why doesnt reducing frame rate and shrinking video dimensions decrease the filesize?!

boskins · #1 (**permalink**) 03-03-2009, 11:01 AM

i Have a series of videos which are to be published to the web. i run a mac, the videos are .movs and i am using iSkysoft's Video Converter.

I am trying to get the files size to a minimum. The problem i am having is thus: the only setting which seems to have any effect on the file size is the altering the bitrate.

Reducing the framerate does nothing - that makes no sense to me - can someone explain?
shrinking the dimensions of the video also does absolutely nothing - can someone please explain this?

The videos are to be imported into flash as embedded swf (which significantly increases file size) to have animation layered on top - i need to know i have done everything within my power to get these videos as small as possible.

Any input or advice would be very much welcomed!!

thanking you in advance

Danny

Mike Thorpe · #2 (**permalink**) 03-03-2009, 11:15 AM

That's to be expected - the bitrate is the overall size of the file. For example, if you had a video that was a minute long, that had a bitrate of exactly 500kbit/sec, then...

500 divided by 8 (because there are 8 bits in a byte) = 62.5 kiloBYTES a second

62.5 (kilobytes) multiplied by 60 (seconds) is 3,750.

So your 1 minute, 500kbit video would ALWAYS be 3,750 kilobytes in size (or 3.66 megabytes) regardless of resolution.

By setting the bitrate, you're effectively saying to the program - "I want my file to be this size please, so compress the file as much as you need to to make it go to that size"

Shrinking the resolution just means that the encoding program doesn't need to compress your video as much. If you shrink the video, reduce the bitrate as well. That's the only way to reduce the file size.

boskins · #3 (**permalink**) 03-03-2009, 11:17 AM

thanks a lot!

same with the frame rate?

Mike Thorpe · #4 (**permalink**) 03-03-2009, 11:19 AM

Originally Posted by boskins

thanks a lot!

same with the frame rate?

Yep! The rate is usually set at kbits per second, not kbits per frame. If you've got less frames in it, it just means that they won't need to be compressed as much.

boskins · #5 (**permalink**) 03-03-2009, 11:21 AM

Mike, my man!