Not all codecs allow arbitrary frame sizes; many use blocks of a certain size (for example, 8×8) and require that your video frame be an even multiple of the block size.
You could export a lossless AVI from AE and try one of Microsoft’s free encoders; alternately, you might letterbox or pillarbox your output for client review purposes into a standard frame size.
The COW also has a Compression techniques forum, where you might be able to find some help.
Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
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