buffersink: add AV_BUFFERSINK_FLAG_NO_REQUEST.

libavfilter/buffersink.h

@@ -63,6 +63,13 @@ AVABufferSinkParams *av_abuffersink_params_alloc(void);
  */
 #define AV_BUFFERSINK_FLAG_PEEK 1
 
+/**
+ * Tell av_buffersink_get_buffer_ref() not to request a frame fom its input.
+ * If a frame is already buffered, it is read (and removed from the buffer),
+ * but if no frame is present, return AVERROR(EAGAIN).
+ */
+#define AV_BUFFERSINK_FLAG_NO_REQUEST 2
+
 /**
  * Get an audio/video buffer data from buffer_sink and put it in bufref.
  *

libavfilter/sink_buffer.c

@@ -126,6 +126,8 @@ int av_buffersink_get_buffer_ref(AVFilterContext *ctx,
 
     /* no picref available, fetch it from the filterchain */
     if (!av_fifo_size(buf->fifo)) {
+        if (flags & AV_BUFFERSINK_FLAG_NO_REQUEST)
+            return AVERROR(EAGAIN);
         if ((ret = avfilter_request_frame(inlink)) < 0)
             return ret;
     }

libavfilter/version.h

@@ -29,8 +29,8 @@
 #include "libavutil/avutil.h"
 
 #define LIBAVFILTER_VERSION_MAJOR  2
-#define LIBAVFILTER_VERSION_MINOR 71
-#define LIBAVFILTER_VERSION_MICRO 102
+#define LIBAVFILTER_VERSION_MINOR 72
+#define LIBAVFILTER_VERSION_MICRO 100
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \