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November 1st, 2009
Message text:
After Effects error: Zero denominator in ratio addition.
Message interpretation:
After Effects was unable to correlate two internal variables in a mathematically sensible way.
Possible causes:
There is a number of situations where this could occur, but essentially it always is caused by mixing materials with different resolutions and framerates. Often it is caused by wrongly set footage interpretations, where the pixel aspect ratio of a source material does not match the actual pixel data. This will throw an error, if e.g. anamorphic video material needs to be expanded to its square pixel equivalent. When using still images, odd sizes that do not present multiples of 2 in either dimension can cause problems.
A similar problem is, if the framerate of the footage is not set correctly, and the footage used in a composition wit ha different framerate. Most commonly affected is for instance footage actualyl recorded at the correct 29.97fps for NTSC, but being interpreted as 30fps. Since certain rounding errors will accumulate after a while, somewhere down the line the program may not be able to compensate for this mismatch. Recently this issue has also popped up more often with AVCHD and H.264 derivatives recorded from different digital video and photo cameras that use pa pulldown to mimic the appearance of 24fps film at different native framerates.
Likewise, compositions with different unusual framerates that are being nested might cause the same troubles. The use of audio in the project usually makes the problem more severe. Additionally, certain combinations of operations that spatially transform pixels (scaling, displacement) in combination with features like continuously rasterize/ collapse transformations have been known to give the error.
Resolution or workaround
If you are using unusual source footage resolutions, modify your composition or footage, if possible. Cropping or resizing an image in Photoshop can make all the difference. In After Effects, make sure your footage interpretations meet the facts. Check your camera manual for the correct specifications. Set your composition settings so, that nested compositions have either the same framerates or even multiples/ fractions of the main framerate. E.g. in a 30fps scenario, an 11fps sub-comp might be problematic, since it has a remainder with any division operation, as both elements do not share a common divisor, but 12fps might work perfectly, since 30 and 12 can both be divided by 6. if unsure where things go wrong, isolate the problem by selectively toggling switches nad adjusting values.