Pixel Aspect Ratio – When 720×480 = 853×480

I recently taught a couple of seminars in Los Angeles at StreamingMedia West. You can find links to the presentations at the link in the previous sentance.

I just got an email from a student asking:

At Streaming Media West you introduced the session to MediaInfo, a very handy tool, thank you. Quick question, on one video I notice that OSX “get info” gives me a different dimension than Media info does.  And a screen shot shows that it is 853×480 Do you know why that might be?

Here’s the pic, with OSX on the left, MediaInfo on the right. 

mediainfoosx.jpg

Here’s my response.

Let me tell you what I know, and you can tell me if it’s relevant – if you send me a short file I could confirm.

If this was a 16:9 DV file (I know it’s not), the true pixel resolution – or the actual pixels stored in the file — would be 720×480 – that’s what DV is. When displayed, though, because the pixels are stored at a pixel aspect ratio of 1.2 – you multiply the horizontal resolution by 1.2 to get the actual pixels the video consumes onscreen. 1.2 x 720 is 864, which for some reason, gets rounded down to 853.

It’s a very confusing area because of how the different products analyze and present the analysis. Bottom line is that there are 720×480 pixels in the file, but when displayed, it’s 853×480.

Here’s the response back:

Ok so another one of those square pixel, rectangular pixel situations.  Ok I just got my head around that with illustrator and titling/overlays. Thanks, appreciate the quick reply.

Which is exactly correct.

 

 

 

 

 

 

 

 

 

 

About Jan Ozer

I help companies train new technical hires in streaming media-related positions; I also help companies optimize their codec selections and encoding stacks, and evaluate new encoders and codecs.

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