Change the default codecs for the rtsp muxer to mpeg4 and aac

These codecs in RTP are supported by many players.

Originally committed as revision 23209 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/rtspenc.c

@@ -168,8 +168,8 @@ AVOutputFormat rtsp_muxer = {
     NULL,
     NULL,
     sizeof(RTSPState),
-    CODEC_ID_PCM_MULAW,
-    CODEC_ID_NONE,
+    CODEC_ID_AAC,
+    CODEC_ID_MPEG4,
     rtsp_write_header,
     rtsp_write_packet,
     rtsp_write_close,