Pixelated mxf clip from Clip Browser at DVinfo.net

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Old May 20th, 2009, 02:09 PM   #1
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Pixelated mxf clip from Clip Browser

Fortunately this was not any serious shot, but today I have witnessed an ugly pixelation artifact (lasting exactly 12 frames, which is PAL GOP length) after using Clip Browser to export straight to mxf from an SxS card (see grabs below; it can look either way depending on how it's viewed).

This hasn't originated in camera, as the original mp4 file is absolutely clean.

Has anyone encountered anything similar? Any ideas as to the reason?
Attached Thumbnails
Pixelated mxf clip from Clip Browser-mxf-glitch.jpg   Pixelated mxf clip from Clip Browser-mxf-glitch-2.jpg  

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Last edited by Piotr Wozniacki; May 21st, 2009 at 04:33 AM.
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Old May 20th, 2009, 02:18 PM   #2
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I have seen problems like that with Disc drive corruption.

Try transferring (from clipbrowser) to another disc.

And run a test on your disc.

I assume clip plays fine in the camera.
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Old May 20th, 2009, 02:27 PM   #3
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I agree this might point to the HDD (I saw similar effects on a clip, copied from the DR60 drive to a local HDD), but I scanned this one for errors and it's fine.

Also, another attempt of exporting the clip to the same drive produced fine results.

This is scary, as CRC only works during copying, and not rewrapping... In real life projects, it's impractical to inspect all mxf clips in their entirety, before deleting the originals from media!
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Old May 20th, 2009, 04:56 PM   #4
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CRC checking on?
Yes CRC only on copying.
If there was no problem there than it may only be issue with rewrap.
You can probably go back to the BPAV/MP4 and try rewrap again to another drive as recommended.

ALWAYS save BPAV as master. That's the point! The clip metadata ID doesn't change so you can just rewrap and replace if you come across a clip like that in your edit workflow.
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Old May 21st, 2009, 04:14 AM   #5
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Yeah, yeah - with real projects, I always save entire BPAV's, and in several CRC-ed copies, too. Using ShotPut for that. Blah blah.

This however was one of those quick test shots, so I went straight to exporting mxf...

This may serve as a valid memento to those treating the entire matter of media handling too lightly. However, I brought it up with yet another purpose in mind - namely, I'm seeking theories behind the mechanism of creating such glitch in the solid state media video...

Interestingly, in the original clip there is a loud noise when I accidentally bumped against the camera - and it happens EXACTLY simultaneously with the pixelation (see the grab from Vegas). This makes me wonder: could it be the reason? Some intermittent losing of contact in the SxS slot perhaps? Sounds unlikely, I know - but the coincidence makes me wonder...

On the other hand, as I said before, the pixelation is NOT visible in the original MP4 clip (nor is it present in any subsequent mxf exports from it) - so is the bump a pure coincidence? I guess I'm lacking a deep enough knowledge about digital imagery creation innards; if someone could come up with any suggestions - I'm all ears!
Attached Thumbnails
Pixelated mxf clip from Clip Browser-audio-bump-pixelation.jpg  
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Last edited by Piotr Wozniacki; May 21st, 2009 at 09:47 AM.
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Old May 21st, 2009, 08:40 AM   #6
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I'm hard pressed to dismiss the connection between bumping the camera and the problem. Given that this is one of the very rare reports of such a problem the probability of two such unlikely events occuring at the same time is extremely small. Then again apart from the bump stressing the codec as it tried to compress the video what could have happened and even then how were you later able to decode the clip without the error.

Or is this a Vegas 9 problem?
I've had issues with V8 where HDV recorded with high errors requiring the codec to perform serious error correction would slow V8 down to a crawl. Other issues of V8 crashing that I've witnessed were also very likely related to the amount of errors in the mpeg stream. I'd be interested to see if you went back to your problem clip again with V9 or V8 if you still see the problem, restarting Vegas may have been what cleared the problem, not tranferring it again.

I also find it hard to believe that the process of copying a file using any OS can have a significant risk of errors. The amount of data copied every day using Windows, OSX and any other OS is mind boggling and dwarfs the amount copied from SxS cards. If there was some inherent unreliability in the process, computers of every flavour would be crashing all around us, simply put, no one would be using them.
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Old May 21st, 2009, 09:10 AM   #7
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Bob, for God's sake - it looks like we're broadcasting at the very same wavelength (perhaps because we're both engineers)?

I also find the coincidence between bumping the camera and the video glitch hardly probable - in spite of the waveform and the picture coincidence in time.

Similarly, I believe the CRC is just a hype - for the exact reasons you mention (yet I still use it when copying to my archives of serious projects...).

But no, it's not a Vegas 9 problem - the glitch occured during the mxf export in Clip Browser, and is present when playing back in V8, V9, VLC... it's just there!

All in all, I'm tending to blame my card, or card reader, or HDD - or something happening in my OS while exporting.
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