diff --git a/libavformat/rtmpproto.c b/libavformat/rtmpproto.c
index ec4b0e73f3..77a801d11c 100644
--- a/libavformat/rtmpproto.c
+++ b/libavformat/rtmpproto.c
@@ -2213,7 +2213,7 @@ static int append_flv_data(RTMPContext *rt, RTMPPacket *pkt, int skip)
     bytestream2_put_byte(&pbc, ts >> 24);
     bytestream2_put_be24(&pbc, 0);
     bytestream2_put_buffer(&pbc, data, size);
-    bytestream2_put_be32(&pbc, 0);
+    bytestream2_put_be32(&pbc, size + RTMP_HEADER);
 
     return 0;
 }
@@ -2363,8 +2363,9 @@ static int handle_metadata(RTMPContext *rt, RTMPPacket *pkt)
         bytestream_put_be24(&p, ts);
         bytestream_put_byte(&p, ts >> 24);
         memcpy(p, next, size + 3 + 4);
+        p    += size + 3;
+        bytestream_put_be32(&p, size + RTMP_HEADER);
         next += size + 3 + 4;
-        p    += size + 3 + 4;
     }
     if (p != rt->flv_data + rt->flv_size) {
         av_log(NULL, AV_LOG_WARNING, "Incomplete flv packets in "
@@ -2554,7 +2555,7 @@ static int inject_fake_duration_metadata(RTMPContext *rt)
     // Finalise object
     bytestream_put_be16(&p, 0); // Empty string
     bytestream_put_byte(&p, AMF_END_OF_OBJECT);
-    bytestream_put_be32(&p, 40); // size of data part (sum of all parts below)
+    bytestream_put_be32(&p, 40 + RTMP_HEADER); // size of data part (sum of all parts above)
 
     return 0;
 }