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Weird Glitches on Encoded Clip

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John Dobovan
Weird Glitches on Encoded Clip
on Feb 15, 2011 at 2:31:22 am

Hi:

I'm editing with FCP 6.06 on a Mac Pro Intel dual 2.66. I've got a 1-hr HD video project that I'm trying to encode as a Standard Def DVD. I've output the 720 p30 master as a standalone QT file and used the standard settings in Compressor (90 min. Best Quality) just as I always do. But the playback has a very strange breakup in various places. The subject matter is pretty simple - just a guy on a beach doing yoga. Yet every now and then the picture degrades, looking almost like the old days when tape playback would lose horizontal sync and cause a glitch. It lasts several seconds and then fades away.

I should add that the same spot in the exported master clip is very clean and beautiful, this only happens on the compressed video file. I've tried raising the data rates and that helps a lot but I'm now up to 6.8 MBPS average and 8.0 max, which I believe is the maximum allowable for most DVD players. It's much better than it was on the presets but still has some problems.

Can anybody verify the max rates for SD DVD? And maybe suggest an alternative compressor?

Thanks,
John D.


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Jeff Greenberg
Re: Weird Glitches on Encoded Clip
on Feb 16, 2011 at 6:27:08 am

Instead of an alternate compressor, let's try a workaround.

Could you downconvert it first into uncompressed and THEN make your MPEG-2? If it works, i'll tell you why it did.

Best,

Jeff G

Apple Master Trainer
Avid Cert. Instructor DS/MC
Avid & Color Videos Vasst.com
Compressor Essentials Lynda.com


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John Dobovan
Re: Weird Glitches on Encoded Clip
on Feb 16, 2011 at 6:30:41 am

Jeff:

I'll try anything. But just to be sure I understand, are you saying use Compressor to convert the original file to uncompressed? I think I can also output it from FCP at something close to uncompressed.

Any and all suggestions gratefully accepted...

J.



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Jeff Greenberg
Re: Weird Glitches on Encoded Clip
on Feb 16, 2011 at 6:33:26 am

I'm saying do the downconvert from 720 to an uncompressed SD file.

THEN give that back to compressor to make a DVD/mpeg-2

I suspect that there's a bad gop pattern in your original footage and it's causing problem during the downconvert/compress, which I'm putting into two separate jobs.

Best,

Jeff G

Apple Master Trainer
Avid Cert. Instructor DS/MC
Avid & Color Videos Vasst.com
Compressor Essentials Lynda.com


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John Dobovan
Re: Weird Glitches on Encoded Clip
on Feb 16, 2011 at 6:39:23 am

OK, that sounds like a good idea, I'll run it now and report back here. Many thanks Jeff!



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John Dobovan
Re: Weird Glitches on Encoded Clip
on Feb 16, 2011 at 8:51:52 pm

Hmm. Stil the same problem. But I see that I've introduced a new problem in the aspect ratio during the down convert. And the resulting file won't play back properly off this FW drive I have it on. I'll have to try this again from a faster drive.



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John Dobovan
Re: Weird Glitches on Encoded Clip
on Feb 17, 2011 at 1:00:48 am

Weird. That's actually worse now. Just to be sure I'm doing this right: I exported a standalone 720p30 file from FCP, then encoded that in Compressor as an uncompressed 10-bit 16x9 SD video clip. And then used Compressor again to encode for DVD at the hightest rate. When that failed, I bumped the data rates to 6.8/8.0. Still, some very bad artifacts now.

Interestingly, the original HD clip was only 26 GB but the SD encode came in at 100GB. Obviously, the HD wasn't a completely standalone file.

I'm going to try exporting from FCP again, this time as an uncompressed SD file direct to a faster drive and see what happens.



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Jeff Greenberg
Re: Weird Glitches on Encoded Clip
on Feb 17, 2011 at 12:33:38 pm

John,

I was just using a brute force method - you're downscaling and compressing. I was trying to separate the two steps.
Uncompressed footage really won't play back unless you have very fast drives. Since this still had problems, you can abandon this method.

Before you do - does the uncompressed SD file have the same problems in the same (or similar) places as your original compression?) If so, some of your media may be corrupt.

Ok, plan b (c? d?) Just export the sequence DIRECTLY to compressor - skip making the QuickTime file.

Again, the glitches - are they still there?

If I'm a little slow to respond, it's because I'm at a conference.

Best,

Jeff G

Apple Master Trainer
Avid Cert. Instructor DS/MC
Avid & Color Videos Vasst.com
Compressor Essentials Lynda.com


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John Dobovan
Re: Weird Glitches on Encoded Clip
on Feb 20, 2011 at 1:02:04 am

Jeff:

No, the original material looks fine. It's just the encoded versions that look bad. Tried exporting directly to compressor but that failed to even work. I'm starting to think this may be drive-related. I have the entire project on a 1TB FW drive, connected via FW400. The project was shot and cut at the low end of 720p30 (960). Even so, it tends to stutter or freeze on playback. So I'm thinking I need to port the whole thing over to a faster drive and try again. Unless you have a better idea.

thanks for your help,
John



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Jeff Greenberg
Re: Weird Glitches on Encoded Clip
on Feb 20, 2011 at 7:33:50 am

John,

[John Dobovan] "Tried exporting directly to compressor but that failed to even work"
This might be a red flag. What's wrong with your system that exporting to compressor doesn't work?

On your instinct over the drive: Let's rule out the drive then. export a QuickTime to that drive and see if it as has a compression problem.

Hell, after that, try compressing a one or two minute section that's challenging and see if it works.

Best,

Jeff G

Apple Master Trainer
Avid Cert. Instructor DS/MC
Avid & Color Videos Vasst.com
Compressor Essentials Lynda.com


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John Dobovan
Re: Weird Glitches on Encoded Clip
on Apr 2, 2011 at 5:06:20 am

Jeff:

This project file is unlike any I have ever experienced before. I shot in HD (albeit 960x720 on a Panny 170) and edited to 1280x720. It was basically a single take of about an hour duration. The FCP edited video looks great on my HD monitor and when I export the file, in either SD or HD, it looks great then too (Iʻve tried exporting both by reference and as a stand alone file). But when I compress it using the same settings I have always used in Compressor, I get a pattern of glitches that come and go on a regular basis. Not constantly but persistently enough to make the end product unusable. I have compressed numerous other files before and since with nothing like this, ever. Been in this biz since ʻ75 and nonlinear since ʻ90 so I donʻt think Iʻm making any newbie mistake here. But Iʻm at the point where I am either going to have to refund the client or re-shoot. But before I do that Iʻd like to try sending the file out for compression by somebody who knows a whole lot more about compression than I do. Is this something you could/would handle? Or can you recommend somebody?

Thanks,
John



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