Cannot encode due to aspect ratio 'not divisable by 16' status??

[ptfigg]

Can someone clarify why I cannot encode proprietary aspect ratios? For example, I want to size a 720x480 movie to 360x240. ffmpegX will not allow due to the 'width not being divisable by 16', so it says ...

Thanks.

-ptfigg.

[rumplestiltskin]

You must respect the "rule of 16's" so 352x240 would be a "legal" size.

What I do is divide the desired width (using the 16's rule) by the original width; then multiply the result by the original height. Round that up or down to a multiple of 16 and you're good to go.

There are other tools that will permit any size you wish but due to the size of the "macroblocks" (as I understand it), it is always best to use multiples of 16 to maximize quality.

I realize this isn't a complete explanation but others who have a greater understanding of the underlying technology will be sure to chime in.

[ptfigg]

Thank you and understood ...

I'm clear on the scentifics.

-ptfigg.