DVD Interlaced field comb effect. Now you see it, now you don't?

Yes I can see the combing on any format on my iMac.

As I said, only the DV-PAL encoded in iDVD shows it.

I've been wondering whether it has anything to do with the fact that the 576 lines are being upscaled to 1080, thus doubling their size and making them more visible. (But why doesn't it happen with DVDSP?)

Conversely, when a hi-def project is reduced to standard def, the 1080 lines are squashed down and it may be that they become so fine they just blur out.

Just to throw one more variable into the mix . . . . I have a WD TV HD media player also connected to my Sony TV.

When this is fed with interlaced .mp4 or .mov encoded with H.264 the results show interlacing on both hi and standard-def videos.

The 1920x1080 encoded ones play OK but when frozen the field lines are obvious.

The 720x576 ones show the field lines even when playing.

All very strange.

Something even weirder has just happened!

When I said I could see the lines on the Mac I was referring to seeing them in FCP X when "Show both fields" is selected, so I popped a couple of DVDs in to play on DVD Player . . . . one originally AVCHD and the other DV-PAL.

When I clicked on various parts of the timeline, each DVD showed severe combing on action shots.

Wanting to double-check, I put the first DVD back in and I tell you no lies . . . . the combing had disappeared, being replaced by a general blurring a la Progressive!

The same phenomenon occurred when I re-tested the second DVD!

It's almost as though the Mac had deliberately started deinterlacing to make me a liar!

Retesting DVDs etc. on the TV has not altered any of the findings, thank goodeness.

I think I may have solved that final weird problem that I noticed when replying to you.

Namely why the Mac's DVD Player displayed interlaced frames and then didn't.

DVD Player had "View>Enable Deinterlacing" selected.

I imagine that when I froze a frame, it displayed it as interlaced because the deinterlacing algorithm only works during video play, not pause.

However, when I moved the video with the frame advance, it realised the video was on the go and stepped into action.

Unfortunately this doesn't help to answer the original puzzling questions.

I have been testing with FCP 7 and FCP X which bear little resemblance to the various iMovies.

The DV and HDV have been used both natively and exported as H.264 but however it's done the results seem the same.

Incidentally, I started using iDVD again last year with AVCHD (exported as H.264 from FCP X) and to my surprise found that it gave perfect results with no judder like the HDV stuff I experienced back in 2008.

I then tested some of the original HDV footage that had caused the problem and could not reproduce the judder! The HDV was exported as 1920x1080 H.264.

I think the instability was caused by my workflow.

HDV of course is widescreen but iDVD can only recognise HDV as widescreen when it is in AIC format.

As I was using mainly FCP 6 (at that time) which handles HDV natively I was not converting it to anything else.

So I think that iDVD was producing 4:3 video which my TV/DVD player was stretching to 1366x768 (which was the pixel size of my 32" Panasonic TV.

I belive this upscaling and stretching may have been responsible for the jitter.

Anyway as it no longer occurs I think it's best forgotten.😉