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mpeg streamclip framerate conversion question

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dan freshman
mpeg streamclip framerate conversion question
on Aug 31, 2009 at 9:04:05 pm

I have a friend who, when going from 24p to any codec at 29.97, just changes the framerate in mpeg streamclip where you can enter any framerate into a box. I was wondering if anyone could say what's going on with the footage when this choice is made? How are frames added etc..

thanks
dan


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Daniel Low
Re: mpeg streamclip framerate conversion question
on Aug 31, 2009 at 9:44:19 pm

Nothing sophisticated, MPEG Streamclip is not a great transcoder, although it is a great tool.. Frames/Fields will be doubled and fudged rather than have any complex 'interpolation' or calculations applied

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Brian Alexander
Re: mpeg streamclip framerate conversion question
on Sep 1, 2009 at 12:47:23 am

Never tried it but I doubt that MPEG Streamclip does a Telecine process to the footage. I would bet that by default the clip is sped up.

If you're feeling up to it I would suggest creating a 24 fps video (or use your friend's footage) and add visible time code overlay by running it through Compressor. Then take the video with the overlay and do your 24fps to 29.97 fps and inspect the result frame by frame. If you do not see added frames then something else is going on.

You know...I think I could have done this faster by just doing it rather than thinking about the process and trying to explain how to do this...

I'll post my results shortly.

--
Brian Alexander
Sr Video Engineer
Freeman AVS


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Brian Alexander
Re: mpeg streamclip framerate conversion question
on Sep 1, 2009 at 2:05:13 am

Well, I only did a few seconds of progressive frames (which I'm guessing that's what you're working with) and here's what I've found:

MPEG Streamclip very simply, just duplicates frames.

24fps in a 29.97 count reveals the following duplicate frames:

3&4, 8&9, 13&14, 18&19, 23&24, 28&29...(I see a pattern!)

That was fun.

Now for the real question...What is friend trying to do with his video? Why is he trying to do this type of workflow? There are only a couple of reasons why he'd need to change the frame rate in this way.

Perhaps a couple of quick questions would reveal some concise help to his conundrum.

Thanks.

--
Brian Alexander
Sr Video Engineer
Freeman AVS


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dan freshman
Re: mpeg streamclip framerate conversion question
on Sep 1, 2009 at 2:11:50 pm

brian,

Thanks for doing that. After reading, I feel guilty for not doing it myself...my friend has been using it to replace adding pulldown and he is a guy who has fallin in love w/ mpeg streamclip. I think that I kind of agree; that for adding pulldown to 24p footage (as his media library as well as mine has to be conformed to 29.97) that duplicating frames seems better than a telecine process if material is going to be viewed on progressive monitors. would you disagree?

thanks again for you help,
dan


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