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Mystery of different but the same pixel aspect ratios???
I posted this in the Final Cut Forum but copied it here since it is as much an AE question as a FCP question.
Mystery here? I have digitized multiple shots off of the same DVC Pro tape into FCP. All of these shots have been captured the same way at 720×486 with a Pixel Aspect of “NTSC-CCIR 601”. In Final Cut all of these clips look and play great. When I import these quick time clips out of my capture scratch file and into After Effects certain clips list their aspect ratio as 0.91 and others are 1.00. The 1.00 clips are wider than my normal D1 After Effects composition and look stretched wide.
Why is it that Final cut is telling me that the Pixel aspect ratios for these clips are all the same when After Effects is telling me otherwise? Why would they be different in the first place if I used the same capture settings and took them off of the same tape into FCP? Is there some sort of hidden Meta Data that FCP reads on DVC Pro Tapes that can detect different cameras pixel ratios and then compensates for them when it brings it into FCP (these shots on this 1 tape came from multiple cameras all around the world)?
My basic question is why does After Effects read a different aspect ratio for the exact same video clip as Final Cut?
Thanks to those of you willing to tackle this mystery? I have been really aggravated with all of these new fangled aspect ratios floating around that are not consistent from one program to another!
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7 Replies
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Thanks Dave. In the years that I have ben capturing DVC Pro Tape at 720×486 it has not given me any trouble and the few black lines at the top and bottom have never been a concern. The bigger issue for me is why AE will correctly interpret most of my footage as non square (.91) but sometimes it will interpret it incorrectly as square pixel (1.00) aspect ratio when the capture settings/codec used to capture these clips were all set the same in FCP? These clips appear identical within FCP but once inside AE they change?
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Is there a difference in the number of pixels (height or width) in the clips that are interpreted as 1.00, compared with the ones that are interpreted as 0.91?
After Effects uses the frame dimensions to make a guess about what pixel aspect ratio to use when interpreting the footage. If it guessed wrong, you can correct it in the Interpret Footage dialog box.
See “Interpret footage” and “Pixel aspect ratios”.
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Nope, they are all 720×486. That is the great mystery to me, all of the settings are exactly the same for these clips but AE is incorrectly guessing some of them as square pixels. I know I can change this under “Interpret footage” but I am curious as to why AE is guessing wrong on some of these when they seem to be identical (captured with same settings off of the same tape).
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You mentioned that even though it was the same tape it was used in different cameras in different places around the world. You can record different pixel aspect ratios on the same tape, perhaps they’re not all quite as identical as they appear.
Just a guess.
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Yes they were shot on different cameras in different places but they were all dubbed down to the 1 tape I have now. I also ran a test of footage all from the same camera and tape and found this problem still persists which should eliminate the theory that different source pixel aspect ratios are causing this. Thanks for the input though! I suspect that this may just be an under the hood quirk of AE and am curious if anyone else has experienced it?
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Dave I believe you’re correct. Like DV 25, DV50 can ONLY be 720×480. Digitizing or interpreting or rendering it as anything but will likely cause issues. There are a couple ways that a program can determine the pixel aspect. By the codec such as DV or DV50 which has only one appropriate pixel ratio. And another is by the guess from the dimensions. So if a file IS actually somehow the DV50 codec but in a 720×486 wrapper then FCP or AE or both are going to get confused.
So, if it’s possible that the DV50 codec does support 486 it SHOULD be adding black lines at top and bottom. But perhaps AE is sometimes seeing the codec and sometimes seeing the dimensions and just giving a best guess on an inconsistent basis.
The solution is to simply highlight your footage and change the interpretation to the correct one, which, if your footage has the added black lines, should be the standard CCIR 486, not the DV.
Is the footage coming in Firewire to DV50? Or via AJA or matrox. Because if it’s on a DVCPro tape, then it definitely exists on the tape as 720×480. The DVCPro format is 480. There is no SD DV format that is 486. Well, there’s only two DV25 and DV50.
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Thanks for the input. I ran a test and recaptured some of the clips at 720×480 (instead of 486) that AE was reading incorrectly as square pixels. Turns out AE read the 720×480 footage just fine (non square) this time. But then to test it further I recaptured this clip a third time using the original 720×486 setting and AE read it correctly for some reason this time as well??? This at least blows the theory that there was some sort of hidden meta data in the original video off the tape telling it to display as square pixel.
Not sure if AE will always read my 480 footage correctly or not now? I plan to test this more extensively (and will post my findings) but until then it is my theory that the 720×480 vs. 720×486 issue is irrelevant and AE is just behaving quirky by reading random clips incorrectly as non-square pixel even though they have the exact same attributes as other correctly read clips.
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