[MPlayer-users] newbie question: bitrate

[Yourself]

Quoting Yan Seiner (yan at cardinalengineering.com) as `YS'
Message date: 21 Mar 2003 at 06:32

YS> Could someone explain bitrate to me?   Here's what I'm trying to do:

YS> What exactly is a bitrate, and how do I go about calculating a bitrate
YS> suitable for such a low resolution?

Think of bitrate the amound of data being used to describe what's going
on in the picture/sound: The more data you use to describe, the better you
describe it and so you get better quality. Bitrate is usually measured
in Kbit/sec, which means how many kilobits ( = Kilobytes*8 ) are used to
describe one second of video/audio. So, in mp3 you usually have
128Kbit/s, which is 16KByte for every second of audio. If you have a 5
minute mp3, it will be approximately 5*60*16 = 4800KB or 4.7MB

What you need to do is, first of all, determine the length of the video
to be recorded. Say, it's 1 hour. Next you'll want to think about how
big you want the resulting file to be. if you want it about 500MB, then
you have to think like this: I've got 500MB to use for 1 hour, or
500*1024 = 512000KB to use for 3600 seconds. Which means 512000/3600 =
142.2 KB/sec. So if you want an hour of anything to fit into 500MB,
you'll need a bitrate of 142.2 * 8 = 1137Kbit/sec. This is your total
for video/audio. If you use mp3 for audio, you'll probably need 128 of
those for audio, which leaves you with 1009Kbit/sec for video.

The resolution of the output is not relevant to the bitrate. What
happens is: if you use a high resolution and a given bitrate, you'll
need much more data to describe it (and you won't have them) so you'll 
loose quality. Whereas if you use a lower resolution, you'll need less 
data, so with that given bitrate you'll get higher quality. (Well it 
isn't exactly so, but you get the idea)

YS> Note that I am not interested in stuffing a movie onto a CD; I'm not
YS> really concerned about how large the final product is.  I want it to be
YS> as small as the resolution warrants.

You will be the one to determine that. Encode small chunks at different
bitrates and see which one gives acceptable quality...

YS> Thanks,
I hoped i helped...

-- 
yourself
  
"Mind if I smoke?"
"Yes, I'd like to see that, does it come out of your ears or what?"