My ffserver.conf
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HTTPPort 8090
# bind to all IPs aliased or not
HTTPBindAddress 0.0.0.0
# max number of simultaneous clients
MaxClients 1000
# max bandwidth per-client (kb/s)
MaxBandwidth 10000
# Suppress that if you want to launch ffserver as a daemon.
#NoDaemon
CustomLog /Users/pulsar/GoogleDrive/github/logs/ffserver_log.txt

<Feed feed1.ffm>
   File /tmp/feed1.ffm
   FileMaxSize 5M
</Feed>

<Stream test.flv>
Feed feed1.ffm
Format flv
#NoVideo
VideoCodec flv1
AVOptionVideo flags +global_header
PixelFormat yuv420p
VideoFrameRate 25
VideoGopSize 12
VideoBufferSize 0
VideoBitRate 1872
NoDefaults
StartSendOnKey
AVOptionVideo trellis 1
#AVOptionVideo 8x8dct 1
#AVOptionVideo mbtree 0
VideoQMin 1
VideoQMax 10
VideoSize 1280x800
PreRoll 0
Noaudio
</Stream>
<Stream status.html>            # Server status URL
Format status
#Only allow local people to get the status
#ACL allow 10.10.10.0 10.10.10.50
</Stream>
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ffmpeg command output:

/ffmpeg -f avfoundation -i "1:"  -maxrate 2500k -threads:0 4 -threads:1 4 -vcodec copyts -movflags +faststart -pix_fmt yuv420p http://localhost:8090/feed1.ffm
ffmpeg version N-71403-g415f1fa Copyright (c) 2000-2015 the FFmpeg developers
  built with Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM 3.5svn)
  configuration: --prefix=/usr/local --enable-gpl --enable-postproc --enable-pthreads --enable-libmp3lame --enable-libtheora --enable-libx264 --enable-libvorbis --disable-armv5te --disable-armv6 --disable-neon --enable-static --disable-stripping --disable-shared
  libavutil      54. 22.101 / 54. 22.101
  libavcodec     56. 34.100 / 56. 34.100
  libavformat    56. 30.100 / 56. 30.100
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 13.101 /  5. 13.101
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
[avfoundation @ 0x7fcfca82bc00] Selected pixel format (yuv420p) is not supported by the input device.
[avfoundation @ 0x7fcfca82bc00] Supported pixel formats:
[avfoundation @ 0x7fcfca82bc00]   uyvy422
[avfoundation @ 0x7fcfca82bc00]   yuyv422
[avfoundation @ 0x7fcfca82bc00]   nv12
[avfoundation @ 0x7fcfca82bc00]   0rgb
[avfoundation @ 0x7fcfca82bc00]   bgr0
[avfoundation @ 0x7fcfca82bc00] Overriding selected pixel format to use uyvy422 instead.
[avfoundation @ 0x7fcfca82bc00] Stream #0: not enough frames to estimate rate; consider increasing probesize
Input #0, avfoundation, from '1:':
  Duration: N/A, start: 36499.697833, bitrate: N/A
    Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 1440x900, 1000k tbr, 1000k tbn, 1000k tbc
[tcp @ 0x7fcfca45f1a0] Connection to tcp://localhost:8090 failed (Connection refused), trying next address
[tcp @ 0x7fcfca70ece0] Connection to tcp://localhost:8090 failed (Connection refused), trying next address
[ffm @ 0x7fcfca84d200] Frame rate very high for a muxer not efficiently supporting it.
Please consider specifying a lower framerate, a different muxer or -vsync 2
[flv @ 0x7fcfcc02f000] Either both buffer size and max rate or neither must be specified
Output #0, ffm, to 'http://localhost:8090/feed1.ffm':
  Metadata:
    creation_time   : now
    Stream #0:0: Video: flv1 (flv), yuv420p, 1280x800, q=1-10, 1872 kb/s, 1000k fps, 25 tbc
    Metadata:
      encoder         : Lavc56.34.100 flv
Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> flv1 (flv))
Error while opening encoder for output stream #0:0 - maybe incorrect parameters such as bit_rate, rate, width or height