no duration for FLV file

[cgbug]

Sample:
​http://www.datafilehost.com/d/e2ed3397

MediaInfo shows a duration of 2m20s.

FFmpeg output:

ffmpeg version N-72362-g7ae805d Copyright (c) 2000-2015 the FFmpeg developers
  built with gcc 4.9.2 (GCC)
  configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libdcadec --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmfx --enable-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-lzma --enable-decklink --enable-zlib
  libavutil      54. 25.100 / 54. 25.100
  libavcodec     56. 41.100 / 56. 41.100
  libavformat    56. 33.101 / 56. 33.101
  libavdevice    56.  4.100 / 56.  4.100
  libavfilter     5. 16.101 /  5. 16.101
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
[flv @ 02d33700] Stream discovered after head already parsed
[flv @ 02d33700] Negative cts, previous timestamps might be wrong.
[flv @ 02d33700] Invalid timestamps stream=0, pts=-481, dts=0, size=1273
[flv @ 02d33700] Invalid timestamps stream=0, pts=-364, dts=0, size=1478
[flv @ 02d33700] Invalid timestamps stream=0, pts=-242, dts=0, size=1367
[flv @ 02d33700] Invalid timestamps stream=0, pts=-113, dts=0, size=1330
Input #0, flv, from 'no_duration.flv':
  Metadata:
    encoder         : Lavf52.93.0
  Duration: 00:00:00.00, start: 0.000000, bitrate: N/A
    Stream #0:0: Video: h264 (Baseline), yuv420p(tv), 640x360 [SAR 1:1 DAR 16:9], 20 fps, 20 tbr, 1k tbn, 40 tbc
    Stream #0:1: Audio: aac (LC), 44100 Hz, stereo, fltp, 48 kb/s
    Stream #0:2: Subtitle: text
At least one output file must be specified

[Carl Eugen Hoyos]

Regression since f3c51215cef3add584a9e939476baf1f07ab56a9

[Ganesh Ajjanagadde]

Fixed in a86928d2abf81ea92e9bf90d3dc5bb71ea7f2457