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I'm trying to setup my site to store uploaded user content in a 640x360 frame size, which will be presented back for viewing in that frame size and in a smaller frame size.

I'm trying to understand why this site (and others): http://www.encoding.com/what_are_the_best_flash_video_frame_dimensions recommend only the following values for smaller sizes:

384 x 216
128 x 72

when clearly others like:

320 x 180
256 x 144

also exist.

What is the mathematical reason behind recommending only these frame sizes?

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Does this question belong elsewhere? – Sid B Dec 21 '11 at 8:15
This question seems more broadcast and compression specific than AV Production! Inviting experts to a new site proposal Broadcast and Media Technologies which aims to capture more architectural and theoretical views around subjects like this. Join and invite others. – Dipan Mehta Mar 15 '12 at 20:08

2 Answers

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According to the site you referred to: http://www.encoding.com/what_are_the_best_flash_video_frame_dimensions

The math behind the "Best, Better, and Good" video formats are based on if both Horizontal and Vertical pixels are divided by 16 for best, 8 for better, and 4 for good.

Therefore 256x144 is best, while 384x216 & 128x72 are better, while 320x180 is good.

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The resolutions you mentioned are standard in Video codec development are CIF [352x288] and QCIF [176x144] (some other formats here: http://dvrsecurityforum.com/showthread.php?tid=30)

The reason why all these formats recommend multiple of 16 - is because MPEG compression has Macroblocks which are sized 16x16.

CIF = 22 x 18 Macroblocks. and QCIF is essentially half of it both sides.

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