How to calculate bitrate for cropped source

[drak23]

Anyone:
I've been trying to see if FitCD could do this but I'm having trouble figuring it out. A number of the shows I capture these days broadcast in letterbox, with black bands at the top and bottom. I'm cropping these out in TMPGEnc so that the encoding focuses on only the source (I turn on masking to preserve the original aspect ratio).

I take off about 25 lines from both top and bottom (source as seen by TMPGEnc is 352x240, about 43 minutes). When I use a simple calculater like the one on this site, I get a file that is about 775MB. I want to max out the size to around 800MB for my 80-min CDs.

It would also be nice to have the option to calculate for non-standard SVCD specs (higher bitrates than normal SVCD) to maximize my DVD player's capabilities.

Can anyone advise on this, or point me to a tool or guide?

Thanks,
Drak

[adam]

Filesize equals bits per second x total number of seconds...period.

How you resize or the size of your black bars may affect your quailty at a given bitrate but it will not affect filesize and thus there is nothing to "calculate."

Whether your source is fullframe or widescreen, 720x480 or 352x240...it doesnt matter. At the same bitrate it will always be the same size.

In my experience, FitCd is incredibly accurate if you set it up correctly. Make sure that everything is set up exactly as you are encoding. For example if you tell it that you are multiplexing with bbmpeg and that you are using the SVCD scan offsets when you really aren't, then your filesize will be off by as much as 40MB's.

Also don't forget that Vcds and Svcds have additional overhead that is added during authoring. For vcds its around 5mb's and for Svcds it can be 10mb's or more so your filesize right now isn't quite as far off as you think. If you want to get the exact size then in Fitcd set the safety space to 0, but you'll be sorry if your mpg ends up being 15mb's too big to fit on your disk.

"It would also be nice to have the option to calculate for non-standard SVCD specs (higher bitrates than normal SVCD) to maximize my DVD player's capabilities"

Bitrate is independant from any standard. In FitCD it will take your standard into account when calculating how much overhead will added, but the bitrate level itself is simply a matter of comparing playtime + additional overhead against the total capacity of your media(s.)

Fitcd will calculate the bitrate to fit on the size of your media, whether the resulting bitrate is standard compliant or not.

[drak23]

Adam:
Thanks for the informative post - much is clearer now. Something else must have changed in the last file I encoded so that it came up short. I'll give it another shot, and tinker with FitCD a bit more.

Regards,
Drak