diff --git a/src/cache.c b/src/cache.c
index 8b45fc31..8290a122 100644
--- a/src/cache.c
+++ b/src/cache.c
@@ -93,6 +93,19 @@ struct cache_artwork_stash
   uint8_t *data;
 };
 
+struct cache_xcode_job
+{
+  const char *format;
+  char *file_path;
+  int file_id;
+
+  struct event *ev;
+  bool is_encoding;
+
+  struct evbuffer *header;
+};
+
+
 /* --------------------------------- GLOBALS -------------------------------- */
 
 // cache thread
@@ -188,12 +201,13 @@ static struct cache_db_def cache_artwork_db_def[] = {
 
 // Transcoding cache
 #define CACHE_XCODE_VERSION 1
+#define CACHE_XCODE_NTHREADS 4
+#define CACHE_XCODE_FORMAT_MP4 "mp4"
 static sqlite3 *cache_xcode_hdl;
 static struct event *cache_xcode_updateev;
 static struct event *cache_xcode_prepareev;
+static struct cache_xcode_job cache_xcode_jobs[CACHE_XCODE_NTHREADS];
 static bool cache_xcode_is_enabled;
-static bool cache_xcode_prepare_is_running;
-static int cache_xcode_last_file;
 static struct cache_db_def cache_xcode_db_def[] = {
   DB_DEF_ADMIN,
   {
@@ -212,7 +226,8 @@ static struct cache_db_def cache_xcode_db_def[] = {
     "   timestamp          INTEGER DEFAULT 0,"
     "   file_id            INTEGER DEFAULT 0,"
     "   format             VARCHAR(255) NOT NULL,"
-    "   header             BLOB"
+    "   header             BLOB,"
+    "   UNIQUE(file_id, format) ON CONFLICT REPLACE"
     ");",
     "DROP TABLE IF EXISTS data;",
   },
@@ -856,6 +871,24 @@ cache_daap_update_cb(int fd, short what, void *arg)
   DPRINTF(E_INFO, L_CACHE, "DAAP cache updated\n");
 }
 
+
+/* ----------------------- Caching of transcoded data ----------------------- */
+
+static void
+xcode_job_clear(struct cache_xcode_job *job)
+{
+  free(job->file_path);
+  if (job->header)
+    evbuffer_free(job->header);
+
+  // Can't just memset to zero, because *ev is persistent
+  job->format = NULL;
+  job->file_path = NULL;
+  job->file_id = 0;
+  job->header = NULL;
+  job->is_encoding = false;
+}
+
 static enum command_state
 xcode_header_get(void *arg, int *retval)
 {
@@ -934,7 +967,7 @@ xcode_add_entry(sqlite3 *hdl, uint32_t id, uint32_t ts, const char *path)
   char *errmsg;
   int ret;
 
-  DPRINTF(E_LOG, L_CACHE, "Adding xcode file id %d, path '%s'\n", id, path);
+  DPRINTF(E_SPAM, L_CACHE, "Adding xcode file id %d, path '%s'\n", id, path);
 
   query = sqlite3_mprintf(Q_TMPL, id, ts, path);
 
@@ -960,7 +993,7 @@ xcode_del_entry(sqlite3 *hdl, uint32_t id)
   char *errmsg;
   int ret;
 
-  DPRINTF(E_LOG, L_CACHE, "Deleting xcode file id %d\n", id);
+  DPRINTF(E_SPAM, L_CACHE, "Deleting xcode file id %d\n", id);
 
   sqlite3_snprintf(sizeof(query), query, Q_TMPL_FILES, (int)id);
   ret = sqlite3_exec(hdl, query, NULL, NULL, &errmsg);
@@ -1006,8 +1039,11 @@ xcode_sync_with_files(sqlite3 *hdl)
   size_t cachelist_len = 0;
   struct query_params qp = { .type = Q_ITEMS, .filter = "f.data_kind = 0", .order = "f.id" };
   struct db_media_file_info dbmfi;
+  struct db_media_file_info *rowA;
+  struct cachelist *rowB;
   uint32_t id;
   uint32_t ts;
+  int cmp;
   int i;
   int ret;
 
@@ -1033,42 +1069,47 @@ xcode_sync_with_files(sqlite3 *hdl)
   if (ret < 0)
     goto error;
 
-  // Loop while either list has remaining items
-  i = 0;
-  while (1)
+  // Loop while either list ("A" files list, "B" cache list) has remaining items
+  for(i = 0, cmp = 0;;)
     {
-      ret = db_query_fetch_file(&dbmfi, &qp);
-      if (ret != 0) // At end of files table (or error occured)
-	{
-	  for (; i < cachelist_len; i++)
-	    xcode_del_entry(hdl, cachelist[i].id);
+      if (cmp <= 0)
+        rowA = (db_query_fetch_file(&dbmfi, &qp) == 0) ? &dbmfi : NULL;;
+      if (cmp >= 0)
+        rowB = (i < cachelist_len) ? &cachelist[i++] : NULL;
+      if (!rowA && !rowB)
+        break; // Done with both lists
 
-	  break;
+#if 0
+      if (rowA)
+	DPRINTF(E_DBG, L_CACHE, "cmp %d, rowA->id %s\n", cmp, rowA->id);
+      if (rowB)
+	DPRINTF(E_DBG, L_CACHE, "cmp %d, rowB->id %u, i %d, cachelist_len %zu\n", cmp, rowB->id, i, cachelist_len);
+#endif
+
+      if (rowA)
+	{
+	  safe_atou32(rowA->id, &id);
+	  safe_atou32(rowA->time_modified, &ts);
 	}
 
-      safe_atou32(dbmfi.id, &id);
-      safe_atou32(dbmfi.time_modified, &ts);
-
-      if (i == cachelist_len || cachelist[i].id > id) // At end of cache table or new file
+      cmp = 0; // In both lists - unless:
+      if (!rowB || (rowA && rowB->id > id)) // A had an item not in B
 	{
-	  xcode_add_entry(hdl, id, ts, dbmfi.path);
+	  xcode_add_entry(hdl, id, ts, rowA->path);
+	  cmp = -1;
 	}
-      else if (cachelist[i].id < id) // Removed file
+      else if (!rowA || (rowB && rowB->id < id)) // B had an item not in A
 	{
-	  xcode_del_entry(hdl, cachelist[i].id);
-	  i++;
+	  xcode_del_entry(hdl, rowB->id);
+	  cmp = 1;
 	}
-      else if (cachelist[i].id == id && cachelist[i].ts < ts) // Modified file
+      else if (rowB->id == id && rowB->ts < ts) // Item in B is too old
 	{
-	  xcode_del_entry(hdl, cachelist[i].id);
-	  xcode_add_entry(hdl, id, ts, dbmfi.path);
-	  i++;
-	}
-      else // Found in both tables and timestamp in cache table is adequate
-	{
-	  i++;
+	  xcode_del_entry(hdl, rowB->id);
+	  xcode_add_entry(hdl, id, ts, rowA->path);
 	}
     }
+
   db_query_end(&qp);
 
   free(cachelist);
@@ -1081,135 +1122,157 @@ xcode_sync_with_files(sqlite3 *hdl)
 }
 
 static int
-xcode_prepare_header(sqlite3 *hdl, const char *format, int id, const char *path)
+xcode_header_save(sqlite3 *hdl, int file_id, const char *format, uint8_t *data, size_t datalen)
 {
 #define Q_TMPL "INSERT INTO data (timestamp, file_id, format, header) VALUES (?, ?, ?, ?);"
-  struct evbuffer *header = NULL;
-  sqlite3_stmt *stmt = NULL;
-  unsigned char *data = NULL;
-  size_t datalen = 0;
+  sqlite3_stmt *stmt;
   int ret;
 
-  DPRINTF(E_DBG, L_CACHE, "Preparing %s header for '%s' (file id %d)\n", format, path, id);
-
-#if 1
-  if (strcmp(format, "mp4") == 0)
-    ret = transcode_prepare_header(&header, XCODE_MP4_ALAC, path);
-  else
-    ret = -1;
-
-  // Proceed even if error, we also cache that
-  if (ret == 0)
-    {
-      datalen = evbuffer_get_length(header);
-      data = evbuffer_pullup(header, -1);
-    }
-#elif
-  data = (unsigned char*)"dummy";
-  datalen = 6;
-#endif
-
   ret = sqlite3_prepare_v2(hdl, Q_TMPL, -1, &stmt, 0);
   if (ret != SQLITE_OK)
     {
-      DPRINTF(E_LOG, L_CACHE, "Error preparing xcode_data for cache update: %s\n", sqlite3_errmsg(hdl));
-      goto error;
+      DPRINTF(E_LOG, L_CACHE, "Error preparing xcode data for cache update: %s\n", sqlite3_errmsg(hdl));
+      return -1;
     }
 
   sqlite3_bind_int(stmt, 1, (uint64_t)time(NULL));
-  sqlite3_bind_int(stmt, 2, id);
+  sqlite3_bind_int(stmt, 2, file_id);
   sqlite3_bind_text(stmt, 3, format, -1, SQLITE_STATIC);
   sqlite3_bind_blob(stmt, 4, data, datalen, SQLITE_STATIC);
 
   ret = sqlite3_step(stmt);
   if (ret != SQLITE_DONE)
     {
-      DPRINTF(E_LOG, L_CACHE, "Error stepping xcode_data for cache update: %s\n", sqlite3_errmsg(hdl));
-      goto error;
+      DPRINTF(E_LOG, L_CACHE, "Error stepping xcode data for cache update: %s\n", sqlite3_errmsg(hdl));
+      return -1;
     }
 
   sqlite3_finalize(stmt);
-  if (header)
-    evbuffer_free(header);
   return 0;
-
- error:
-  if (stmt)
-    sqlite3_finalize(stmt);
-  if (header)
-    evbuffer_free(header);
-  return -1;
 #undef Q_TMPL
 }
 
 static int
-xcode_prepare_next_header_impl(sqlite3 *hdl, const char *format)
+xcode_file_next(int *file_id, char **file_path, sqlite3 *hdl, const char *format)
 {
 #define Q_TMPL "SELECT f.id, f.filepath, d.id FROM files f LEFT JOIN data d ON f.id = d.file_id AND d.format = '%q' WHERE d.id IS NULL LIMIT 1;"
   sqlite3_stmt *stmt;
-  char *query;
-  const char *file_path;
-  int file_id;
+  char query[256];
   int ret;
 
-  query = sqlite3_mprintf(Q_TMPL, format);
+  sqlite3_snprintf(sizeof(query), query, Q_TMPL, format);
 
   ret = sqlite3_prepare_v2(hdl, query, -1, &stmt, 0);
   if (ret != SQLITE_OK)
-    goto error;
+    {
+      DPRINTF(E_LOG, L_CACHE, "Error occured while finding next file to prepare header for\n");
+      return -1;
+    }
 
   ret = sqlite3_step(stmt);
   if (ret != SQLITE_ROW)
     {
       sqlite3_finalize(stmt);
-      sqlite3_free(query);
       return -1; // All done
     }
 
-  file_id = sqlite3_column_int(stmt, 0);
-  file_path = (const char *)sqlite3_column_text(stmt, 1);
-
-  xcode_prepare_header(hdl, format, file_id, file_path);
+  *file_id = sqlite3_column_int(stmt, 0);
+  *file_path = strdup((char *)sqlite3_column_text(stmt, 1));
 
   sqlite3_finalize(stmt);
-  sqlite3_free(query);
-  return file_id;
 
- error:
-  DPRINTF(E_LOG, L_CACHE, "Error occured while preparing headers\n");
-  sqlite3_free(query);
-  return -1;
+  // Save an empty header so next call to this function will return a new file
+  return xcode_header_save(hdl, *file_id, format, NULL, 0);
 #undef Q_TMPL
 }
 
+// Thread: worker
 static void
-xcode_prepare_next_header(void *arg)
+xcode_worker(void *arg)
 {
+  struct cache_xcode_job *job = *(struct cache_xcode_job **)arg;
   int ret;
 
-  // Preparing headers can take very long, so we take one at a time, letting the
-  // event loop run in between
-  ret = xcode_prepare_next_header_impl(cache_xcode_hdl, "mp4");
-  if (ret < 0 || ret == cache_xcode_last_file)
+  DPRINTF(E_DBG, L_CACHE, "Preparing %s header for '%s' (file id %d)\n", job->format, job->file_path, job->file_id);
+
+  if (strcmp(job->format, CACHE_XCODE_FORMAT_MP4) == 0)
     {
-      DPRINTF(E_LOG, L_CACHE, "Header generation completed\n");
-      cache_xcode_prepare_is_running = false;
-      return;
+      ret = transcode_prepare_header(&job->header, XCODE_MP4_ALAC, job->file_path);
+      if (ret < 0)
+	DPRINTF(E_LOG, L_CACHE, "Error preparing %s header for '%s' (file id %d)\n", job->format, job->file_path, job->file_id);
     }
 
-  // Used as failsafe to protect against infinite looping
-  cache_xcode_last_file = ret;
+  // Tell the cache thread that we are done. Only the cache thread can save the
+  // result to the DB.
+  event_active(job->ev, 0, 0);
+}
+
+static void
+cache_xcode_job_complete_cb(int fd, short what, void *arg)
+{
+  struct cache_xcode_job *job = arg;
+  uint8_t *data;
+  size_t datalen;
+
+  if (job->header)
+    {
+#if 1
+      datalen = evbuffer_get_length(job->header);
+      data = evbuffer_pullup(job->header, -1);
+#else
+      data = (unsigned char*)"dummy";
+      datalen = 6;
+#endif
+      xcode_header_save(cache_xcode_hdl, job->file_id, job->format, data, datalen);
+    }
+
+  xcode_job_clear(job); // Makes the job available again
+  event_active(cache_xcode_prepareev, 0, 0);
+}
+
+// Preparing headers can take very long, so we use worker threads. However, all
+// DB access must be from the cache thread. So this function will find the next
+// file from the db and then dispatch a thread for the encoding.
+static void
+cache_xcode_prepare_cb(int fd, short what, void *arg)
+{
+  struct cache_xcode_job *job = NULL;
+  bool is_encoding = false;
+  int ret;
+  int i;
 
   if (!cache_is_initialized)
     return;
 
-  event_active(cache_xcode_prepareev, 0, 0);
-}
+  for (i = 0; i < ARRAY_SIZE(cache_xcode_jobs); i++)
+    {
+      if (cache_xcode_jobs[i].is_encoding)
+	is_encoding = true;
+      else if (!job)
+	job = &cache_xcode_jobs[i];
+    }
 
-static void
-cache_xcode_prepare_cb(int fd, short what, void *arg)
-{
-  worker_execute(xcode_prepare_next_header, NULL, 0, 0);
+  if (!job)
+    return; // No available thread right now, wait for cache_xcode_job_complete_cb()
+
+  ret = xcode_file_next(&job->file_id, &job->file_path, cache_xcode_hdl, CACHE_XCODE_FORMAT_MP4);
+  if (ret < 0)
+    {
+      if (!is_encoding)
+	DPRINTF(E_LOG, L_CACHE, "Header generation completed\n");
+
+      return;
+    }
+  else if (!is_encoding)
+    DPRINTF(E_LOG, L_CACHE, "Kicking off header generation\n");
+
+  job->is_encoding = true;
+  job->format = CACHE_XCODE_FORMAT_MP4;
+
+  worker_execute(xcode_worker, &job, sizeof(struct cache_xcode_job *), 0);
+
+  // Set off more threads
+  event_active(cache_xcode_prepareev, 0, 0);
 }
 
 static void
@@ -1218,12 +1281,6 @@ cache_xcode_update_cb(int fd, short what, void *arg)
   if (xcode_sync_with_files(cache_xcode_hdl) < 0)
     return;
 
-  if (!cache_is_initialized || cache_xcode_prepare_is_running)
-    return;
-
-  DPRINTF(E_LOG, L_CACHE, "Kicking off header generation\n");
-
-  cache_xcode_prepare_is_running = true;
   event_active(cache_xcode_prepareev, 0, 0);
 }
 
@@ -1628,6 +1685,7 @@ static void *
 cache(void *arg)
 {
   int ret;
+  int i;
 
   ret = cache_open();
   if (ret < 0)
@@ -1651,6 +1709,8 @@ cache(void *arg)
   CHECK_NULL(L_CACHE, cache_xcode_updateev = evtimer_new(evbase_cache, cache_xcode_update_cb, NULL));
   CHECK_NULL(L_CACHE, cache_xcode_prepareev = evtimer_new(evbase_cache, cache_xcode_prepare_cb, NULL));
   CHECK_ERR(L_CACHE, event_priority_set(cache_xcode_prepareev, 0));
+  for (i = 0; i < ARRAY_SIZE(cache_xcode_jobs); i++)
+    CHECK_NULL(L_CACHE, cache_xcode_jobs[i].ev = evtimer_new(evbase_cache, cache_xcode_job_complete_cb, &cache_xcode_jobs[i]));
 
   CHECK_ERR(L_CACHE, listener_add(cache_daap_listener_cb, LISTENER_DATABASE));
 
@@ -1666,6 +1726,8 @@ cache(void *arg)
 
   listener_remove(cache_daap_listener_cb);
 
+  for (i = 0; i < ARRAY_SIZE(cache_xcode_jobs); i++)
+    event_free(cache_xcode_jobs[i].ev);
   event_free(cache_xcode_prepareev);
   event_free(cache_xcode_updateev);
   event_free(cache_daap_updateev);