mpeg4 encoder fix by Michael Niedermayer <michaelni@gmx.at>

Originally committed as revision 254 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/mpegvideo.c

@@ -260,6 +260,7 @@ int MPV_encode_init(AVCodecContext *avctx)
     s->gop_size = avctx->gop_size;
     s->rtp_mode = avctx->rtp_mode;
     s->rtp_payload_size = avctx->rtp_payload_size;
+    s->avctx = avctx;
     
     if (s->gop_size <= 1) {
         s->intra_only = 1;