[FFmpeg-user] Fw: Re: Confusion about fieldmatch, decimate and framerate

[Nicholas Robbins]

--- On Thu, 11/7/13, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:

> From: Carl Eugen Hoyos <cehoyos at ag.or.at>
> Subject: Re: [FFmpeg-user] Confusion about fieldmatch, decimate and framerate
> To: ffmpeg-user at ffmpeg.org
> Date: Thursday, November 7, 2013, 9:10 AM
> Nicholas Robbins <nickrobbins
> <at> yahoo.com> writes:
> 
> > Uploaded to upload.ffmpeg.org/incoming as
> sample-robbins.mkv
> 
> The sample claims to be 60fps while it actually is 30fps.
> Assuming you produced the mkv file from a MPEG original:
> Is the problem also reproducible with the original mpeg 
> file?


So I get the original file using mplayer's dumpstream. It gives me a VOB. ffprobe has this to say about the vob:
Input #0, mpeg, from 'Magic.vob':
  Duration: 00:01:00.64, start: 0.280633, bitrate: 5533 kb/s
    Stream #0:0[0x1e0]: Video: mpeg2video (Main), yuv420p, 720x480 [SAR 32:27 DAR 16:9], 29.67 fps, 59.94 tbr, 90k tbn, 59.94 tbc
    Stream #0:1[0x80]: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s

If I run mkvmerge on this then ffprobe says:
Input #0, matroska,webm, from 'Magic-Merged.mkv':
  Metadata:
    creation_time   : 2013-11-07 22:42:20
  Duration: 00:01:00.76, start: 0.000000, bitrate: 5430 kb/s
    Stream #0:0: Video: mpeg2video (Main), yuv420p, 720x480 [SAR 32:27 DAR 16:9], SAR 186:157 DAR 279:157, 59.94 fps, 59.94 tbr, 1k tbn, 59.94 tbc (default)
    Stream #0:1: Audio: ac3, 48000 Hz, 5.1(side), fltp, 448 kb/s (default)

If I run ffmpeg with fieldmatch on the original vob I get:

Input #0, matroska,webm, from 'Magic-Fieldmatch.mkv':
  Metadata:
    ENCODER         : Lavf55.12.100
  Duration: 00:01:00.86, start: 0.000000, bitrate: 1457 kb/s
    Stream #0:0: Video: h264 (High), yuv420p, 720x480 [SAR 32:27 DAR 16:9], SAR 186:157 DAR 279:157, 29.97 fps, 29.97 tbr, 1k tbn, 59.94 tbc (default)

Now adding in decimate

Input #0, matroska,webm, from 'Magic-Fieldmatch-Decimate.mkv':
  Metadata:
    ENCODER         : Lavf55.12.100
  Duration: 00:00:48.76, start: 0.000000, bitrate: 1531 kb/s
    Stream #0:0: Video: h264 (High), yuv420p, 720x480 [SAR 32:27 DAR 16:9], SAR 186:157 DAR 279:157, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)

(wrong length)

Adding in fps option:

Input #0, matroska,webm, from 'Magic-Fieldmatch-Decimate-fps.mkv':
  Metadata:
    ENCODER         : Lavf55.12.100
  Duration: 00:01:00.89, start: 0.000000, bitrate: 1424 kb/s
    Stream #0:0: Video: h264 (High), yuv420p, 720x480 [SAR 32:27 DAR 16:9], SAR 186:157 DAR 279:157, 23.98 fps, 23.98 tbr, 1k tbn, 47.95 tbc (default)

Seems like this is only a problem when I do Fieldmatching. I've never had this problem before when I don't use any filters or use only yadif. I would like an auto-magic step that make sure that the fps is set correctly.

Thanks for all  your help so far. At this point this is just icing on the cake.