[FFmpeg-user] Problem decoding H263+ Codec from RTP stream

[M. V.]

Hello everyone,
I'm trying to decode RTP video stream to a playable format with the help of ffmpeg. this works perfect for H263 codec. I simply write H263 payloads of RTP packets of my H263 stream in a file, and give it to ffmpeg to decode. and ffmpeg gives me an flv output.
but for H263+ codec, this doesn't work and ffmpeg gives me "Header damaged" error. (I tried to make input file with and without 2 Bytes of H263+ header, but got no luck)  any ideas?
Thanks.

what I execute is :
root# ffmpeg -f h263 -i input_video.rtp output.flv
ffmpeg version 3.0 Copyright (c) 2000-2016 the FFmpeg developers
  built with gcc 4.7 (Debian 4.7.2-5)
  configuration: --disable-yasm --enable-libtheora
  libavutil      55. 17.103 / 55. 17.103
  libavcodec     57. 24.102 / 57. 24.102
  libavformat    57. 25.100 / 57. 25.100
  libavdevice    57.  0.101 / 57.  0.101
  libavfilter     6. 31.100 /  6. 31.100
  libswscale      4.  0.100 /  4.  0.100
  libswresample   2.  0.101 /  2.  0.101
[h263 @ 0x20b5a80] Bad picture start code
[h263 @ 0x20b5a80] header damaged
[h263 @ 0x20ac5a0] decoding for stream 0 failed
[h263 @ 0x20ac5a0] Could not find codec parameters for stream 0 (Video: h263, none): unspecified size
Consider increasing the value for the 'analyzeduration' and 'probesize' options
input_video.rtp: could not find codec parameters
Input #0, h263, from 'input_video.rtp':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: h263, none, 15 tbr, 1200k tbn, 15 tbc