Fix MPEG video packetization for RTP

Originally committed as revision 14149 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/rtp_mpv.c

@@ -66,7 +66,7 @@ void ff_rtp_send_mpegvideo(AVFormatContext *s1, const uint8_t *buf1, int size)
                         begin_of_sequence = 1;
                     }
 
-                    if (r - buf1 < len) {
+                    if (r - buf1 - 4 <= len) {
                         /* The current slice fits in the packet */
                         if (begin_of_slice == 0) {
                             /* no slice at the beginning of the packet... */
@@ -76,7 +76,7 @@ void ff_rtp_send_mpegvideo(AVFormatContext *s1, const uint8_t *buf1, int size)
                         }
                         r1 = r;
                     } else {
-                        if (r - r1 < max_packet_size - 4) {
+                        if ((r1 - buf1 > 4) && (r - r1 < max_packet_size)) {
                             len = r1 - buf1 - 4;
                             end_of_slice = 1;
                         }