VHS capture having incorrect CHROMA field order.

[useraxe]

I'm having a weird issue with my captures, where the colors look like they have incorrect field order, but the luminance channel is fine. Example - deinterlace a regular video with incorrect field order, though the problem will be on both Y & C.

Is there any way of fixing this through Avisynth? (I spent hours finding a script, but it only caused a headache).

And this has been an issue with 2 VCRs and 3 capture devices, I have no idea what causes it.

[jagabo]

You should post a sample that clearly shows the problem. I doubt the problems is really the chroma channels being the wrong field order. But if that's really the case it could easily be fixed in AviSynth.

[useraxe]

I hope a GIF is ok.

[jagabo]

A GIF is not a great way to show the problem because the video is converted from interlaced YUV to progressive RGB. Many errors can occur from that conversion. That's why it's important to have the original cap. Or use a program like AviDemux or VirtualDub to COPY (remux) a section of the video to a new file. In VirtualDub use Video -> Direct Stream Copy mode. In AviDemux set the video mode to COPY.

[useraxe]

I sent it to you in a PM.

[The_Doman]

I sent it to you in a PM.

It's that sensitive?

[useraxe]

CR material.

[jagabo]

You are right, the chroma has the opposite field order from the luma. I've never seen that before. Here's a fix:

LWLibavVideoSource("Sample.mkv", cache=false, prefer_hw=2) 
AssumeTFF()
SeparateFields()

swapped = SelectEvery(2,1,0) # a video with the field order swapped
MergeChroma(last, swapped) # use the original video for the luma, the swapped video for the chroma

Weave() # weave the fields back into frames.
QTGMC() # deinterlace for display

[useraxe]

Thank you, thank you! Looks excellent now.

[jagabo]

Here's something a little simpler:

LWLibavVideoSource("Sample.mkv", cache=false, prefer_hw=2) 
MergeChroma(AssumeTFF().SeparateFields(), AssumeBFF().SeparateFields())
Weave()
QTGMC()

The result is exactly the same.

[johnmeyer]

jagabo: very nifty fix.