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AVCHD 24p fps

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Jason Schoenfeld
AVCHD 24p fps
on Sep 30, 2011 at 4:57:19 pm

I recently shot some video on a Canon HG10 at (what I thought) was 24p fps - just to try it out. When bringing the original .MTS files into After Effects and I go to 'Interpret Footage' it shows the video as being 30 (29.97) fps. In the past I've only worked with 30 and didn't really need to necessarily worry about the frame rate. So, I'm confused. Is After Effects just interpreting the video incorrectly, or am I really not taping at true 24 fps?

Any help would be appreciated.


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ben g unguren
Re: AVCHD 24p fps
on Sep 30, 2011 at 6:20:06 pm

You're probably shooting at 30. I imagine AE can get this wrong, but it isn't likely. If you want to check, interpret the footage (right click, interpret footage-->main...) as 24 and then ram preview it. If it's slow motion, then you shot at 30.

You could also try opening the clip in other apps, like MPEG Streamclip or VLC and see how those report the fps for the footage. (Kind of like going to another doctor for a second opinion.)

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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Kevin Camp
Re: AVCHD 24p fps
on Sep 30, 2011 at 6:27:58 pm

it's possible that the codec does not contain frame rate data, or ae isn't seeing that data. in cases like that ae relies on a set of predetermined rules that may no be correct.

double click the footage in the project window, then step through the footage frame by frame (using arrow keys) and see if there are any interlaced frames.

if you are finding interlaced frames, then the footage may be shot 24p but recorded with a pulldown add (making it 29.97).

if that's the case, ae can remove the pulldown and make it true 24p by setting ae to separate fields (i assume you shot 1080, so upper field first) and choose the pulldown cadence to remove, or click 'guess cadence'.

if you see interlaced frames on every frame, then it was shot at 30i... if you see only progressive frames, then it was shot 30p...

if you happen to see no interlacing, but see a duplicate frame every 5th frame, then it was shot 24p, but recorded 30p. to get rid of the duplicate, leave the footage as 29.97 (don't separate fields) and drop it into a 23.976fps comp and you should be fine.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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Jason Schoenfeld
Re: AVCHD 24p fps
on Sep 30, 2011 at 6:42:42 pm

Thanks Ben and Kevin. I've gone through the video and there's no interlacing at all. I'll check to see if there are duplicate frames every 5th frame. Also, what is meant by "shot 24p, but recorded 30p?"


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ben g unguren
Re: AVCHD 24p fps
on Sep 30, 2011 at 7:22:49 pm

I am not familiar with your particular camera, but many medium-to-high-end cameras allow you to choose the rate you film at AND the rate you encode at. In most cases you'll want these to be the same, but it's possible to have them be different. You'd have to check if this is a possibility on your camera.

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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Kevin Camp
Re: AVCHD 24p fps
on Sep 30, 2011 at 7:33:45 pm

when video cameras started shooting 24p, they still had to record to tape which had to be 29.97 for ntsc, so the camera would have to add a pulldown to record. for sd formats, that meant the typical progressive frame-interlaced frame cadence, but for hd (particularly 720) it meant recording duplicate frames.

that continued even with shooting to files rather than tape... ex: the older panasonic hvx had a setting to recored 24p native, which meant 24 fps without the duplicate frames -- though i have no idea why anybody would have chosen to record duplicate frames -- but different cameras do different things, so it could be possible that your camera records 24p as 30p... but i really don't know.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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Jason Schoenfeld
Re: AVCHD 24p fps
on Sep 30, 2011 at 8:06:38 pm

Thanks again for the help. I'll have to check my camera and see if it encoded it as 30 or see if there is an additional setting that I need to set or if it just records 24 as 30. It's an older Canon (HG10) and it does a very good job although I've had some difficulties with the AVCHD codec and FCE.


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Jason Schoenfeld
Re: AVCHD 24p fps
on Oct 1, 2011 at 12:59:44 am

Got home and checked the video on VLC and it does show as 60i and it very much looks interlaced in VLC. So, AE was interpreting correctly.

On a side note, in VLC it also shows the size as being as 1440 x 1080 (doesn't show aspect ratio). However, when I drag it to make a new comp in AE it creates a preset comp of 'HDV 1080 29.97 (1440 x 1080)' with a pixel aspect ratio of 'HDV 1080/DVCPRO HD 720 (1.33),' but the video looks squished and looks 4:3. If I manually change the comp to 1920x1080 with square pixels aspect ratio it fits and looks great. So, again I'm confused. Is it 1440 or 1920? I mostly just work with 720 so it hasn't been that big of an issue (I just drag it in and fit to comp...looks great). Just gets confusing.


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Jason Schoenfeld
Re: AVCHD 24p fps
on Oct 1, 2011 at 3:14:14 am

Figured out the video aspect ratio. Just clicked the 'Pixel Aspect Ratio Correction' button and fixed it.


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