fftools/ffmpeg: add support for setting maximum buffered frames in a filtergraph

Signed-off-by: Marton Balint <cus@passwd.hu>

doc/ffmpeg.texi

@@ -1384,6 +1384,15 @@ Defines how many threads are used to process a filter pipeline. Each pipeline
 will produce a thread pool with this many threads available for parallel processing.
 The default is the number of available CPUs.
 
+@item -filter_buffered_frames @var{nb_frames} (@emph{global})
+Defines the maximum number of buffered frames allowed in a filtergraph. Under
+normal circumstances, a filtergraph should not buffer more than a few frames,
+especially if frames are being fed to it and read from it in a balanced way
+(which is the intended behavior in ffmpeg). That said, this option allows you
+to limit the total number of frames buffered across all links in a filtergraph.
+If more frames are generated, filtering is aborted and an error is returned.
+The default value is 0, which means no limit.
+
 @item -pre[:@var{stream_specifier}] @var{preset_name} (@emph{output,per-stream})
 Specify the preset for matching stream(s).
 

fftools/ffmpeg.h

@@ -737,6 +737,7 @@ extern float max_error_rate;
 
 extern char *filter_nbthreads;
 extern int filter_complex_nbthreads;
+extern int filter_buffered_frames;
 extern int vstats_version;
 extern int print_graphs;
 extern char *print_graphs_file;

fftools/ffmpeg_filter.c

@@ -1949,6 +1949,12 @@ static int configure_filtergraph(FilterGraph *fg, FilterGraphThread *fgt)
         fgt->graph->nb_threads = filter_complex_nbthreads;
     }
 
+    if (filter_buffered_frames) {
+        ret = av_opt_set_int(fgt->graph, "max_buffered_frames", filter_buffered_frames, 0);
+        if (ret < 0)
+            return ret;
+    }
+
     hw_device = hw_device_for_filter();
 
     ret = graph_parse(fg, fgt->graph, graph_desc, &inputs, &outputs, hw_device);

fftools/ffmpeg_opt.c

@@ -75,6 +75,7 @@ int stdin_interaction = 1;
 float max_error_rate  = 2.0/3;
 char *filter_nbthreads;
 int filter_complex_nbthreads = 0;
+int filter_buffered_frames = 0;
 int vstats_version = 2;
 int print_graphs = 0;
 char *print_graphs_file = NULL;
@@ -1714,6 +1715,9 @@ const OptionDef options[] = {
     { "filter_threads",         OPT_TYPE_FUNC, OPT_FUNC_ARG | OPT_EXPERT,
         { .func_arg = opt_filter_threads },
         "number of non-complex filter threads" },
+    { "filter_buffered_frames", OPT_TYPE_INT, OPT_EXPERT,
+        { &filter_buffered_frames },
+        "maximum number of buffered frames in a filter graph" },
 #if FFMPEG_OPT_FILTER_SCRIPT
     { "filter_script",          OPT_TYPE_STRING, OPT_PERSTREAM | OPT_EXPERT | OPT_OUTPUT,
         { .off = OFFSET(filter_scripts) },