QTGMC frame rate question

[jedson]

I'm using the latest version of Hybrid for Mac and have a general question about deinterlacing NTSC video with QTGMC.

Assuming I want to keep the frame rate of 29.97, how do I decide whether to select "even" or "odd" if "bob" is deselected?  Is there a setting in the input file that would indicate which one should be used?

Thanks!

[Selur]

Assuming your input is interlaced NTSC and not telecined, it should either be signaling tff or bff.
Hybrid does show the detected input scan type on the Base-tab and under "Filtering->(De-)Interlace/Telecine->Deinterlace/Telecine Settings->Input scan type".
If your source is interlaced and you deinterlace to same frame-rate thus throw away half the fields it doesn't really matter.
Usually I would recommend looking comparing the preview for both, since especially for old content, sometimes one field is better quality than the other.
If your source is NTSC telecined, you should not use QTGMC, but for example TIVTC (you can use QTGMC in it for the deinterlacing of residual combed fields).

Cu Selur

[jedson]

It is NTSC interlaced video, not telecine.  I'll make tests and compare.

Thanks!

[jedson]

Here's a follow up question:

If interlaced video is not being detected -- the scan type is showing up as progressive in both Hybrid and MediaInfo -- is there a way to tell whether the source video is tff or bff?

The source is interlaced NTSC standard VHS captured on an older Macbook with ezcap.  Nothing high def about any of this setup.  I'm just using the tools at my disposal to get a decent encode for sharing on a private tracker which has minimum quality requirements.

[Selur]

.. is there a way to tell whether the source video is tff or bff?

Sure, read: [INFO] Interlacing patterns.

What you would basically do, is:
a. overwrite the scan type to bff or tff
b. enable QTGMC in Bob mode
c. look at the output in the Vapoursynth Preview.
When you can move through the frame and the motion is fluid (in a scene with horizontal motion), the frame type you selected is correct, if you see forward and backward movement, you need to overwrite to the other scan type.

Cu Selur

[jedson]

Perfect, thanks.

I did look at the info thread, btw, but for some reason I got confused.  Maybe not yet sufficiently caffeinated.