make av_interleaved_write_frame() flush packets when pkt is NULL

This patch allows the user to force flushing of all queued packets
by calling av_interleaved_write_frame() with pkt set to NULL.
Signed-off-by: Jindrich Makovicka <jindrich.makovicka@nangu.tv>
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/avformat.h

@@ -1436,6 +1436,8 @@ int av_write_frame(AVFormatContext *s, AVPacket *pkt);
  * @param s media file handle
  * @param pkt The packet containing the data to be written. Libavformat takes
  * ownership of the data and will free it when it sees fit using the packet's
+ * This can be NULL (at any time, not just at the end), to flush the
+ * interleaving queues.
  * @ref AVPacket.destruct "destruct" field. The caller must not access the data
  * after this function returns, as it may already be freed.
  * Packet's @ref AVPacket.stream_index "stream_index" field must be set to the

libavformat/utils.c

@@ -3128,8 +3128,10 @@ static int interleave_packet(AVFormatContext *s, AVPacket *out, AVPacket *in, in
 }
 
 int av_interleaved_write_frame(AVFormatContext *s, AVPacket *pkt){
+    int ret, flush = 0;
+
+    if (pkt) {
         AVStream *st= s->streams[ pkt->stream_index];
-    int ret;
 
         //FIXME/XXX/HACK drop zero sized packets
         if(st->codec->codec_type == AVMEDIA_TYPE_AUDIO && pkt->size==0)
@@ -3142,10 +3144,14 @@ int av_interleaved_write_frame(AVFormatContext *s, AVPacket *pkt){
 
         if(pkt->dts == AV_NOPTS_VALUE && !(s->oformat->flags & AVFMT_NOTIMESTAMPS))
             return AVERROR(EINVAL);
+    } else {
+        av_dlog(s, "av_interleaved_write_frame FLUSH\n");
+        flush = 1;
+    }
 
     for(;;){
         AVPacket opkt;
-        int ret= interleave_packet(s, &opkt, pkt, 0);
+        int ret= interleave_packet(s, &opkt, pkt, flush);
         if(ret<=0) //FIXME cleanup needed for ret<0 ?
             return ret;