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Old January 12th, 2010, 02:10 PM   #1
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'Wobbling' letterboxed images - help!

Hi All,

I use FCP on a MacBook Pro and am working on an SD project (720x576 50i PAL). When I convert HDV footage to SD 4.3 letterboxed the images look OK but 'wobble' slightly (and enough to notice) in FCP and this is especially noticeable on static shots and at the edges of the image. This problem remains when I make a DVD. I've tried de-interlacing too but this doesn't help. I let the sequence set the settings automatically when placing the clip in the timeline and all the settings are normal for an SD project.

Got a deadline to meet for Friday so if anyone can help I'd be very grateful.

Geoff
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Old January 12th, 2010, 02:28 PM   #2
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A bit more info please. You're shooting 16:9 HDV footage in what - a Z1? You're down-converting in camera and outputting it 4:3? The images are rock-solid at this stage? Have you tried keeping it 16:9 SD to see if that removes the wobble? Have you played the avi file on the computer to see if the NLE is introducing the instability?
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Old January 12th, 2010, 02:40 PM   #3
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Hi Tom,

Shot with an XH-A1. down converting done in QT after importing. No problem with the image until the letterboxed image is brought into FCP (plays OK in QT) and I think I've isolated it to the output - I use a Matrox MXO Mini; when I output via DVI the wobble disappears. However, and here's the weird part, when I burn a DVD (done via Compressor and FCS - no problems with this in the past) and play back via a projector the wobble returns! Some clips are native SD and these play back fine too so I'm very confused. Trying to render a version with the MXO output turned off but hard to see why this would help!
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Old January 12th, 2010, 02:48 PM   #4
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All very strange. I'd be tempted to downconvert in camera and simply work on an SD project. I'd keep it pillarboxed 16:9 though so projectors and screens don't get confused.
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Old January 12th, 2010, 02:56 PM   #5
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Good advice but unfortunately its all too late for that. It may be that certain output devices just don't like the images! When I play back the raw m2v file for instance on my LCD monitor or the computer screen it is smooth and solid so unless something is happening when I burn the DVD logic dictates it must be the playback device / output.

We soldier on....
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Old January 12th, 2010, 09:18 PM   #6
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The "wobbling" needs to be more defined as it can describe several type of image problems.

Also, what are your timeline settings in FCP? Do you have motion estimation set to "best"?

If possible can you post a 5-second clip of a wobbly segment?

Something seems amiss in your workflow but more info is needed to drill down to the culprit.
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Old January 13th, 2010, 03:35 AM   #7
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Hi Robert,

Settings as follows:DV PAL 720x576 CCIR 601 (5:4) - same for PAR
Field: Lower
Compressor DV PAL 100% quality
Motion Estimation: Best

All as one would expect I think.

The wobble is a kind of vertical shimmering most obvious at the bottom of the frame (letterbox) where the image seems to bleed into the black of the screen in a rapid and distracting shaking. This has nothing to do with motion on the screen as the images are almost completely static. No point in posting a clip as when rendered to QT the problem disappears but returns when DVD played via a projector (not on my LCD TV!).

Could lowering the data rate of the DVD in Compressor help perhaps - I use 6.8 average rate?
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Old January 13th, 2010, 04:03 AM   #8
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Changing the MPEG2 bit rate won't help. You more accurate description sounds very much like line 'twitter' that was very obvious in CRT days. Fonts with a one line horizontal constituent would flicker on and off as the 50 Hz fields replaced one another.

Shuch fonts are best avoided with any video (rather than film) medium. I wonder if that's what you're seeing at the letterbox / picture interface?

tom.
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Old January 13th, 2010, 04:47 AM   #9
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Interesting Tom but as you mention fonts that suggests text and these are images which I can't really alter in any way 'fontwise'...
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Old January 13th, 2010, 08:39 AM   #10
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The motion estimation tab I'm referring to is in the FCP timeline, not Compressor. I don't think the issue has anything to do with compressor, it's either in the footage or some mismatch in timeline settings.

Without seeing a clip I don't see how anyone can really offer any further advice; it's all guesswork otherwise.
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Old January 13th, 2010, 09:50 AM   #11
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Robert,

Sorry my confusing response - the compressor setting here IS the setting in FCP as is the motion estimation.

You are right of course about a clip but as it seems to be an output problem then a clip isn't helpful as in QT it is fine; I was just hoping someone else who uses the MXO (or has noticed similar problems with DVD projection) might have recognised the problem.

Thanks for your thoughts anyway.
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Old January 13th, 2010, 10:01 AM   #12
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Hasn't there been countless reports of HDV looking horrible when down converted to SD? You might want to try a quick search on these boards. Your problem may be with the interlacing. Is your original HDV interlaced or progressive? If it was already interlaced (HD is upper), introducing the SD interlacing and then de-interlacing that SD footage as you mentioned wouldn't help. If you are progressive, then your sequence settings should have the field set to none. I know DVDs are interlaced anyway, but this has given me better quality encodes in the past. I think working with interlaced footage is a mess, unless you are only doing simple straight forward cuts. No effects and no down converting.
I have seen vertical banding/warping before on HDV footage, but in my case it was only in FCP, not on the footage.
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Old January 13th, 2010, 05:48 PM   #13
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the "wobble" effect comes from interlacing. It's most noticeable in stills with hard edges. Since the letter box has a hard edge you will notice it there as the odd and even fields alternate. To diminish this effect a de-interlace filter can be applied to a still image, for a letter box you could try an edge blur since you don't want to soften the entire image.
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Old January 13th, 2010, 06:18 PM   #14
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Have you tried importing the HDV footage directly into the SD project? This sort of shimmer occurs when the horizontal line of the letterbox is not sitting directly on a scan line, it's between lines. FCP does this when I drop PAL footage directly on a NTSC timeline and the 576 lines get crudely mashed into 480 lines. A good standards converter fixes that.

Like another poster suggested, I would try making 16:9 SD files first if you want to transcode before importing.
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