[FFmpeg-user] about flv file metadata

[esolve esolve]

  I use ffmpeg to retrieve information about adobe flash videos, and get

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Input #0, flv, from 'flash':
  Metadata:
    duration        : 205
    videodatarate   : 1040
    audiodatarate   : 118
    totaldatarate   : 1163
    bytelength      : 29833281
  ........
  Duration: 00:03:24.72, start: 0.000000, bitrate: 1185 kb/s
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there are two bitrates: 1185kb/s and 1163 kb/s
but if I divide the bytelength by the duration 29833281*8/205/1024, I get
1136.939 kb/s, it is either 1185kb/s or 1163 kb/s
what is the relationship between these three values?

BTW, do you know how to show the real duration of a incomplete flv file?
thank you!