rtmpproto: Write correct flv packet sizes at the end of packets

In one case it was written as zero, one case left it uninitialized,
missed the 11 bytes for the flv header.
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

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;
 }