Thread: Bit rate formula

Quicktime Pro doesn't have a way to specify a file size, just the bit rate. I want my movies to come out to 700MB so that they will fit onto a CD. In h.264 encoding, how do I calculate the bit rate to do that?

Filesize in Mb = (((Video bitrate in kbps + Audio bitrate in kbps) X (Runtime in secs)) X 1000) / 8 / 1024 /1024

and add about 5% overhead

but chances are you're using variable bitrates on both the audio & video
so this isn't going to be very accurate

to be accurate, you'll need to do what's called a "2-pass encode"
Is this an option in quicktime pro?


*edit*
tutorial straight from apple
step 6h seems to suggest 2 pass encoding is possible
http://www.apple.com/quicktime/tutorials/h264.html

Thank you very much.

I always use two pass encoding, it's much higher quality. So slow though, I wish I had a H.264 hardware encoder :-( Oh well.

Originally Posted by ninja9578

I always use two pass encoding, it's much higher quality.

ysou should be able to encode video to a predetermined size, in that case (that's one of the advantages of 2 passes)

I can't figure out how to do that, I don't think it's a feature of Quicktime.

I got another question: When Quicktime does the Export, is the .mov the same as a .mp4? Apple TV won't play a .mov, even if it's H.264 encoding. Can I just change the extension?

bear in mind that I'm not an Apple guy (haven't used a Mac since System 7)
but .mov (MooV) is Apple's own proprietary container format for mpeg 2 & 4, and is quite old
AFAIK, mov doesn't support mpeg4 part 10 (ie. mov does not support the newer AVC video codecs including H.264)

.mp4 is an international standard container for all mpeg4 formats, (including part 10) and is heavily based off of apple's mov file format

where you can, use mp4, as it's newer, is an ISO standard, and is properly supported cross-platform

you may be able to just change the extension, try it
but chances are there's an option somewhere in QT to make mp4 the default container