sapenc: Pass the title on to the chained muxers

This makes sure it ends up in the SDP, providing a proper session name
in the SAP announcements.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/sapenc.c

@@ -23,6 +23,7 @@
 #include "libavutil/parseutils.h"
 #include "libavutil/random_seed.h"
 #include "libavutil/avstring.h"
+#include "libavutil/dict.h"
 #include "libavutil/intreadwrite.h"
 #include "libavutil/time.h"
 #include "internal.h"
@@ -76,6 +77,7 @@ static int sap_write_header(AVFormatContext *s)
     struct sockaddr_storage localaddr;
     socklen_t addrlen = sizeof(localaddr);
     int udp_fd;
+    AVDictionaryEntry* title = av_dict_get(s->metadata, "title", NULL, 0);
 
     if (!ff_network_init())
         return AVERROR(EIO);
@@ -158,6 +160,9 @@ static int sap_write_header(AVFormatContext *s)
         av_strlcpy(contexts[i]->filename, url, sizeof(contexts[i]->filename));
     }
 
+    if (s->nb_streams > 0 && title)
+        av_dict_set(&contexts[0]->metadata, "title", title->value, 0);
+
     ff_url_join(url, sizeof(url), "udp", NULL, announce_addr, port,
                 "?ttl=%d&connect=1", ttl);
     ret = ffurl_open(&sap->ann_fd, url, AVIO_FLAG_WRITE,