FFprobe reports 50Hz framerate for 25Hz MPEG1 input file

[t.rapp]

Starting with FFmpeg v6.1 some MPEG1 input file is reported by FFprobe with 50Hz video framerate. In previous versions 25Hz have been reported, and converting the file with FFmpeg v6.1 into another format (like AVI) will generate a 25Hz output file.

How to reproduce:

% ffprobe -select_streams v -show_entries "stream=r_frame_rate" -i temp/2C491696.mpg

ffprobe version N-113240-g6d2f645 Copyright (c) 2007-2024 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.12) 20160609
  configuration: --enable-gpl --disable-network --enable-libsoxr --enable-libtwolame --enable-libmp3lame --enable-libvorbis --enable-libfreetype --enable-libx264 --enable-static --disable-shared --progs-suffix=-dbg --enable-debug --disable-optimizations --enable-extra-warnings --assert-level=2 --prefix=/usr/local
  libavutil      58. 36.101 / 58. 36.101
  libavcodec     60. 37.100 / 60. 37.100
  libavformat    60. 20.100 / 60. 20.100
  libavdevice    60.  4.100 / 60.  4.100
  libavfilter     9. 17.100 /  9. 17.100
  libswscale      7.  6.100 /  7.  6.100
  libswresample   4. 13.100 /  4. 13.100
  libpostproc    57.  4.100 / 57.  4.100
Input #0, mpeg, from 'temp/2C491696.mpg':
  Duration: 00:00:21.10, start: 22652.867033, bitrate: 1260 kb/s
  Stream #0:0[0x1e0]: Video: mpeg1video, yuv420p(tv, progressive), 720x576 [SAR 1:1 DAR 5:4], 104857 kb/s, 25 fps, 50 tbr, 90k tbn
      Side data:
        cpb: bitrate max/min/avg: 0/0/0 buffer size: 278528 vbv_delay: N/A
  Stream #0:1[0x1c0]: Audio: mp2, 48000 Hz, stereo, s16p, 192 kb/s
[STREAM]
r_frame_rate=50/1
[SIDE_DATA]
[/SIDE_DATA]
[/STREAM]

Running git bisect points to commit e930b834a928546f9cbc937f6633709053448232 having introduced the changed output value.

[t.rapp]

Report log file of a run with current ffprobe version (2024-01-09)

[mrapp]

I just noticed this for WMV/vc1 files. My local ffprobe version is 4.4.4 and was giving me the expected r_frame_rate value of "30000/1001", but our production machines had ffprobe 6.1 and were returning "60000/1001" for the same file.