x264 bitrate calculation

[MSlv]

What would be the recomended bitrate for 2hDVD-to-700mb conversion?

[Ark]

Originally posted by MSlv
What would be the recomended bitrate for 2hDVD-to-700mb conversion?

Erm...maybe using all the space that you have on a CD-ROM? :)

[MSlv]

You're not helping.
:D

[Ark]

Well, if your target is 700mb (which is very low bitrate for a 2h movie at a decent resolution unless it is 2001 a Space Odissey) i think you have to simply use all the space you have, whatever bitrate it ends up, since in all cases you can't do better with that space limit...

[MSlv]

so, how do I set a target size? I'm using VirtualDubMod and all I can set is bitrate!
pics:
http://www.imagehosting.us/imagehosting/showimg.jpg/?id=142260
http://www.imagehosting.us/imagehosting/showimg.jpg/?id=142264

[Ark]

That's more tricky, as x264 doesn't have "target-size" encoding type (yet i think), so you have to guess.
I think for 2h a 700mb cd (not xcd) would give something like 600-650 kbps, but then there is source compressibility.
Try a first pass with xvid at q2, that will give you a rough estimation.
If it end up larger that desired (probably), made another 1st pass at q3, look at resulting filesize in the stats window, until you get close to 700mbyte.
It's a pain i know, but for now i think it's the only method...

[MSlv]

[edit]

[sysKin]

Originally posted by Ark
That's more tricky, as x264 doesn't have "target-size" encoding type (yet i think), so you have to guess.
I think for 2h a 700mb cd (not xcd) would give something like 600-650 kbps, but then there is source compressibility.
Try a first pass with xvid at q2, that will give you a rough estimation.
If it end up larger that desired (probably), made another 1st pass at q3, look at resulting filesize in the stats window, until you get close to 700mbyte.
It's a pain i know, but for now i think it's the only method... Yeah, you can do all that. Or you can use a calculator and divide desired filesize by movie length.

[MSlv]

Originally posted by sysKin
Yeah, you can do all that. Or you can use a calculator and divide desired filesize by movie length.
You mean divide 716800(kB) by 2(h)? That means <400kbps!

[stephanV]

?

716.800*8*1.024 / 7200 = 815 kbps... so if you use 5.1 ac3 audio i guess your right

[MSlv]

thank you very much stephanV. Just a question:
*8 to get to bits from bytes, right?
and what for is *1024?

[stephanV]

yep 8 is for byte-->bit

1.024 (not 1024) is for the change in k... one kilobyte = 1024 bytes while one kilobit = 1000 bits (in most cases)

1024/1000 = 1.024 :)

[MSlv]

I get it now. Thanks for the info.

[Sergejack]

Bitrate is birate; it's not a matter of codec.

[Ark]

Erm... i'm not very good at math...:D