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Deinterlace Question

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Tom Mooney
Deinterlace Question
on Aug 27, 2009 at 10:07:03 pm

I have been running tests for a project using the Flip for Mac WMV export program and I am not sure whether we need to deinterlace the footage. The original footage is shot 720p 30 and digitized into FCP using Apple Pro Res. The timeline has the field dominance set to none and it plays back fine. I have rendered test file out of Compressor with deinterlacing turned off and on. I cannot see much difference unless their is allot of movement in the shot. The footage that is not deinterlanced looks a bit steppy. When I compare frames of both movies it appears that the footage that was not deinterlaced looks sharper. The output movies are at 2400kbits, 1280 x 720. Is this just a subjective decision? Most of the footage has very little movement and practically no zooming.


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Craig Seeman
Re: Deinterlace Question
on Aug 27, 2009 at 10:19:41 pm

You should not deinterlace clips that are progressive.
Export out of FCP using Sequence settings Self contained.
In Compressor look at the clip's A/V Attributes and look for it's reported Field Dominance.



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Tom Mooney
Re: Deinterlace Question
on Aug 28, 2009 at 12:38:17 am

Files were not exported self contained. Will switch to self contained. Thanks you.



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Brian Alexander
Re: Deinterlace Question
on Aug 31, 2009 at 12:31:58 am

[Tom Mooney] "I am not sure whether we need to deinterlace the footage."
If this footage is really 720p then there will be no need to deinterlace because the footage is already deinterlaced, a.k.a., progressive.


[Tom Mooney] "The original footage is shot 720p 30 and digitized into FCP using Apple Pro Res."
Are you sure? What was the source shot/recorded with? Most 720p sources are 720p/60 (59.94). How did you digitize it into FCP? What equipment was used?


[Tom Mooney] "The timeline has the field dominance set to none and it plays back fine."
Even an interlaced source will look fine unless viewed at 100%. I would open the clip up in QuickTime for a true representation of the media. Look at the Movie Inspector in QuickTime for Codec, Bit Rate, and Frame Rate information. Always view your video at 100% for a true representation of your quality. Scaling up or down with monitors (even your laptop monitor) will introduce sampling errors and making your video look different than it actually is.


[Tom Mooney] "I cannot see much difference unless their is allot of movement in the shot."
Do you mean that there is interlaced artifacts in your movement? You shouldn't see any difference unless the encoder is doing a terrible job at trying to deinterlace a progressive frame.


[Tom Mooney] "The footage that is not deinterlanced looks a bit steppy."
Was this media created at a different resolution then given to you as 720p? Sounds like whatever did the original deinterlacing did not do a good job or you are not viewing at 100%.


[Tom Mooney] "When I compare frames of both movies it appears that the footage that was not deinterlaced looks sharper."
Sounds like the encoder is deinterlacing something. Usually a loss in sharpness comes from deinterlacing by blending the frames together. Again, I'd look at the original footage in QuickTime.


[Tom Mooney] "The output movies are at 2400kbits, 1280 x 720. Is this just a subjective decision?"
This seems a bit low for a visually lossless output but that all depends on which codec you are using. Even with talking head, I usually allocate 5 - 6 Mbps if using QuickTimes H.264 codec. 2400 Kb sounds about right if using CompressHD or the X.264 codec. If you are seeing Macroblocks on your encoded file you may need to bump the bit rate or lower your frame size. I base all of my output settings on Visually Lossless encoding.

Do you have any screenshots or clips to share with us? A small sample of the source footage would be great.


--
Brian Alexander
Sr Video Engineer
Freeman AVS


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