not all video. enables to restream/transcode rtsp/h264 streams.
  Should also partly fix #397, it seems that most of h264 streams are
  with packetization-mode=1 eg. in decoding order (thou it should be
  checked here, and FIXME is for that).

- only start GET_PARAMETER keepalive-thread if x-asf is setted eg. when
  server is wms, DSS 5.5.4 & 5.5.5 doesn't like GET_PARAMETER at all and
  closes the connection when getting that, and they seem to use
  rtcp-data for liveness. Kasenna uses that KA in useragent-string.