rtmppkt: Repeat the full 32 bit timestamp for chunking continuation packets

This fixes sending chunked packets (packets larger than the output
chunk size, which often can be e.g. 4096 bytes) with a timestamp delta
(or absolute timstamp, if it's a timestamp step backwards, or the
first packet of the stream) larger than 0xffffffff.

The RTMP spec explicitly says (in section 5.3.1.3.) that packets of
type 3 (continuation packets) should include this field, if the
previous non-continuation packet had it included.

The receiving code handles these packets correctly.

Pointed out by Cheolho Park.

CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/rtmppkt.c

@@ -386,6 +386,13 @@ int ff_rtmp_packet_write(URLContext *h, RTMPPacket *pkt,
             if ((ret = ffurl_write(h, &marker, 1)) < 0)
                 return ret;
             written++;
+            if (pkt->ts_field == 0xFFFFFF) {
+                uint8_t ts_header[4];
+                AV_WB32(ts_header, timestamp);
+                if ((ret = ffurl_write(h, ts_header, 4)) < 0)
+                    return ret;
+                written += 4;
+            }
         }
     }
     return written;