fftools/ffmpeg_filter: restrict reap_filters() to a single filtergraph

This is more natural, as all except one of its callers require
processing only one filtergraph.

fftools/ffmpeg.c

@@ -1171,7 +1171,15 @@ static int transcode_step(OutputStream *ost)
     if (ret < 0)
         return ret == AVERROR_EOF ? 0 : ret;
 
-    return reap_filters(0);
+    // process_input() above might have caused output to become available
+    // in multiple filtergraphs, so we process all of them
+    for (int i = 0; i < nb_filtergraphs; i++) {
+        ret = reap_filters(filtergraphs[i], 0);
+        if (ret < 0)
+            return ret;
+    }
+
+    return 0;
 }
 
 /*

fftools/ffmpeg.h

@@ -765,12 +765,12 @@ void fg_free(FilterGraph **pfg);
 int fg_transcode_step(FilterGraph *graph, InputStream **best_ist);
 
 /**
- * Get and encode new output from any of the filtergraphs, without causing
+ * Get and encode new output from specified filtergraph, without causing
  * activity.
  *
  * @return  0 for success, <0 for severe errors
  */
-int reap_filters(int flush);
+int reap_filters(FilterGraph *fg, int flush);
 
 int ffmpeg_parse_options(int argc, char **argv);
 

fftools/ffmpeg_filter.c

@@ -1695,24 +1695,23 @@ int filtergraph_is_simple(const FilterGraph *fg)
     return fgp->is_simple;
 }
 
-int reap_filters(int flush)
+int reap_filters(FilterGraph *fg, int flush)
 {
+    FilterGraphPriv    *fgp = fgp_from_fg(fg);
+    AVFrame *filtered_frame = fgp->frame;
+
+    if (!fg->graph)
+        return 0;
+
     /* Reap all buffers present in the buffer sinks */
-    for (OutputStream *ost = ost_iter(NULL); ost; ost = ost_iter(ost)) {
-        OutputFilterPriv *ofp;
-        FilterGraphPriv *fgp;
-        AVFrame *filtered_frame;
-        AVFilterContext *filter;
+    for (int i = 0; i < fg->nb_outputs; i++) {
+        OutputFilter   *ofilter = fg->outputs[i];
+        OutputStream       *ost = ofilter->ost;
+        OutputFilterPriv   *ofp = ofp_from_ofilter(ofilter);
+        AVFilterContext *filter = ofp->filter;
+
         int ret = 0;
 
-        if (!ost->filter || !ost->filter->graph->graph)
-            continue;
-        fgp    = fgp_from_fg(ost->filter->graph);
-        ofp    = ofp_from_ofilter(ost->filter);
-        filter = ofp->filter;
-
-        filtered_frame = fgp->frame;
-
         while (1) {
             FrameData *fd;
 
@@ -1931,7 +1930,7 @@ int ifilter_send_frame(InputFilter *ifilter, AVFrame *frame, int keep_reference)
             return ret;
         }
 
-        ret = reap_filters(0);
+        ret = reap_filters(fg, 0);
         if (ret < 0 && ret != AVERROR_EOF) {
             av_log(fg, AV_LOG_ERROR, "Error while filtering: %s\n", av_err2str(ret));
             return ret;
@@ -2000,10 +1999,10 @@ int fg_transcode_step(FilterGraph *graph, InputStream **best_ist)
     *best_ist = NULL;
     ret = avfilter_graph_request_oldest(graph->graph);
     if (ret >= 0)
-        return reap_filters(0);
+        return reap_filters(graph, 0);
 
     if (ret == AVERROR_EOF) {
-        reap_filters(1);
+        reap_filters(graph, 1);
         for (int i = 0; i < graph->nb_outputs; i++) {
             OutputFilter *ofilter = graph->outputs[i];
             OutputFilterPriv *ofp = ofp_from_ofilter(ofilter);