RECALC;
   }
   ast_cli(a->fd, "         Recalculating Codec Translation (number of sample seconds: %d)\n\n", time);
   AST_RWLIST_WRLOCK(&translators);
   matrix_rebuild(time);
   AST_RWLIST_UNLOCK(&translators);
}

static char *handle_show_translation_table(struct ast_cli_args *a)
{
   int x, y, i, k;
   int longest = 7; /* slin192 */
   int max_codec_index = 0, curlen = 0;
   struct ast_str *out = ast_str_create(1024);
   struct ast_codec *codec;

   /* Get the length of the longest (usable?) codec name,
      so we know how wide the left side should be */
   for (i = 1; (codec = ast_codec_get_by_id(i)); ao2_ref(codec, -1), ++i) {
      ++max_codec_index;
      if (codec->type != AST_MEDIA_TYPE_AUDIO) {
         continue;
      }
      curlen = strlen(codec->name);
      if (curlen > longest) {
         longest = curlen;
      }
   }

   AST_RWLIST_RDLOCK(&translators);
   ast_cli(a->fd, "         Translation times between formats (in microseconds) for one second of data\n");
   ast_cli(a->fd, "          Source Format (Rows) Destination Format (Columns)\n\n");

   for (i = 0; i <= max_codec_index; i++) {
      struct ast_codec *row = i ? ast_codec_get_by_id(i) : NULL;

      x = -1;
      if ((i > 0) && (row->type != AST_MEDIA_TYPE_AUDIO)) {
         ao2_ref(row, -1);
         continue;
      }

      if ((i > 0) && (x = codec2index(row)) == -1) {
         ao2_ref(row, -1);
         continue;
      }

      ast_str_set(&out, 0, " ");
      for (k = 0; k <= max_codec_index; k++) {
         int adjust = 0;
         struct ast_codec *col = k ? ast_codec_get_by_id(k) : NULL;

         y = -1;
         if ((k > 0) && (col->type != AST_MEDIA_TYPE_AUDIO)) {
            ao2_ref(col, -1);
            continue;
         }

         if ((k > 0) && (y = codec2index(col)) == -1) {
            ao2_ref(col, -1);
            continue;
         }

         if (k > 0) {
            curlen = strlen(col->name);
            if (!strcmp(col->name, "slin") ||
               !strcmp(col->name, "speex") ||
               !strcmp(col->name, "silk")) {
               adjust = log10(col->sample_rate / 1000) + 1;
               curlen = curlen + adjust;
            }
         }

         if (curlen < 5) {
            curlen = 5;
         }

         if (x >= 0 && y >= 0 && matrix_get(x, y)->step) {
            /* Actual codec output */
            ast_str_append(&out, 0, "%*u", curlen + 1, (matrix_get(x, y)->table_cost/100));
         } else if (i == 0 && k > 0) {
            /* Top row - use a dynamic size */
            if (!strcmp(col->name, "slin") ||
               !strcmp(col->name, "speex") ||
               !strcmp(col->name, "silk")) {
               ast_str_append(&out, 0, "%*s%u", curlen - adjust + 1,
                  col->name, col->sample_rate / 1000);
            } else {
               ast_str_append(&out, 0, "%*s", curlen + 1, col->name);
            }
         } else if (k == 0 && i > 0) {
            /* Left column - use a static size. */
            if (!strcmp(row->name, "slin") ||
               !strcmp(row->name, "speex") ||
               !strcmp(row->name, "silk")) {
               int adjust_row = log10(row->sample_rate / 1000) + 1;
               ast_str_append(&out, 0, "%*s%u", longest - adjust_row,
                  row->name, row->sample_rate / 1000);
            } else {
               ast_str_append(&out, 0, "%*s", longest, row->name);
            }
         } else if (x >= 0 && y >= 0) {
            /* Codec not supported */
            ast_str_append(&out, 0, "%*s", curlen + 1, "-");
         } else {
            /* Upper left hand corner */
            ast_str_append(&out, 0, "%*s", longest, "");
         }
         ao2_cleanup(col);
      }
      ast_str_append(&out, 0, "\n");
      ast_cli(a->fd, "%s", ast_str_buffer(out));
      ao2_cleanup(row);
   }
   ast_free(out);
   AST_RWLIST_UNLOCK(&translators);
   return CLI_SUCCESS;
}

static char *handle_show_translation_path(struct ast_cli_args *a, const char *codec_name, unsigned int sample_rate)
{
   int i = 1;
   struct ast_str *str = ast_str_alloca(1024);
   struct ast_translator *step;
   struct ast_codec *dst_codec;
   struct ast_codec *src_codec = ast_codec_get(codec_name, AST_MEDIA_TYPE_AUDIO, sample_rate);

   if (!src_codec) {
      ast_cli(a->fd, "Source codec \"%s\" is not found.\n", codec_name);
      return CLI_FAILURE;
   }

   AST_RWLIST_RDLOCK(&translators);
   ast_cli(a->fd, "--- Translation paths SRC Codec \"%s\" sample rate %u ---\n",
      codec_name, src_codec->sample_rate);

   while ((dst_codec = ast_codec_get_by_id(i))) {
      int src, dst;
      char src_buffer[64];
      char dst_buffer[64];

      ++i;
      if (src_codec == dst_codec ||
          dst_codec->type != AST_MEDIA_TYPE_AUDIO) {
         ao2_ref(dst_codec, -1);
         continue;
      }

      dst = codec2index(dst_codec);
      src = codec2index(src_codec);

      if (src < 0 || dst < 0) {
         ast_str_set(&str, 0, "No Translation Path");
      } else {
         step = matrix_get(src, dst)->step;

         if (step) {
            codec_append_name(&step->src_codec, &str);
            while (src != dst) {
               src = step->dst_fmt_index;
               step = matrix_get(src, dst)->step;
               if (!step) {
                  ast_str_append(&str, 0, "->");
                  codec_append_name(dst_codec, &str);
                  break;
               }
               ast_str_append(&str, 0, "->");
               codec_append_name(&step->src_codec, &str);
            }
         }
      }

      snprintf(src_buffer, sizeof(src_buffer), "%s:%u", src_codec->name, src_codec->sample_rate);
      snprintf(dst_buffer, sizeof(dst_buffer), "%s:%u", dst_codec->name, dst_codec->sample_rate);
      ast_cli(a->fd, "\t%-16.16s To %-16.16s: %-60.60s\n",
         src_buffer, dst_buffer, ast_str_buffer(str));
      ast_str_reset(str);
      ao2_ref(dst_codec, -1);
   }
   AST_RWLIST_UNLOCK(&translators);
   ao2_ref(src_codec, -1);
   return CLI_SUCCESS;
}

static char *handle_cli_core_show_translation(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
   static const char * const option[] = { "recalc", "paths", NULL };

   switch (cmd) {
   case CLI_INIT:
      e->command = "core show translation";
      e->usage =
         "Usage: 'core show translation' can be used in two ways.\n"
         "       1. 'core show translation [recalc [<recalc seconds>]]\n"
         "          Displays known codec translators and the cost associated\n"
         "          with each conversion.  If the argument 'recalc' is supplied along\n"
         "          with optional number of seconds to test a new test will be performed\n"
         "          as the chart is being displayed.\n"
         "       2. 'core show translation paths [codec [sample_rate]]'\n"
         "           This will display all the translation paths associated with a codec.\n"
         "           If a codec has multiple sample rates, the sample rate must be\n"
         "           provided as well.\n";
      return NULL;
   case CLI_GENERATE:
      if (a->pos == 3) {
         return ast_cli_complete(a->word, option, -1);
      }
      if (a->pos == 4 && !strcasecmp(a->argv[3], option[1])) {
         return complete_trans_path_choice(a->word);
      }
      /* BUGBUG - add tab completion for sample rates */
      return NULL;
   }

   if (a->argc > 6)
      return CLI_SHOWUSAGE;

   if (a->argv[3] && !strcasecmp(a->argv[3], option[1]) && a->argc == 5) { /* show paths */
      return handle_show_translation_path(a, a->argv[4], 0);
   } else if (a->argv[3] && !strcasecmp(a->argv[3], option[1]) && a->argc == 6) {
      unsigned int sample_rate;
      if (sscanf(a->argv[5], "%30u", &sample_rate) != 1) {
         ast_cli(a->fd, "Invalid sample rate: %s.\n", a->argv[5]);
         return CLI_FAILURE;
      }
      return handle_show_translation_path(a, a->argv[4], sample_rate);
   } else if (a->argv[3] && !strcasecmp(a->argv[3], option[0])) { /* recalc and then fall through to show table */
      handle_cli_recalc(a);
   } else if (a->argc > 3) { /* wrong input */
      return CLI_SHOWUSAGE;
   }

   return handle_show_translation_table(a);
}

static struct ast_cli_entry cli_translate[] = {
   AST_CLI_DEFINE(handle_cli_core_show_translation, "Display translation matrix")
};

/*! \brief register codec translator */
int __ast_register_translator(struct ast_translator *t, struct ast_module *mod)
{
   struct ast_translator *u;
   char tmp[80];
   RAII_VAR(struct ast_codec *, src_codec, NULL, ao2_cleanup);
   RAII_VAR(struct ast_codec *, dst_codec, NULL, ao2_cleanup);

   src_codec = ast_codec_get(t->src_codec.name, t->src_codec.type, t->src_codec.sample_rate);
   if (!src_codec) {
      ast_assert(0);
      ast_log(LOG_WARNING, "Failed to register translator: unknown source codec %s\n", t->src_codec.name);
      return -1;
   }

   dst_codec = ast_codec_get(t->dst_codec.name, t->dst_codec.type, t->dst_codec.sample_rate);
   if (!dst_codec) {
      ast_log(LOG_WARNING, "Failed to register translator: unknown destination codec %s\n", t->dst_codec.name);
      return -1;
   }

   if (add_codec2index(src_codec) || add_codec2index(dst_codec)) {
      if (matrix_resize(0)) {
         ast_log(LOG_WARNING, "Translator matrix can not represent any more translators.  Out of resources.\n");
         return -1;
      }
      add_codec2index(src_codec);
      add_codec2index(dst_codec);
   }

   if (!mod) {
      ast_log(LOG_WARNING, "Missing module pointer, you need to supply one\n");
      return -1;
   }

   if (!t->buf_size) {
      ast_log(LOG_WARNING, "empty buf size, you need to supply one\n");
      return -1;
   }
   if (!t->table_cost && !(t->table_cost = generate_table_cost(src_codec, dst_codec))) {
      ast_log(LOG_WARNING, "Table cost could not be generated for %s, "
         "Please set table_cost variable on translator.\n", t->name);
      return -1;
   }

   t->module = mod;
   t->src_fmt_index = codec2index(src_codec);
   t->dst_fmt_index = codec2index(dst_codec);
   t->active = 1;

   if (t->src_fmt_index < 0 || t->dst_fmt_index < 0) {
      ast_log(LOG_WARNING, "Invalid translator path: (%s codec is not valid)\n", t->src_fmt_index < 0 ? "starting" : "ending");
      return -1;
   }
   if (t->src_fmt_index >= cur_max_index) {
      ast_log(LOG_WARNING, "Source codec %s is larger than cur_max_index\n", t->src_codec.name);
      return -1;
   }

   if (t->dst_fmt_index >= cur_max_index) {
      ast_log(LOG_WARNING, "Destination codec %s is larger than cur_max_index\n", t->dst_codec.name);
      return -1;
   }

   if (t->buf_size) {
      /*
       * Align buf_size properly, rounding up to the machine-specific
       * alignment for pointers.
       */
      struct _test_align { void *a, *b; } p;
      int align = (char *)&p.b - (char *)&p.a;

      t->buf_size = ((t->buf_size + align - 1) / align) * align;
   }

   if (t->frameout == NULL) {
      t->frameout = default_frameout;
   }

   generate_computational_cost(t, 1);

   ast_verb(2, "Registered translator '%s' from codec %s to %s, table cost, %d, computational cost %d\n",
       term_color(tmp, t->name, COLOR_MAGENTA, COLOR_BLACK, sizeof(tmp)),
       t->src_codec.name, t->dst_codec.name, t->table_cost, t->comp_cost);

   AST_RWLIST_WRLOCK(&translators);

   /* find any existing translators that provide this same srcfmt/dstfmt,
      and put this one in order based on computational cost */
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&translators, u, list) {
      if ((u->src_fmt_index == t->src_fmt_index) &&
          (u->dst_fmt_index == t->dst_fmt_index) &&
          (u->comp_cost > t->comp_cost)) {
         AST_RWLIST_INSERT_BEFORE_CURRENT(t, list);
         t = NULL;
         break;
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;

   /* if no existing translator was found for this codec combination,
      add it to the beginning of the list */
   if (t) {
      AST_RWLIST_INSERT_HEAD(&translators, t, list);
   }

   matrix_rebuild(0);

   AST_RWLIST_UNLOCK(&translators);

   return 0;
}

/*! \brief unregister codec translator */
int ast_unregister_translator(struct ast_translator *t)
{
   char tmp[80];
   struct ast_translator *u;
   int found = 0;

   AST_RWLIST_WRLOCK(&translators);
   AST_RWLIST_TRAVERSE_SAFE_BEGIN(&translators, u, list) {
      if (u == t) {
         AST_RWLIST_REMOVE_CURRENT(list);
         ast_verb(2, "Unregistered translator '%s' from codec %s to %s\n",
            term_color(tmp, t->name, COLOR_MAGENTA, COLOR_BLACK, sizeof(tmp)),
            t->src_codec.name, t->dst_codec.name);
         found = 1;
         break;
      }
   }
   AST_RWLIST_TRAVERSE_SAFE_END;

   if (found && !ast_shutting_down()) {
      matrix_rebuild(0);
   }

   AST_RWLIST_UNLOCK(&translators);

   return (u ? 0 : -1);
}

void ast_translator_activate(struct ast_translator *t)
{
   AST_RWLIST_WRLOCK(&translators);
   t->active = 1;
   matrix_rebuild(0);
   AST_RWLIST_UNLOCK(&translators);
}

void ast_translator_deactivate(struct ast_translator *t)
{
   AST_RWLIST_WRLOCK(&translators);
   t->active = 0;
   matrix_rebuild(0);
   AST_RWLIST_UNLOCK(&translators);
}

/*! Calculate the absolute difference between sample rate of two formats. */
#define format_sample_rate_absdiff(fmt1, fmt2) ({ \
   unsigned int rate1 = ast_format_get_sample_rate(fmt1); \
   unsigned int rate2 = ast_format_get_sample_rate(fmt2); \
   (rate1 > rate2 ? rate1 - rate2 : rate2 - rate1); \
})

/*! \brief Calculate our best translator source format, given costs, and a desired destination */
int ast_translator_best_choice(struct ast_format_cap *dst_cap,
   struct ast_format_cap *src_cap,
   struct ast_format **dst_fmt_out,
   struct ast_format **src_fmt_out)
{
   unsigned int besttablecost = INT_MAX;
   unsigned int beststeps = INT_MAX;
   struct ast_format *fmt;
   struct ast_format *dst;
   struct ast_format *src;
   RAII_VAR(struct ast_format *, best, NULL, ao2_cleanup);
   RAII_VAR(struct ast_format *, bestdst, NULL, ao2_cleanup);
   struct ast_format_cap *joint_cap;
   int i;
   int j;

   if (ast_format_cap_empty(dst_cap) || ast_format_cap_empty(src_cap)) {
      ast_log(LOG_ERROR, "Cannot determine best translation path since one capability supports no formats\n");
      return -1;
   }

   joint_cap = ast_format_cap_alloc(AST_FORMAT_CAP_FLAG_DEFAULT);
   if (!joint_cap) {
      return -1;
   }
   ast_format_cap_get_compatible(dst_cap, src_cap, joint_cap);

   for (i = 0; i < ast_format_cap_count(joint_cap); ++i, ao2_cleanup(fmt)) {
      fmt = ast_format_cap_get_format(joint_cap, i);
      if (!fmt
         || ast_format_get_type(fmt) != AST_MEDIA_TYPE_AUDIO) {
         continue;
      }

      if (!best
         || ast_format_get_sample_rate(best) < ast_format_get_sample_rate(fmt)) {
         ao2_replace(best, fmt);
      }
   }
   ao2_ref(joint_cap, -1);

   if (best) {
      ao2_replace(*dst_fmt_out, best);
      ao2_replace(*src_fmt_out, best);
      return 0;
   }

   /* need to translate */
   AST_RWLIST_RDLOCK(&translators);
   for (i = 0; i < ast_format_cap_count(dst_cap); ++i, ao2_cleanup(dst)) {
      dst = ast_format_cap_get_format(dst_cap, i);
      if (!dst
         || ast_format_get_type(dst) != AST_MEDIA_TYPE_AUDIO) {
         continue;
      }

      for (j = 0; j < ast_format_cap_count(src_cap); ++j, ao2_cleanup(src)) {
         int x;
         int y;

         src = ast_format_cap_get_format(src_cap, j);
         if (!src
            || ast_format_get_type(src) != AST_MEDIA_TYPE_AUDIO) {
            continue;
         }

         x = format2index(src);
         y = format2index(dst);
         if (x < 0 || y < 0) {
            continue;
         }
         if (!matrix_get(x, y) || !(matrix_get(x, y)->step)) {
            continue;
         }
         if (matrix_get(x, y)->table_cost < besttablecost
            || matrix_get(x, y)->multistep < beststeps) {
            /* better than what we have so far */
            ao2_replace(best, src);
            ao2_replace(bestdst, dst);
            besttablecost = matrix_get(x, y)->table_cost;
            beststeps = matrix_get(x, y)->multistep;
         } else if (matrix_get(x, y)->table_cost == besttablecost
               && matrix_get(x, y)->multistep == beststeps) {
            unsigned int gap_selected = format_sample_rate_absdiff(best, bestdst);
            unsigned int gap_current = format_sample_rate_absdiff(src, dst);

            if (gap_current < gap_selected) {
               /* better than what we have so far */
               ao2_replace(best, src);
               ao2_replace(bestdst, dst);
               besttablecost = matrix_get(x, y)->table_cost;
               beststeps = matrix_get(x, y)->multistep;
            }
         }
      }
   }
   AST_RWLIST_UNLOCK(&translators);

   if (!best) {
      return -1;
   }
   ao2_replace(*dst_fmt_out, bestdst);
   ao2_replace(*src_fmt_out, best);
   return 0;
}

unsigned int ast_translate_path_steps(struct ast_format *dst_format, struct ast_format *src_format)
{
   unsigned int res = -1;
   /* convert bitwise format numbers into array indices */
   int src = format2index(src_format);
   int dest = format2index(dst_format);

   if (src < 0 || dest < 0) {
      ast_log(LOG_WARNING, "No translator path: (%s codec is not valid)\n", src < 0 ? "starting" : "ending");
      return -1;
   }
   AST_RWLIST_RDLOCK(&translators);

   if (matrix_get(src, dest)->step) {
      res = matrix_get(src, dest)->multistep + 1;
   }

   AST_RWLIST_UNLOCK(&translators);

   return res;
}

static void check_translation_path(
   struct ast_format_cap *dest, struct ast_format_cap *src,
   struct ast_format_cap *result, struct ast_format *src_fmt,
   enum ast_media_type type)
{
   int index, src_index = format2index(src_fmt);
   /* For a given source format, traverse the list of
      known formats to determine whether there exists
      a translation path from the source format to the
      destination format. */
   for (index = 0; (src_index >= 0) && index < cur_max_index; index++) {
      struct ast_codec *codec = index2codec(index);
      RAII_VAR(struct ast_format *, fmt, ast_format_create(codec), ao2_cleanup);

      ao2_ref(codec, -1);

      if (ast_format_get_type(fmt) != type) {
         continue;
      }

      /* if this is not a desired format, nothing to do */
      if (ast_format_cap_iscompatible_format(dest, fmt) == AST_FORMAT_CMP_NOT_EQUAL) {
         continue;
      }

      /* if the source is supplying this format, then
         we can leave it in the result */
      if (ast_format_cap_iscompatible_format(src, fmt) == AST_FORMAT_CMP_EQUAL) {
         continue;
      }

      /* if we don't have a translation path from the src
         to this format, remove it from the result */
      if (!matrix_get(src_index, index)->step) {
         ast_format_cap_remove(result, fmt);
         continue;
      }

      /* now check the opposite direction */
      if (!matrix_get(index, src_index)->step) {
         ast_format_cap_remove(result, fmt);
      }
   }

}

void ast_translate_available_formats(struct ast_format_cap *dest, struct ast_format_cap *src, struct ast_format_cap *result)
{
   struct ast_format *cur_dest, *cur_src;
   int index;

   for (index = 0; index < ast_format_cap_count(dest); ++index) {
      if (!(cur_dest = ast_format_cap_get_format(dest, index))) {
         continue;
      }

      /* We give preference to a joint format structure if possible */
      if ((cur_src = ast_format_cap_get_compatible_format(src, cur_dest))) {
         ast_format_cap_append(result, cur_src, 0);
         ao2_ref(cur_src, -1);
      } else {
         /* Otherwise we just use the destination format */
         ast_format_cap_append(result, cur_dest, 0);
      }
      ao2_ref(cur_dest, -1);
   }

   /* if we don't have a source format, we just have to try all
      possible destination formats */
   if (!src) {
      return;
   }

   for (index = 0; index < ast_format_cap_count(src); ++index) {
      if (!(cur_src = ast_format_cap_get_format(src, index))) {
         continue;
      }

      AST_RWLIST_RDLOCK(&translators);
      check_translation_path(dest, src, result,
                   cur_src, AST_MEDIA_TYPE_AUDIO);
      check_translation_path(dest, src, result,
                   cur_src, AST_MEDIA_TYPE_VIDEO);
      AST_RWLIST_UNLOCK(&translators);
      ao2_ref(cur_src, -1);
   }
}

static void translate_shutdown(void)
{
   int x;
   ast_cli_unregister_multiple(cli_translate, ARRAY_LEN(cli_translate));

   ast_rwlock_wrlock(&tablelock);
   for (x = 0; x < index_size; x++) {
      ast_free(__matrix[x]);
   }
   ast_free(__matrix);
   __matrix = NULL;
   ast_free(__indextable);
   __indextable = NULL;
   ast_rwlock_unlock(&tablelock);
   ast_rwlock_destroy(&tablelock);
}

int ast_translate_init(void)
{
   int res = 0;
   ast_rwlock_init(&tablelock);
   res = matrix_resize(1);
   res |= ast_cli_register_multiple(cli_translate, ARRAY_LEN(cli_translate));
   ast_register_cleanup(translate_shutdown);
   return res;
}