fecdec: Defer decoding until the first slice of the second group arrives.

Otherwise, this could lead to buffer underruns in the decoding application
in case slices are missed. So introdce group_completion_status which tracks
whether we already have received the first group sucessfully and are waiting
for the first slice of the next group.

diff --git a/fecdec_filter.c b/fecdec_filter.c
index a3cba9bbd0b3821b545a3aed6a7bb8606ec97b95..74e1b4f58ba7f93caedeae5c1097b78740d4d71e 100644 (file)
--- a/fecdec_filter.c
+++ b/fecdec_filter.c
@@ -4,7 +4,7 @@
  * Licensed under the GPL v2. For licencing details see COPYING.
  */
 
-/** \file fecdec_filter.c A filter fec-decodes an audio stream. */
+/** \file fecdec_filter.c A filter that fec-decodes an audio stream. */
 
 #include <dirent.h>
 #include "para.h"
@@ -70,6 +70,20 @@ struct fecdec_group {
        unsigned char **data;
 };
 
+/**
+ * The fecdec filter defers decoding of the first group until the first slice
+ * of the next group was received. This avoids buffer underruns in subsequent
+ * filters of the filter chain.
+ */
+enum group_completion_status {
+       /** No complete group received so far. */
+       GCS_NO_COMPLETE_GROUP,
+       /** First group received, but not yet decoded. */
+       GCS_FIRST_GROUP_COMPLETE,
+       /** At least one complete group decoded. */
+       GCS_FIRST_GROUP_DECODED,
+};
+
 /**
  * Data private to the fecdec filter.
  */
@@ -80,6 +94,10 @@ struct private_fecdec_data {
        struct fecdec_group groups[NUM_FEC_GROUPS];
        /** Whether an audio file header was already received. */
        int have_header;
+       /** See \ref group_completion_status. */
+       unsigned completion_status;
+       /** Points to the first received group. */
+       struct fecdec_group *first_complete_group;
 };
 
 /** Iterate over all fecdec groups. */
@@ -153,6 +171,13 @@ static struct fecdec_group *try_to_free_group(struct private_fecdec_data *pfd)
        FOR_EACH_FECDEC_GROUP(fg, pfd) {
                if (!group_complete(fg))
                        continue;
+               /*
+                * Don't clear the first complete group if it has not yet been
+                * decoded.
+                */
+               if (pfd->completion_status == GCS_FIRST_GROUP_COMPLETE
+                               && pfd->first_complete_group == fg)
+                       continue;
                clear_group(fg);
                return fg;
        }
@@ -171,6 +196,8 @@ static struct fecdec_group *free_oldest_group(struct private_fecdec_data *pfd)
                PARA_WARNING_LOG("Clearing incomplete group %d "
                        "(contains %d slices)\n", oldest->h.group_num,
                        oldest->num_received_slices);
+       assert(pfd->completion_status != GCS_FIRST_GROUP_COMPLETE
+               || oldest != pfd->first_complete_group);
        clear_group(oldest);
        return oldest;
 }
@@ -211,8 +238,8 @@ static int add_slice(char *buf, struct fecdec_group *fg)
        int r, slice_num;
 
        if (group_complete(fg)) {
-               PARA_DEBUG_LOG("group complete, ignoring slice %d\n",
-                       fg->h.slice_num);
+               PARA_DEBUG_LOG("group %d complete, ignoring slice %d\n",
+                       fg->h.group_num, fg->h.slice_num);
                fg->num_received_slices++;
                return 0;
        }
@@ -267,7 +294,7 @@ static int decode_group(struct fecdec_group *fg, struct filter_node *fn)
                PARA_INFO_LOG("dropping unusable group %d\n", fg->h.group_num);
                return 0;
        }
-       PARA_DEBUG_LOG("decoding group %d %d slices\n", fg->h.group_num,
+       PARA_DEBUG_LOG("decoding group %d (%d slices)\n", fg->h.group_num,
                fg->h.data_slices_per_group);
        ret = fec_decode(pfd->fec, fg->data, fg->idx, sb);
        if (ret < 0)
@@ -339,7 +366,7 @@ static int dispatch_slice(char *buf, size_t len, struct fec_header *h,
                struct filter_node *fn)
 {
        struct fecdec_group *fg;
-       int ret;
+       int ret, k, n;
        struct private_fecdec_data *pfd = fn->private_data;
 
        if (h->slice_bytes > len) /* can not use the thing, try to read more */
@@ -350,17 +377,34 @@ static int dispatch_slice(char *buf, size_t len, struct fec_header *h,
        if (!add_slice(buf, fg))
                return 1;
        if (group_complete(fg)) {
-               if (!pfd->fec) {
-                       int k = h->data_slices_per_group, n = h->slices_per_group;
-                       PARA_NOTICE_LOG("init fec (%d, %d)\n", k, n);
-                       ret = fec_new(k, n, &pfd->fec);
-                       if (ret < 0)
-                               return ret;
+               if (pfd->completion_status == GCS_NO_COMPLETE_GROUP) {
+                       pfd->completion_status = GCS_FIRST_GROUP_COMPLETE;
+                       pfd->first_complete_group = fg;
+                       return 1;
                }
+               assert(pfd->fec);
                ret = decode_group(fg, fn);
                if (ret < 0)
                        return ret;
+               return 1;
        }
+       if (pfd->completion_status == GCS_NO_COMPLETE_GROUP)
+               return 1;
+       if (pfd->completion_status == GCS_FIRST_GROUP_DECODED)
+               return 1;
+       if (fg == pfd->first_complete_group)
+               return 1;
+       assert(!pfd->fec);
+       k = h->data_slices_per_group;
+       n = h->slices_per_group;
+       PARA_NOTICE_LOG("init fec (%d, %d)\n", k, n);
+       ret = fec_new(k, n, &pfd->fec);
+       if (ret < 0)
+               return ret;
+       ret = decode_group(pfd->first_complete_group, fn);
+       if (ret < 0)
+               return ret;
+       pfd->completion_status = GCS_FIRST_GROUP_DECODED;
        return 1;
 }
 
@@ -400,9 +444,12 @@ static void fecdec_close(struct filter_node *fn)
 
 static void fecdec_open(struct filter_node *fn)
 {
+       struct private_fecdec_data *pfd;
        fn->bufsize = FECDEC_DEFAULT_OUTBUF_SIZE;
        fn->buf = para_malloc(fn->bufsize);
-       fn->private_data = para_calloc(sizeof(struct private_fecdec_data));
+       pfd = para_calloc(sizeof(*pfd));
+       pfd->completion_status = GCS_NO_COMPLETE_GROUP;
+       fn->private_data = pfd;
        fn->loaded = 0;
 }