Web Video at 320x240, why?
 

We are looking at streaming video on the net and of course the first size that came to mind was the standard 320x240. Question is if I render it at a constant bit rate of 300k at 320x240, will it run smoother than a 640x480 version if they are both set at 300k? My thought was you are giving the movie a pipeline big enough to run at 300k but because there is more data for a 640 version it will chug along trying to play it. Am I right on this? Is that why every movie on the net is almost all 320x240?? Or does it not matter what the movie res is because I set it at 320? Thanks

if you set both frame sizes at the same 300kbps, they will both be pushing the same amount of data, one is just more compressed than the other... so it's a question of how your footage looks, do a bunch of test encodes for both frame sizes... full frame size may be pushing it at 300kbps, dropping the frame rate way down is how it's typically done... so talking heads at 7.5 fps will look a lot better than high-action stuff at 7.5 fps.

300 kbps means your video has 300 kilobytes of data per second. Whatever your screen resolution, that is how much data is being pushed through.

300 kilobytes is then divided among the number of frames you set per second.

So 2 things affect the "look" of your video when you set a data rate of 300 kbps. The pixel dimensions and the framerate. 320x240 at 15 fps will "look" better than 320x240 at 30 fps because that 300 kbps is "stretched" out over twice as many frames. Meaning there is less data per frame. Similarly, 320x240 at 15fps will "look" better than 640x480 at 15 fps because the 320x240 is able to use more bytes per pixel for clarity.

Setting 300 kbps affects the file size. Framerate and pixel dimensions affect the "quality" of the video.

kilobits not kilobytes, big big difference.

Whoops. :-) yes, big difference if you are trying to calculate what your file size will be in the end, but not for the basic concept.

8 bits = 1 byte. So 300kbps = 37.5 kBps or kilobytes per second. Which is then 2,250 KB per minute of video. Or to round it off, a little under 2.5 MB per minute of video.

But basically, if you are streaming 300kbps it will mean users need DSL or Cable to view it without much buffering.