video - WTV and DVR-MS television recordings, should I de-interlace or not?

Following on from this question (where I am converting WTV and DVR-MS television recordings into H.264/MPEG-4 AVC to cut down on space), given the output of ffmpeg -i , how can I work out whether or not I should de-interlace the converted file?

The output for one such file is displayed below:

Input #0, asf, from 'Episodes_BBC TWO_2012_06_29_21_59_00.dvr-ms':
  Metadata:
    DVR Index Granularity: 500
    WM/SubTitleDescription: 8/9. Matt's life continues to fall apart when he fal
ls foul of his fierce ex-wife. Beverly prepares to go on a second date with Morn
ing's brother Rob. Contains strong language.  Also in HD. [AD,S]
    genre           : Shows;Other Shows
    WM/OriginalReleaseTime: 0
    WM/MediaCredits : ;;;
    service_provider: BBC TWO
    service_name    : BBC TWO
    WM/MediaNetworkAffiliation: BBC TWO
    WM/MediaOriginalChannel: 2
    WM/MediaOriginalChannelSubNumber: 0
    WM/MediaOriginalBroadcastDateTime: 0001-01-01T00:00:00Z
    WM/MediaOriginalRunTime: 1991686
    WM/MediaIsStereo: 0
    WM/MediaIsRepeat: 0
    WM/MediaIsLive  : 0
    WM/MediaIsTape  : 0
    WM/MediaIsDelay : 0
    WM/MediaIsSubtitled: 0
    WM/MediaIsMovie : 0
    WM/MediaIsPremiere: 0
    WM/MediaIsFinale: 0
    WM/MediaIsSAP   : 0
    WM/MediaIsSport : 0
    WM/Provider     : Default
    WM/VideoClosedCaptioning: 0
    WM/WMRVEncodeTime: 6349638
    WM/WMRVSeriesUID: !GenericSeries!Episodes
    WM/WMRVServiceID: !Generated!73b6594426b64c11b54ca352d79bb758
    WM/WMRVProgramID: !Loaders!Glid!Programs!9018:4164:4287!60652
    WM/WMRVRequestID: 0
    WM/WMRVScheduleItemID: 0
    WM/WMRVQuality  : 0
    WM/WMRVOriginalSoftPrePadding: 360
    WM/WMRVOriginalSoftPostPadding: 60
    WM/WMRVHardPrePadding: 184
    WM/WMRVHardPostPadding: 0
    WM/WMRVATSCContent: 0
    WM/WMRVDTVContent: 1
    WM/WMRVHDContent: 0
    WM/WMRVEndTime  : 1844674
    WM/WMRVBitrate  : 1844674
    WM/WMRVKeepUntil: 0
    WM/WMRVActualSoftPrePadding: 382
    WM/WMRVActualSoftPostPadding: 63
    WM/WMRVContentProtected: 0
    WM/WMRVContentProtectedPercent: 0
    WM/WMRVExpirationDate: 1844674
    WM/WMRVExpirationSpan: 1844674
    WM/WMRVInBandRatingSystem: 255
    WM/WMRVInBandRatingLevel: 255
    WM/WMRVInBandRatingAttributes: 0
    WM/WMRVWatched  : 0
    WM/MediaThumbType: 3
    WMFSDKVersion   : 12.0.7601.17514
    WMFSDKNeeded    : 0.0.0.0000
    VBR Peak        : 159
    IsVBR           : 1
    title           : Episodes
  Duration: 00:31:56.21, start: 0.000000, bitrate: 2658 kb/s
    Stream #0:0(eng): Audio: mp2, 48000 Hz, stereo, s16, 256 kb/s
    Stream #0:1(eng): Unknown: none
    Stream #0:2(eng): Video: mpeg2video (DVR  / 0x20525644), yuv420p, 704x480 [S
AR 64:45 DAR 1408:675], 15000 kb/s, 25.03 fps, 125 tbr, 1k tbn, 50 tbc

Answer

Quoting Carl-Eugen Hoyos, one of the FFmpeg developers (if I'm not mistaken, at least he's the most active person on the FFmpeg mailing list):

Decoding is necessary to determine if the input is interlaced, if you you encode immediately or later is your decision...

So, no – you can't tell that on-the-fly. What you'd have to do is try to decode the video to reliably get the information.

While I don't see anything particular in your output, one could guess from the difference in tbc and actual frame rate that interlacing is used for this particular video clip.

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That being said, some containers might have the proper information about interlacing set. Check the mediainfo output for the video file and look for Scan type and Scan order metadata fields. The former should either show interlaced or progressive.