ffmpeg: use AV_BUFFERSRC_FLAG_PUSH.

It reduces the lifespan of buffers in filter graphs,
and therefore the memory consumption.

ffmpeg.c

@@ -193,7 +193,8 @@ static void sub2video_push_ref(InputStream *ist, int64_t pts)
         av_buffersrc_add_ref(ist->filters[i]->filter,
                              avfilter_ref_buffer(ref, ~0),
                              AV_BUFFERSRC_FLAG_NO_CHECK_FORMAT |
-                             AV_BUFFERSRC_FLAG_NO_COPY);
+                             AV_BUFFERSRC_FLAG_NO_COPY |
+                             AV_BUFFERSRC_FLAG_PUSH);
 }
 
 static void sub2video_update(InputStream *ist, AVSubtitle *sub, int64_t pts)
@@ -1508,7 +1509,8 @@ static int decode_audio(InputStream *ist, AVPacket *pkt, int *got_output)
                                           decoded_frame_tb,
                                           (AVRational){1, ist->st->codec->sample_rate});
     for (i = 0; i < ist->nb_filters; i++)
-        av_buffersrc_add_frame(ist->filters[i]->filter, decoded_frame, 0);
+        av_buffersrc_add_frame(ist->filters[i]->filter, decoded_frame,
+                               AV_BUFFERSRC_FLAG_PUSH);
 
     decoded_frame->pts = AV_NOPTS_VALUE;
 
@@ -1619,9 +1621,10 @@ static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output)
             buf->refcount++;
             av_buffersrc_add_ref(ist->filters[i]->filter, fb,
                                  AV_BUFFERSRC_FLAG_NO_CHECK_FORMAT |
-                                 AV_BUFFERSRC_FLAG_NO_COPY);
+                                 AV_BUFFERSRC_FLAG_NO_COPY |
+                                 AV_BUFFERSRC_FLAG_PUSH);
         } else
-        if(av_buffersrc_add_frame(ist->filters[i]->filter, decoded_frame, 0)<0) {
+        if(av_buffersrc_add_frame(ist->filters[i]->filter, decoded_frame, AV_BUFFERSRC_FLAG_PUSH)<0) {
             av_log(NULL, AV_LOG_FATAL, "Failed to inject frame into filter network\n");
             exit_program(1);
         }