diff --git a/libavformat/avformat.h b/libavformat/avformat.h
index f66c39b1c1..4eb11404ca 100644
--- a/libavformat/avformat.h
+++ b/libavformat/avformat.h
@@ -2427,6 +2427,10 @@ int av_write_frame(AVFormatContext *s, AVPacket *pkt);
  * increasing dts. Callers doing their own interleaving should call
  * av_write_frame() instead of this function.
  *
+ * Using this function instead of av_write_frame() can give muxers advance
+ * knowledge of future packets, improving e.g. the behaviour of the mp4
+ * muxer for VFR content in fragmenting mode.
+ *
  * @param s media file handle
  * @param pkt The packet containing the data to be written.
  *            <br>
diff --git a/libavformat/internal.h b/libavformat/internal.h
index 99015271b6..6b7f677950 100644
--- a/libavformat/internal.h
+++ b/libavformat/internal.h
@@ -620,4 +620,14 @@ int ff_get_packet_palette(AVFormatContext *s, AVPacket *pkt, int ret, uint32_t *
  */
 int ff_bprint_to_codecpar_extradata(AVCodecParameters *par, struct AVBPrint *buf);
 
+/**
+ * Find the next packet in the interleaving queue for the given stream.
+ * The packet is not removed from the interleaving queue, but only
+ * a pointer to it is returned.
+ *
+ * @return a pointer to the next packet, or NULL if no packet is queued
+ *         for this stream.
+ */
+const AVPacket *ff_interleaved_peek(AVFormatContext *s, int stream);
+
 #endif /* AVFORMAT_INTERNAL_H */
diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 4e5f65f24b..0a7983658e 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -4241,6 +4241,25 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
     if (!(mov->flags & FF_MOV_FLAG_FRAGMENT))
         return 0;
 
+    // Try to fill in the duration of the last packet in each stream
+    // from queued packets in the interleave queues. If the flushing
+    // of fragments was triggered automatically by an AVPacket, we
+    // already have reliable info for the end of that track, but other
+    // tracks may need to be filled in.
+    for (i = 0; i < s->nb_streams; i++) {
+        MOVTrack *track = &mov->tracks[i];
+        if (!track->end_reliable) {
+            AVPacket *next = ff_interleaved_peek(s, i);
+            if (next) {
+                track->track_duration = next->dts - track->start_dts;
+                if (next->pts != AV_NOPTS_VALUE)
+                    track->end_pts = next->pts;
+                else
+                    track->end_pts = next->dts;
+            }
+        }
+    }
+
     for (i = 0; i < mov->nb_streams; i++) {
         MOVTrack *track = &mov->tracks[i];
         if (track->entry <= 1)
@@ -4316,6 +4335,7 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
                                              mov->tracks[i].track_duration -
                                              mov->tracks[i].cluster[0].dts;
             mov->tracks[i].entry = 0;
+            mov->tracks[i].end_reliable = 0;
         }
         avio_flush(s->pb);
         return 0;
@@ -4395,6 +4415,7 @@ static int mov_flush_fragment(AVFormatContext *s, int force)
             track->frag_start += duration;
         track->entry = 0;
         track->entries_flushed = 0;
+        track->end_reliable = 0;
         if (!mov->frag_interleave) {
             if (!track->mdat_buf)
                 continue;
@@ -4760,6 +4781,7 @@ static int mov_write_single_packet(AVFormatContext *s, AVPacket *pkt)
                     trk->end_pts = pkt->pts;
                 else
                     trk->end_pts = pkt->dts;
+                trk->end_reliable = 1;
                 mov_auto_flush_fragment(s, 0);
             }
         }
diff --git a/libavformat/movenc.h b/libavformat/movenc.h
index 1090085a5a..c4fded89bb 100644
--- a/libavformat/movenc.h
+++ b/libavformat/movenc.h
@@ -115,6 +115,7 @@ typedef struct MOVTrack {
     int64_t     start_dts;
     int64_t     start_cts;
     int64_t     end_pts;
+    int         end_reliable;
 
     int         hint_track;   ///< the track that hints this track, -1 if no hint track is set
     int         src_track;    ///< the track that this hint (or tmcd) track describes
diff --git a/libavformat/mux.c b/libavformat/mux.c
index 8488043006..10b2750e3f 100644
--- a/libavformat/mux.c
+++ b/libavformat/mux.c
@@ -1041,6 +1041,17 @@ int ff_interleave_packet_per_dts(AVFormatContext *s, AVPacket *out,
     }
 }
 
+const AVPacket *ff_interleaved_peek(AVFormatContext *s, int stream)
+{
+    AVPacketList *pktl = s->internal->packet_buffer;
+    while (pktl) {
+        if (pktl->pkt.stream_index == stream)
+            return &pktl->pkt;
+        pktl = pktl->next;
+    }
+    return NULL;
+}
+
 /**
  * Interleave an AVPacket correctly so it can be muxed.
  * @param out the interleaved packet will be output here
diff --git a/libavformat/version.h b/libavformat/version.h
index 543afbb166..544d4363eb 100644
--- a/libavformat/version.h
+++ b/libavformat/version.h
@@ -33,7 +33,7 @@
 // Also please add any ticket numbers that you belive might be affected here
 #define LIBAVFORMAT_VERSION_MAJOR  57
 #define LIBAVFORMAT_VERSION_MINOR  40
-#define LIBAVFORMAT_VERSION_MICRO 100
+#define LIBAVFORMAT_VERSION_MICRO 101
 
 #define LIBAVFORMAT_VERSION_INT AV_VERSION_INT(LIBAVFORMAT_VERSION_MAJOR, \
                                                LIBAVFORMAT_VERSION_MINOR, \