Seeking Quick Bitrate Calculation Tip

[Surf]

Hello,

I am looking for a quick way to determine what my final result would be as far as the bitrate is concerned. I need it to determine whether I should use one or two disk for the desired quality. This derived from the observation that if the bitrate drops below 4.00mbps, the movie looks like shyte in hi-def...

Example:

2hour16min movie occupies 4469mb. (I choose to limit the dvd-r size to 4470mb.)

{(2hrX60)+16min}X60 = 8160 seconds.

4469mb x 8(bytes)= 35752.

35752 / 8160 seconds = 4.38 mbps. ????

Please, I am not looking for precision, just a quick method to determine the one disk or two backup strategy.

TIA

[ammck55]

Doom9's homepage > Downloads > Calculators > Bearson's Bitrate Calculator

[Surf]

Thanks ammck55 for Bearson's which calculates CDs. My fault for not mentioning a word about DVD:p .

Anyone else have a quick math formula/instruction? That's all I'm looking for. Nothing precise.

[stephanV]

Originally posted by Surf
Hello,

I am looking for a quick way to determine what my final result would be as far as the bitrate is concerned. I need it to determine whether I should use one or two disk for the desired quality. This derived from the observation that if the bitrate drops below 4.00mbps, the movie looks like shyte in hi-def...


For this you only need one number; the length of video that youd still want to put on one DVD.Assuming you use 448 kbps AC3 audio with your video, your minimum total bitrate would become 4000+448 = 4448 kbps

4448/(8*1.024*1024) = 0.530 MB/s
4469 MB / 0.530 = 8428s = 2h 20m 28s <-- so this is the limit for 1 DVD with AC3 audio (not considering overhead)

for general formulas:

movie length to bit rate ---> [total bit rate (kbps)] = [target file size (MB)]*8*1.024*1024/[movie lenght (s)]

bit rate to movie lenght ---> [movie length (s)] = [target file size (MB)]*8*1.024*1024/[total bit rate (kbps)]

[Surf]

Thanks StephanV for the reply which realized a ooops for not taking the AC3 into account. So, let me give another example:

Limiting my dvd-r disk to 4470mb

movie = 2hour 16 min 00 sec.

movie(with audio) occupied = 5000+500 = 5500 mb.

Assuming NERO Recode uses average bitrate compression method, what will the average bitrate be in 1 disk(4470mb)?

[stephanV]

Originally posted by Surf
movie(with audio) occupied = 5000+500 = 5500 mb.
???


Assuming NERO Recode uses average bitrate compression method, what will the average bitrate be in 1 disk(4470mb)?

if you fill up the disk:

2h 16min = 8160s

using my first formula:
4470*8*1.024*1024/8160 = 4595 kbps for audio and video combined.

[Surf]

Sorry again. I was just making up an example. The 5500mb size is the original ripped movie which I need to compress with Nero's Recode down to fit into 4470mb. Now that you know the 4470mb size limit, the length of the movie, can you calculate what the shrunk bitrate would average out to be?

[stephanV]

i just did that :p

[Surf]

lol, nevermind, I got it, thanks!

In case anyone is interested in finding out the reason of my madness:

4470*8*1.024*1024/8160 = 4595 kbps for audio and video combined.

In future all I have to do is to divide with the number of seconds to find out the average bitrate. For myself I don't want it to dip below 4.00mbps and when it does then I'll resort to rip into 2 disks instead of jamming into one.