fftools: use av_dict_get_string

Instead of manually assembling the string, use av_dict_get_string
which handles things like proper escaping too (even though it is
not yet needed here).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

fftools/ffmpeg_filter.c

@@ -972,39 +972,34 @@ int configure_filtergraph(FilterGraph *fg)
 
     if (simple) {
         OutputStream *ost = fg->outputs[0]->ost;
-        char args[512];
-        const AVDictionaryEntry *e = NULL;
 
         if (filter_nbthreads) {
             ret = av_opt_set(fg->graph, "threads", filter_nbthreads, 0);
             if (ret < 0)
                 goto fail;
         } else {
+            const AVDictionaryEntry *e = NULL;
             e = av_dict_get(ost->encoder_opts, "threads", NULL, 0);
             if (e)
                 av_opt_set(fg->graph, "threads", e->value, 0);
         }
 
-        args[0] = 0;
-        e       = NULL;
-        while ((e = av_dict_get(ost->sws_dict, "", e,
-                                AV_DICT_IGNORE_SUFFIX))) {
-            av_strlcatf(args, sizeof(args), "%s=%s:", e->key, e->value);
-        }
-        if (strlen(args)) {
-            args[strlen(args)-1] = 0;
-            fg->graph->scale_sws_opts = av_strdup(args);
+        if (av_dict_count(ost->sws_dict)) {
+            ret = av_dict_get_string(ost->sws_dict,
+                                     &fg->graph->scale_sws_opts,
+                                     '=', ':');
+            if (ret < 0)
+                goto fail;
         }
 
-        args[0] = 0;
-        e       = NULL;
-        while ((e = av_dict_get(ost->swr_opts, "", e,
-                                AV_DICT_IGNORE_SUFFIX))) {
-            av_strlcatf(args, sizeof(args), "%s=%s:", e->key, e->value);
+        if (av_dict_count(ost->swr_opts)) {
+            char *args;
+            ret = av_dict_get_string(ost->swr_opts, &args, '=', ':');
+            if (ret < 0)
+                goto fail;
+            av_opt_set(fg->graph, "aresample_swr_opts", args, 0);
+            av_free(args);
         }
-        if (strlen(args))
-            args[strlen(args)-1] = 0;
-        av_opt_set(fg->graph, "aresample_swr_opts", args, 0);
     } else {
         fg->graph->nb_threads = filter_complex_nbthreads;
     }