$ ffmpeg -i http://cdnbakmi.kaltura.com/p/243342/sp/24334200/serveFlavor/entryId/0_ntovmku5/flavorId/0_yiep8zj7/name/a.webm -i image.png -filter_complex "overlay=(main_w-overlay_w)/2:(main_h-overlay_h)/2" http://localhost:9090/feed0.ffm
ffmpeg version N-47551-gda9a45b Copyright (c) 2000-2012 the FFmpeg developers
  built on Dec 11 2012 19:38:17 with gcc 4.7 (Ubuntu/Linaro 4.7.2-2ubuntu1)
  configuration: --enable-gpl --enable-libmp3lame --enable-libvpx --enable-libx264 --enable-version3 --enable-libvorbis
  libavutil      52. 11.102 / 52. 11.102
  libavcodec     54. 79.100 / 54. 79.100
  libavformat    54. 47.100 / 54. 47.100
  libavdevice    54.  3.102 / 54.  3.102
  libavfilter     3. 25.101 /  3. 25.101
  libswscale      2.  1.103 /  2.  1.103
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  2.100 / 52.  2.100
Input #0, matroska,webm, from 'http://cdnbakmi.kaltura.com/p/243342/sp/24334200/serveFlavor/entryId/0_ntovmku5/flavorId/0_yiep8zj7/name/a.webm':
  Duration: 00:01:41.23, start: 0.000000, bitrate: 1241 kb/s
    Stream #0:0(eng): Video: vp8, yuv420p, 624x352, SAR 1:1 DAR 39:22, 23.98 fps, 23.98 tbr, 1k tbn, 1k tbc (default)
    Stream #0:1(eng): Audio: vorbis, 48000 Hz, stereo, fltp (default)
Input #1, image2, from 'image.png':
  Duration: 00:00:00.04, start: 0.000000, bitrate: N/A
    Stream #1:0: Video: png, rgba, 320x240 [SAR 2835:2835 DAR 4:3], 25 tbr, 25 tbn, 25 tbc
Tue Dec 11 20:00:27 2012 127.0.0.1 - - [GET] "/feed0.ffm HTTP/1.1" 200 4175
[libvpx @ 0x9e98fc0] v1.1.0
Output #0, ffm, to 'http://localhost:9090/feed0.ffm':
  Metadata:
    creation_time   : now
    encoder         : Lavf54.47.100
    Stream #0:0(eng): Video: mpeg1video, yuv420p, 624x352 [SAR 1:1 DAR 39:22], q=2-31, 200 kb/s, 1000k tbn, 23.98 tbc (default)
    Stream #0:1(eng): Audio: vorbis, 22050 Hz, mono, fltp, 64 kb/s (default)
    Stream #0:2(eng): Video: vp8, yuv420p, 256x144 [SAR 351:352 DAR 39:22], q=2-31, 400 kb/s, 1000k tbn, 23.98 tbcTue Dec 11 20:00:27 2012 Feed '/tmp/feed0.ffm' stream number does not match registered feed
 (default)
Tue Dec 11 20:00:27 2012 127.0.0.1 - - [POST] "/feed0.ffm HTTP/1.1" 200 4096
Stream mapping:
  Stream #0:0 (vp8) -> overlay:main (graph 0)
  Stream #1:0 (png) -> overlay:overlay (graph 0)
  overlay (graph 0) -> Stream #0:0 (mpeg1video)
  Stream #0:1 -> #0:1 (vorbis -> libvorbis)
  Stream #0:0 -> #0:2 (vp8 -> libvpx)
Press [q] to stop, [?] for help
[libvorbis @ 0x9e988c0] Que input is backward in time
    Last message repeated 1 times
[ffm @ 0x9e69f80] st:0 PTS: 223401 DTS: 223401 < 224355 invalid, clipping
[libvorbis @ 0x9e988c0] Que input is backward in time
    Last message repeated 5 times
av_interleaved_write_frame(): Connection reset by peer