What are valid custom PAR values for MP4?

[SamKook]

I'm trying to keep the original AR of a video that I cropped by setting a custom PAR in mp4box, but it keeps crashing on me because of invalid values.

I want to encode it to either mod16 and then modify the PAR for the tiny difference that's left
or
leave the original resolution and set the PAR to get the right AR.

So I was wondering what defines a valid MP4 custom PAR? I tried looking for an answer in the specs, but there's so many information that it's not easy to find something specific and the terms I searched for left me with no answers so I was hoping someone here would know.

[Sharc]

I'm trying to keep the original AR of a video that I cropped by setting a custom PAR in mp4box,
You need not change the PAR just because you cropped the original picture. Changing the PAR will distort (stretch or squeeze) your picture.

I want to encode it to either mod16 ...
Any good reason why you want to go for mod16? Is the video going to be mpeg-2 encoded? No need to stick to mod 16 for AVC (mpeg-4).

...leave the original resolution and set the PAR to get the right AR.
PAR = DAR / SAR.
DAR (Display Aspect Ratio) is normally either 4:3 or 16:9 (or your AR)
SAR (storage aspect ratio) is your "original resolution"

So I was wondering what defines a valid MP4 custom PAR?
"Custom" PAR can basically be anything.
Standard PARs are 12:11, 16:11, 10:11, 40:33

You may also want to check this blog (http://blog.komeil.com/2006/09/modify-mp4-aspect-ratio-mp4box-mpeg4.html)

Difficult to give you better advice without a sample.

[SamKook]

I forgot to mention that the original video is squished and gets corrected with DAR, which is why I needed to set the PAR in the mp4.

The mod16 was just for possible extra compatibility(no idea if that actually change something for AVC) with crappy external media player and also because I already had those value calculated for an Xvid version(and it also fix the problem that I can't resize to odd values), but that's not my preferred option.

It is usually 4:3 or 16:9, but not anymore when you crop it more on one side than the other. I'm well aware of the PAR = DAR / SAR equation and my problem is not with finding the value I need which is why I didn't provide a sample.

So after saying all that, I tried it again this morning and any input value I used seem to work without any problem... I guess the "invalid entries may cause job to error out" message in the GUI made me think that was the problem and I now feel stupid for not have been doing more testing before asking this question here.
No idea why it wasn't working before though.

[Sharc]

Glad you solved the problem :)