@@ -323,6 +323,10 @@ int ff_request_frame(AVFilterLink *link)

     if (link->closed)

         return AVERROR_EOF;

+    av_assert0(!link->frame_requested);

+    link->frame_requested = 1;

+    while (link->frame_requested) {

+        /* TODO reindent */

     if (link->srcpad->request_frame)

         ret = link->srcpad->request_frame(link);

     else if (link->src->inputs[0])

@@ -332,8 +336,15 @@ int ff_request_frame(AVFilterLink *link)

         link->partial_buf = NULL;

         ret = ff_filter_frame_framed(link, pbuf);

     }

-    if (ret == AVERROR_EOF)

-        link->closed = 1;

+        if (ret < 0) {

+            link->frame_requested = 0;

+            if (ret == AVERROR_EOF)

+                link->closed = 1;

+        } else {

+            av_assert0(!link->frame_requested ||

+                       link->flags & FF_LINK_FLAG_REQUEST_LOOP);

+        }

+    }

     return ret;

 }

@@ -702,6 +713,7 @@ static int ff_filter_frame_framed(AVFilterLink *link, AVFrame *frame)

     pts = out->pts;

     ret = filter_frame(link, out);

+    link->frame_requested = 0;

     ff_update_link_current_pts(link, pts);

     return ret;

 }

@@ -713,6 +725,7 @@ static int ff_filter_frame_needs_framing(AVFilterLink *link, AVFrame *frame)

     int nb_channels = av_frame_get_channels(frame);

     int ret = 0;

+    link->flags |= FF_LINK_FLAG_REQUEST_LOOP;

     /* Handle framing (min_samples, max_samples) */

     while (insamples) {

         if (!pbuf) {

@@ -682,6 +682,17 @@ struct AVFilterLink {

      * Number of channels.

      */

     int channels;

+

+    /**

+     * True if a frame is being requested on the link.

+     * Used internally by the framework.

+     */

+    unsigned frame_requested;

+

+    /**

+     * Link processing flags.

+     */

+    unsigned flags;

 };

 /**

@@ -325,4 +325,18 @@ int ff_buffersink_read_samples_compat(AVFilterContext *ctx, AVFilterBufferRef **

  */

 int ff_filter_frame(AVFilterLink *link, AVFrame *frame);

+/**

+ * Flags for AVFilterLink.flags.

+ */

+enum {

+

+    /**

+     * Frame requests may need to loop in order to be fulfilled.

+     * A filter must set this flags on an output link if it may return 0 in

+     * request_frame() without filtering a frame.

+     */

+    FF_LINK_FLAG_REQUEST_LOOP = 1,

+

+};

+

 #endif /* AVFILTER_INTERNAL_H */