No duration for G.729 samples

[Carl Eugen Hoyos]

As reported by Dave Horton (who provided the sample), raw G.729 files do not show a duration which can lead to warnings on encoding.

$ ffmpeg -f g729 -i callee.raw -ar 44100 out.wav
ffmpeg version N-87628-g148c8e8 Copyright (c) 2000-2017 the FFmpeg developers
  built with gcc 6.3.0 (GCC)
  configuration: --enable-gpl --cc=/usr/local/gcc-6.3.0/bin/gcc
  libavutil      55. 77.101 / 55. 77.101
  libavcodec     57.106.104 / 57.106.104
  libavformat    57. 83.100 / 57. 83.100
  libavdevice    57.  9.101 / 57.  9.101
  libavfilter     6.106.100 /  6.106.100
  libswscale      4.  7.103 /  4.  7.103
  libswresample   2.  8.100 /  2.  8.100
  libpostproc    54.  6.100 / 54.  6.100
[g729 @ 0x30a7400] Estimating duration from bitrate, this may be inaccurate
Guessed Channel Layout for Input Stream #0.0 : mono
Input #0, g729, from 'callee.raw':
  Duration: 00:00:20.48, start: 0.000000, bitrate: 8 kb/s
    Stream #0:0: Audio: g729, 8000 Hz, mono, s16
Stream mapping:
  Stream #0:0 -> #0:0 (g729 (native) -> pcm_s16le (native))
Press [q] to stop, [?] for help
Output #0, wav, to 'out.wav':
  Metadata:
    ISFT            : Lavf57.83.100
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 44100 Hz, mono, s16, 705 kb/s
    Metadata:
      encoder         : Lavc57.106.104 pcm_s16le
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -82; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -77; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -71; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -66; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -60; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -55; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -49; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -44; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -38; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -33; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -27; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -22; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -16; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -11; changing to 0. This may result in incorrect timestamps in the output file.
[wav @ 0x30b2600] Non-monotonous DTS in output stream 0:0; previous: 0, current: -5; changing to 0. This may result in incorrect timestamps in the output file.
size=    1764kB time=00:00:00.26 bitrate=54354.2kbits/s speed=5.06x
video:0kB audio:1764kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.004318%

The estimated duration of 20 seconds is correct, the shown encoded duration is wrong, also reproducible with FFplay.

[Elon Musk]

Fixed in 35a12d2071efa5c408e6dd4a4a6d0cf930fb3eb3.