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Old 2nd June 2013, 09:42   #1  |  Link
MrC
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FFmpeg and interlaced encoding

Using FFmpeg to produce an interlaced mpeg2 output, from an interlaced source (i.e. DV), I have a doubt regarding the flags to use.

-ilme -top 1

does produce a valid interlaced output TFF, according to MediaInfo.

From FFmpeg online documentation, 'ildct' and 'alt' parameters can be used as well:

-flags +ilme+ildct+alt -top 1

The question is: in your experience, are 'ildct' and 'alt' really needed to produce a good quality interlaced output?



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Old 3rd June 2013, 14:50   #2  |  Link
fvisagie
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In my experience ilme & ildct suffice. The page you link to is the FAQ; from the reference documentation:

Code:
‘flags flags (decoding/encoding,audio,video,subtitles)’

    Set generic flags.

    Possible values:

    ...

    ‘ildct’

        Use interlaced DCT. 
    ...

    ‘ilme’

        Apply interlaced motion estimation. 
    ...
Although I haven't tried to verify this, I suspect ilme ensures field-based - as opposed to frame-based - motion estimation. Using it certainly improves the quality of interlaced encodes for me.

I have no knowledge of alt and I don't see it listed in the documentation either. Perhaps it's been deprecated and its mention in the FAQ is a left-over?

PS. As I understand it, all DV sources are BFF? E.g. http://www.dvmp.co.uk/digital-video.htm, last paragraph in 'DV & DVCAM'. For my DV camera I use '-top 0'.

PPS. I also found a DV clip that MediaInfo (incorrectly) reports as TFF. To determine correct field order, use
Code:
AssumeTFF()
SeparateFields()
on scenes with motion. If motion progresses forward, backward, forward, backward etc., the clip is BFF.

Cheers,
Francois

Last edited by fvisagie; 3rd June 2013 at 15:24. Reason: PPS
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Old 4th June 2013, 21:45   #3  |  Link
MrC
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@fvisagie

thanks for the very useful inputs. The origin of the question can be found here.

'alt' is now deprecated and substitued by 'alternate_scan 1' even if it is not mentioned in the official documentation.



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