Dazzle DVC100 BFF vs. TFF

[Zabar12]

I capture from VHS in iuVCR with huffyuv 2.2.1
Can anyone explain why I get all captures in BFF (as reported by info() in avisynth)?
Is it hardcoded in Dazzle?

[jagabo]

Capture devices/drivers decide whether capture top field first, or bottom field first.

[Zabar12]

Does it mean there is no way to make it capture TFF?

[jagabo]

Does it mean there is no way to make it capture TFF?

There is nothing you can do (DV is always BFF) except switch the field order later. But that will require a re-encode.

Is your problem progressive PAL frames appearing interlaced because they are broadcast TFF and you're capturing BFF?

[Zabar12]

I capture interlaced PAL VHS in 720x576 with lossless compression. The reason I'm concerned with BFF is that I'm having some problems with resizing in Carbon Coder while getting mpeg. Though, as Dazzle is designed to work with DV it's possible that BFF is it's default format.

[jagabo]

You can convert BFF to TFF by shifting the frame up by one scan line. Since you're capturing lossless you must be planning on compression go something else for final storage so the extra step shouldn't be a problem.

If you know AviSynth you can also use SeparateFields().Trim(1,0).Weave(). If the source is progressive frames that will restore them.

[Zabar12]

I applied another script:
DirectShowSource("Video.avi")
AssumeTFF() #AssumeBFF()
SeparateFields()

and found that info() produced wrong information about BFF

[jagabo]

So the frames are really TFF? Or are they progressive?

[Zabar12]

Info() reported BFF, but manual verification confirmed TFF

[poisondeathray]

Info() reported BFF, but manual verification confirmed TFF

Avisynth's Info() always reports BFF by default . Info() doesn't tell you anything about actual field order of the clip, you can only determine that manually

[Zabar12]

Info() doesn't tell you anything about actual field order of the clip, you can only determine that manually

That's the lesson I learned today.
Apparently, this fact is not documented here
http://avisynth.org/mediawiki/Info

[poisondeathray]

Yes, the mediawiki documenation should be more clear

If you want a basic guide for dermining field order, progressive, interlaced, pulldown...

http://neuron2.net/faq.html#analysis

[Zabar12]

Thanks, I employed a similar method described in this FAQ to sort out my problem

[2Bdecided]

Avisynth's Info() always reports BFF by default.

Not quite. AVIsynth's AVISource always sets AVIsynth's internal field order flag to BFF. Some other source filters (e.g. MPEG2Source) read the field order correctly from the file, and so sometimes set it to TFF.

There should be no problem working with BFF footage. You can put BFF video onto DVDs. It's just a question of flagging it properly (set in the MPEG2 encoder).

The issue comes with mixing TFF and BFF footage. You can do this (DVDs accept it) if the MPEG stream is flagged correctly, but it's not a great idea - it's a pain to edit, and DVD players may display a visible glitch at the transition.

Cheers,
David.