diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index f054f7a405..a2af7e9f89 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -553,9 +553,21 @@ typedef struct AVOutputFormat {
     /**
      * A format-specific function for interleavement.
      * If unset, packets will be interleaved by dts.
-     */
-    int (*interleave_packet)(struct AVFormatContext *, AVPacket *out,
-                             AVPacket *in, int flush);
+     *
+     * @param s           An AVFormatContext for output. pkt will be added to
+     *                    resp. taken from its packet buffer.
+     * @param[in,out] pkt A packet to be interleaved if has_packet is set;
+     *                    also used to return packets. If no packet is returned
+     *                    (e.g. on error), pkt is blank on return.
+     * @param flush       1 if no further packets are available as input and
+     *                    all remaining packets should be output.
+     * @param has_packet  If set, pkt contains a packet to be interleaved
+     *                    on input; otherwise pkt is blank on input.
+     * @return 1 if a packet was output, 0 if no packet could be output,
+     *         < 0 if an error occurred
+     */
+    int (*interleave_packet)(struct AVFormatContext *s, AVPacket *pkt,
+                             int flush, int has_packet);
     /**
      * Test if the given codec can be stored in this container.
      *
diff --git a/libavformat/gxfenc.c b/libavformat/gxfenc.c
index 8cc3bd456e..133d1e9fb3 100644
--- a/libavformat/gxfenc.c
+++ b/libavformat/gxfenc.c
@@ -992,10 +992,11 @@ static int gxf_compare_field_nb(AVFormatContext *s, const AVPacket *next,
         (field_nb[1] == field_nb[0] && sc[1]->order > sc[0]->order);
 }
 
-static int gxf_interleave_packet(AVFormatContext *s, AVPacket *out, AVPacket *pkt, int flush)
+static int gxf_interleave_packet(AVFormatContext *s, AVPacket *pkt,
+                                 int flush, int has_packet)
 {
     int ret;
-    if (pkt) {
+    if (has_packet) {
         AVStream *st = s->streams[pkt->stream_index];
         GXFStreamContext *sc = st->priv_data;
         if (st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)
@@ -1006,7 +1007,7 @@ static int gxf_interleave_packet(AVFormatContext *s, AVPacket *out, AVPacket *pk
         if ((ret = ff_interleave_add_packet(s, pkt, gxf_compare_field_nb)) < 0)
             return ret;
     }
-    return ff_interleave_packet_per_dts(s, out, NULL, flush);
+    return ff_interleave_packet_per_dts(s, pkt, flush, 0);
 }
 
 const AVOutputFormat ff_gxf_muxer = {
diff --git a/libavformat/internal.h b/libavformat/internal.h
index 6f1f1c072a..98341ba217 100644
--- a/libavformat/internal.h
+++ b/libavformat/internal.h
@@ -107,7 +107,8 @@ typedef struct FFFormatContext {
     struct PacketList *parse_queue_end;
     /**
      * The generic code uses this as a temporary packet
-     * to parse packets; it may also be used for other means
+     * to parse packets or for muxing, especially flushing.
+     * For demuxers, it may also be used for other means
      * for short periods that are guaranteed not to overlap
      * with calls to av_read_frame() (or ff_read_packet())
      * or with each other.
@@ -746,18 +747,10 @@ int ff_add_attached_pic(AVFormatContext *s, AVStream *st, AVIOContext *pb,
 
 /**
  * Interleave an AVPacket per dts so it can be muxed.
- *
- * @param s   an AVFormatContext for output. pkt resp. out will be added to
- *            resp. taken from its packet buffer.
- * @param out the interleaved packet will be output here
- * @param pkt the input packet; will be blank on return if not NULL
- * @param flush 1 if no further packets are available as input and all
- *              remaining packets should be output
- * @return 1 if a packet was output, 0 if no packet could be output
- *         (in which case out may be uninitialized), < 0 if an error occurred
- */
-int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
-                                 AVPacket *pkt, int flush);
+ * See the documentation of AVOutputFormat.interleave_packet for details.
+ */
+int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *pkt,
+                                 int flush, int has_packet);
 
 void ff_free_stream(AVFormatContext *s, AVStream *st);
 
diff --git a/libavformat/mux.c b/libavformat/mux.c
index d7b2bdb4b3..d924bb08fc 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -903,8 +903,8 @@ static int interleave_compare_dts(AVFormatContext *s, const AVPacket *next,
     return comp > 0;
 }
 
-int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
-                                 AVPacket *pkt, int flush)
+int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *pkt,
+                                 int flush, int has_packet)
 {
     FFFormatContext *const si = ffformatcontext(s);
     int stream_count = 0;
@@ -912,7 +912,7 @@ int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
     int ret;
     int eof = flush;
 
-    if (pkt) {
+    if (has_packet) {
         if ((ret = ff_interleave_add_packet(s, pkt, interleave_compare_dts)) < 0)
             return ret;
     }
@@ -1009,7 +1009,7 @@ int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
         AVStream *const st = s->streams[pktl->pkt.stream_index];
         FFStream *const sti = ffstream(st);
 
-        *out = pktl->pkt;
+        *pkt = pktl->pkt;
 
         si->packet_buffer = pktl->next;
         if (!si->packet_buffer)
@@ -1055,20 +1055,16 @@ const AVPacket *ff_interleaved_peek(AVFormatContext *s, int stream)
 }
 
 /**
- * Interleave an AVPacket correctly so it can be muxed.
- * @param out the interleaved packet will be output here
- * @param in the input packet; will always be blank on return if not NULL
- * @param flush 1 if no further packets are available as input and all
- *              remaining packets should be output
- * @return 1 if a packet was output, 0 if no packet could be output,
- *         < 0 if an error occurred
+ * A wrapper around AVOutputFormat.interleave_packet.
+ * See its documentation for details.
  */
-static int interleave_packet(AVFormatContext *s, AVPacket *out, AVPacket *in, int flush)
+static int interleave_packet(AVFormatContext *s, AVPacket *pkt,
+                             int flush, int has_packet)
 {
     if (s->oformat->interleave_packet) {
-        return s->oformat->interleave_packet(s, out, in, flush);
+        return s->oformat->interleave_packet(s, pkt, flush, has_packet);
     } else
-        return ff_interleave_packet_per_dts(s, out, in, flush);
+        return ff_interleave_packet_per_dts(s, pkt, flush, has_packet);
 }
 
 static int check_bitstream(AVFormatContext *s, FFStream *sti, AVPacket *pkt)
@@ -1090,20 +1086,18 @@ static int check_bitstream(AVFormatContext *s, FFStream *sti, AVPacket *pkt)
     return 1;
 }
 
-static int interleaved_write_packet(AVFormatContext *s, AVPacket *pkt, int flush)
+static int interleaved_write_packet(AVFormatContext *s, AVPacket *pkt,
+                                    int flush, int has_packet)
 {
     for (;; ) {
-        AVPacket opkt;
-        int ret = interleave_packet(s, &opkt, pkt, flush);
+        int ret = interleave_packet(s, pkt, flush, has_packet);
         if (ret <= 0)
             return ret;
 
-        pkt = NULL;
-
-        ret = write_packet(s, &opkt);
-
-        av_packet_unref(&opkt);
+        has_packet = 0;
 
+        ret = write_packet(s, pkt);
+        av_packet_unref(pkt);
         if (ret < 0)
             return ret;
     }
@@ -1127,7 +1121,7 @@ static int write_packet_common(AVFormatContext *s, AVStream *st, AVPacket *pkt,
     if (interleaved) {
         if (pkt->dts == AV_NOPTS_VALUE && !(s->oformat->flags & AVFMT_NOTIMESTAMPS))
             return AVERROR(EINVAL);
-        return interleaved_write_packet(s, pkt, 0);
+        return interleaved_write_packet(s, pkt, 0, 1);
     } else {
         return write_packet(s, pkt);
     }
@@ -1251,7 +1245,7 @@ int av_interleaved_write_frame(AVFormatContext *s, AVPacket *pkt)
         return ret;
     } else {
         av_log(s, AV_LOG_TRACE, "av_interleaved_write_frame FLUSH\n");
-        return interleaved_write_packet(s, NULL, 1/*flush*/);
+        return interleaved_write_packet(s, ffformatcontext(s)->parse_pkt, 1/*flush*/, 0);
     }
 }
 
@@ -1271,7 +1265,7 @@ int av_write_trailer(AVFormatContext *s)
                 ret = ret1;
         }
     }
-    ret1 = interleaved_write_packet(s, NULL, 1);
+    ret1 = interleaved_write_packet(s, pkt, 1, 0);
     if (ret >= 0)
         ret = ret1;
 
diff --git a/libavformat/mxfenc.c b/libavformat/mxfenc.c
index 56facbe4b7..c36ebef932 100644
--- a/libavformat/mxfenc.c
+++ b/libavformat/mxfenc.c
@@ -3096,7 +3096,7 @@ static void mxf_deinit(AVFormatContext *s)
     }
 }
 
-static int mxf_interleave_get_packet(AVFormatContext *s, AVPacket *out, AVPacket *pkt, int flush)
+static int mxf_interleave_get_packet(AVFormatContext *s, AVPacket *out, int flush)
 {
     FFFormatContext *const si = ffformatcontext(s);
     int i, stream_count = 0;
@@ -3161,16 +3161,17 @@ static int mxf_compare_timestamps(AVFormatContext *s, const AVPacket *next,
         (next->dts == pkt->dts && sc->order < sc2->order);
 }
 
-static int mxf_interleave(AVFormatContext *s, AVPacket *out, AVPacket *pkt, int flush)
+static int mxf_interleave(AVFormatContext *s, AVPacket *pkt,
+                          int flush, int has_packet)
 {
     int ret;
-    if (pkt) {
+    if (has_packet) {
         MXFStreamContext *sc = s->streams[pkt->stream_index]->priv_data;
         pkt->pts = pkt->dts = sc->pkt_cnt++;
         if ((ret = ff_interleave_add_packet(s, pkt, mxf_compare_timestamps)) < 0)
             return ret;
     }
-    return mxf_interleave_get_packet(s, out, NULL, flush);
+    return mxf_interleave_get_packet(s, pkt, flush);
 }
 
 #define MXF_COMMON_OPTIONS \