flvenc: Factorize timestamp writing

The code is trivial but the semantics in the spec are ambiguous. This
should help keep parts of the muxer interpreting them consistently.

libavformat/flvenc.c

@@ -230,12 +230,17 @@ static void put_amf_string(AVIOContext *pb, const char *str)
     avio_write(pb, str, len);
 }
 
+// FLV timestamps are 32 bits signed, RTMP timestamps should be 32-bit unsigned
+static void put_timestamp(AVIOContext *pb, int64_t ts) {
+    avio_wb24(pb, ts & 0xFFFFFF);
+    avio_w8(pb, (ts >> 24) & 0x7F);
+}
+
 static void put_avc_eos_tag(AVIOContext *pb, unsigned ts)
 {
     avio_w8(pb, FLV_TAG_TYPE_VIDEO);
     avio_wb24(pb, 5);               /* Tag Data Size */
-    avio_wb24(pb, ts);              /* lower 24 bits of timestamp in ms */
-    avio_w8(pb, (ts >> 24) & 0x7F); /* MSB of ts in ms */
+    put_timestamp(pb, ts);
     avio_wb24(pb, 0);               /* StreamId = 0 */
     avio_w8(pb, 23);                /* ub[4] FrameType = 1, ub[4] CodecId = 7 */
     avio_w8(pb, 2);                 /* AVC end of sequence */
@@ -492,8 +497,7 @@ static void flv_write_codec_header(AVFormatContext* s, AVCodecParameters* par) {
                 par->codec_type == AVMEDIA_TYPE_VIDEO ?
                         FLV_TAG_TYPE_VIDEO : FLV_TAG_TYPE_AUDIO);
         avio_wb24(pb, 0); // size patched later
-        avio_wb24(pb, 0); // ts
-        avio_w8(pb, 0);   // ts ext
+        put_timestamp(pb, 0);
         avio_wb24(pb, 0); // streamid
         pos = avio_tell(pb);
         if (par->codec_id == AV_CODEC_ID_AAC) {
@@ -978,8 +982,7 @@ static int flv_write_packet(AVFormatContext *s, AVPacket *pkt)
     }
 
     avio_wb24(pb, size + flags_size);
-    avio_wb24(pb, ts & 0xFFFFFF);
-    avio_w8(pb, (ts >> 24) & 0x7F); // timestamps are 32 bits _signed_
+    put_timestamp(pb, ts);
     avio_wb24(pb, flv->reserved);
 
     if (par->codec_type == AVMEDIA_TYPE_DATA ||