Uneven speed when reencoding mpeg program stream

[Carl Eugen Hoyos]

​http://thread.gmane.org/gmane.comp.video.ffmpeg.user/45738
A user uploaded a sample that reencodes into a file with uneven speed with ffmpeg and shows uneven playback with ffplay and mplayer -vc ffmpeg12, plays fine with mplayer -vc mpeg12
This is a regression since 0127b86

$ ffmpeg -i BAGUTTI\ CAREZZE_cut.mpg -qscale 2 -t 7 out.avi
ffmpeg version N-53092-gc45b823 Copyright (c) 2000-2013 the FFmpeg developers
  built on May 15 2013 17:44:48 with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl --disable-indev=jack
  libavutil      52. 32.100 / 52. 32.100
  libavcodec     55.  9.100 / 55.  9.100
  libavformat    55.  7.100 / 55.  7.100
  libavdevice    55.  0.100 / 55.  0.100
  libavfilter     3. 67.100 /  3. 67.100
  libswscale      2.  3.100 /  2.  3.100
  libswresample   0. 17.102 /  0. 17.102
  libpostproc    52.  3.100 / 52.  3.100
Input #0, mpeg, from 'BAGUTTI CAREZZE_cut.mpg':
  Duration: 00:00:07.28, start: 0.168444, bitrate: 8439 kb/s
    Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p, 720x576 [SAR 16:15 DAR 4:3], 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0:1[0x1c0]: Audio: mp2, 48000 Hz, stereo, s16p, 224 kb/s
Please use -q:a or -q:v, -qscale is ambiguous
Output #0, avi, to 'out.avi':
  Metadata:
    ISFT            : Lavf55.7.100
    Stream #0:0: Video: mpeg4 (FMP4 / 0x34504D46), yuv420p, 720x576 [SAR 16:15 DAR 4:3], q=2-31, 200 kb/s, 25 tbn, 25 tbc
    Stream #0:1: Audio: ac3 ([0] [0][0] / 0x2000), 48000 Hz, stereo, fltp, 192 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (mpeg2video -> mpeg4)
  Stream #0:1 -> #0:1 (mp2 -> ac3)
Press [q] to stop, [?] for help
frame=  171 fps=0.0 q=2.0 Lsize=    5954kB time=00:00:07.00 bitrate=6960.2kbits/s
video:5771kB audio:164kB subtitle:0 global headers:0kB muxing overhead 0.321262%

out.avi "pauses" for a moment after four seconds.

[Michael Niedermayer]

Fixed in 970c8df73528659925819dec31c4c8c0887f0321