packet size should be buffer size, not the size of a pointer...

src/zm_mpeg.cpp

@@ -488,7 +488,7 @@ double VideoStream::ActuallyEncodeFrame( const uint8_t *buffer, int buffer_size,
     pkt->flags |= AV_PKT_FLAG_KEY;
     pkt->stream_index = ost->index;
     pkt->data = (uint8_t *)opicture_ptr;
-    pkt->size = sizeof (AVPicture);
+    pkt->size = buffer_size;
     got_packet = 1;
 	} else {
 		opicture_ptr->pts = codec_context->frame_number;