aspect ratio specification?

[shun]

When you make a video using say VirtualDub and x264, how do you specify what the playback aspect ratio should be, despite the pixel dimensions? For example HDV is 1440x1080 but is viewed at 16:9

[poisondeathray]

you add the command to the custom command line box , sample aspect ratio (SAR) . Think of it as the shape of pixels

--sar x:y

where x is the width , y is the height of pixels

For 1440x1080 you would enter --sar 4:3 , because 16/9 = 1440/1080 x 4/3

[Cornucopia]

In general, you DON'T specify DAR or PAR in an AVI container itself (although it's possible, but not many apps/players recognize it anyway). Where you would specify it would be at the codec level. Many codecs don't support DAR or PAR, but some do (DV, MPEG1/MPEG2/MPEG4/DivX/h.264). Even then, player recognition & support is spotty.
Note that I didn't mention SAR (storage aspect ratio). That's because it doesn't really exist. It's just shorthand for Horizontal Resolution divided by Vertical Resolution, but you don't really NEED shorthand for that. If "SAR" is referring to "Sample" aspect ratio, this is the same as Pixel Aspect Ratio (PAR, the accepted term).

Virtualdub itself doesn't affect AR of any kind, although you can adjust the preview of Input or Output by right-clicking the respective preview window. In the codec dialog box(es) is where you can set the AR. The implementation of the codec will determine where in the dialog the choice is given, if at all.

HDV, like mentioned above, is a 16:9 DAR, but a PAR of 4:3 (and consequently an SAR also of 4:3).

Scott