Quantcast Bitrates: File Size Wrong: the Problem Seems to Come from Calcumatic - digitalFAQ.com Forums [Archives]
  #1  
11-30-2003, 07:18 PM
Dialhot Dialhot is offline
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Hi guys,

We often blame CQMatic because it gives videos a little above the target. I personnaly use to do my prediction with an audio bitrate above the one I really want (160 for 128, 128 for 112...).

I just discover that the problem isn't in CQMatic but... in Calcumatic !

I have an other tool that is called "dvtool" and has an internal bitrate calc that I used today.
Let see what happened :

- I have a 116 min long movie that I predicted with Calcumatic for a 90min CD. With audio at 128, Calcumatic gave me a bitrate of 931.

- I encoded the movie normally with Cqmatic and this average bitrate of 931. The m1v was 809 Mb long.

- So I have 91 Mb left on my CD for the sound. I open DVtool to find what audio bitrate I can use to have a 91Mb long audio file. The tools give me : 112 ! And it also gives me the average bitrate for an audio at 121 : 929. For audio at 128 it gives me avg=912

In sum : calcumatic gives for an audio bitrate of 128 the same avg that dvtool for audio at 112. And when I encode the file with Cqmatic and avg at 931, I have to encode audio at 112 to enter in my target.

Conclusion : Cqmatic is right ! That's Calcumatic that we need to change !

You can find dvtool there :
http://www.musclesoft.de/combatman/sindex.html
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  #2  
11-30-2003, 09:27 PM
kwag kwag is offline
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Hi Phil,

If you look at the result of CalcuMatic, you'll see that the values are in KB. Not in MB
For a movie of 116 minutes and a target CD of 900MB, the returned values of CalcuMatic are 810,240KB for video and 111,360KB for audio.

If you do the audio math:

First, 111,360KB / 116 Minutes = 960KB per minute.
So then 960KB / 60 = 16KB per second.
And last, 16 * 8 = 128, which is 128 KiloBits per second.

Which is what you want, based on the space left

-kwag
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12-01-2003, 05:00 AM
Dialhot Dialhot is offline
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Kwag, read again my post : I never talk about free space but I'm talking about video bitrates.

For 116 minutes on a CD90 Calcumatic gives me a avg birate of 931 with the audio at 128. For the same thing DVtool gives me 910. And with audio at 112, DVtools gives 929.

Why such difference ? I don't know (I agree with your maths). But the fact is that when I encode at bitrate 930 I obtain a video file that left me on the disc just enought space for encoding sound at 112. As I always do my prediction with an audio just above the one I plan to use, I wonder if I can avoid that just by using DVtools insteed of Calcumatic.

I will check the file sizes given by DVtool because it gives them also. Perhaps we will understand where the difference between the two softwares comes from.

Note: 810,240KB + 111,360KB = 921600KB = 900MB. That means that you do not take any security margin ? Or do you consider that a CD90 contains 915MB and not 900 ?
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12-01-2003, 05:39 AM
kwag kwag is offline
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Hi Phil,

I calculate to the max, without (S)VCD overheads, etc. If you take a look at the calculations given by MovieStacker, FitCD, Bearson's Bitrare calculator and compare them to CalcuMatic, you'll find that they are very close. Actually, Bearson's gives exactly the same result as CalcuMatic. So I believe DVTools math is wrong

-kwag
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