Converted TS to MP4, what is the meaning of new (and multiple SAR, DAR ) in the output video?

Question

I have a file with extension .ts, information given by ffmpeg -i MyMovieFile.ts is:

[mpegts @ 000001f8fc13fa80] start time for stream 0 is not set in estimate_timings_from_pts
Input #0, mpegts, from 'MyMovieFile.ts':
  Duration: 01:49:27.52, start: 0.000000, bitrate: 4319 kb/s
  Program 1
  Stream #0:0[0x102]: Data: timed_id3 (ID3  / 0x20334449)
  Stream #0:1[0x100]: Video: h264 (High) ([27][0][0][0] / 0x001B), yuv420p(tv, bt709, progressive), 1920x1052 [SAR 997:1024 DAR 14955:8416], 25 fps, 25 tbr, 90k tbn
  Stream #0:2[0x101]: Audio: aac (LC) ([15][0][0][0] / 0x000F), 44100 Hz, stereo, fltp, 191 kb/s

I converted to MP4 using ffmpeg with

-vf scale=1280:720 ^
-map 0:1 -map 0:2 ^
-c:v libx264 -c:a aac ^

After conversion, VLC codec information shows: Video Resolution = 1280x720 (= Buffer Resolution).

I am happy with this result; If I now run the converted file thru ffmpeg -i, I get

 Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf59.24.100
  Duration: 01:49:27.52, start: 0.000000, bitrate: 2178 kb/s
  Stream #0:0[0x1](und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709, progressive), 1280x720 [SAR 2206:2207 DAR 35296:19863], 2042 kb/s, SAR 28684:28697 DAR 458944:258273, 25 fps, 25 tbr, 12800 tbn (default)
    Metadata:
      handler_name    : VideoHandler
      vendor_id       : [0][0][0][0]
  Stream #0:1[0x2](und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 128 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
      vendor_id       : [0][0][0][0]

My question is why am I getting two pairs of SAR/DAR

[SAR 2206:2207 DAR 35296:19863]  
SAR 28684:28697 DAR 458944:258273

And would it be better to also specify the expected SAR,DAR during ffmpeg conversion? For example, [SAR 1:1 DAR 16:9]

Answer 1

The values in the bracket comes from the stream decoder. The values may also be stored in the MP4 container, specifically the PASP box with a different precision. If they differ, ffmpeg will print both.

In this case, they differ at the 7th digit after the decimal point.

  2206/2207 = 0.9995468962392388
28684/28697 = 0.9995469909746663