Video size calculation

[Fmazzanti]

Hello everybody,
I'm trying to use DVD2SVCD to encode my DVD to DVD-R, but I'm afraid the question I post applies equally well to SVCD encoding with this WONDERFUL tool.
The story is that I want to find out what is the Average bitrate I must set in the Bitrate tab to get a video stream of a given size (only the video, not the audio). So let's imagine I want to encode a stuff containing 2 audio tracks and one video stream. Also I want the video stream to be of a given size, let's say, 3800Mb (remember I encode to DVD-r). Also let's say I know that the 2 audios is going to take 500Mb (I do not encode them, simply keep the .ac3 files). The question is: what's the appropiate Average bitrate I must use?
I think I can do it in the following way:
call 'x' the bitrate in Kbits per sec.
call 'l' the length of the movie in secs.
Then x*l = Kbits that will take the movie.
Now I multiply it by 1000 to get it in bits, divide it over 8 to convert that to bytes, and finally divide it by 1024*1024 to convert form bytes to Kbytes to Mb. This formula reads in the end:

Mb = x*l*1000/(8*1024*1024)

Now I want to invert this, since I know what I want the size of the video to be (the Mb in the lhs) and am looking for the bitrate (the x). That leads me to

x = 8*1024*1024*Mb/(l*1000)


which is the bitrate at which I must encode the video stream (only the video!) to recover the size I want (the 3800Mb I said before).

Now how do I do that in practice? I would fire up DVD2SVCD, and in the bitrate tab set the Average bitrate to the value 'x' I've just obtained. However, D2S will process also audio tracks. Well, then I only have to select the 2 audio streams I want to copy, and increase the 'CD size' value to 3800 (=size of video) + 500 (=size of two audios). In this way, D2S will first extract (once again) the audios, discount their size from the 'CD size' value, which would give me 3800Mv back for video encodeing at the bitrate I set to get exactly this size for the .mpv file.

Would you say that works in this way? I'd like to know your opinions...

Thanks.

[winxi]

Hello!

I think that your calculation is right.
I have never tried to create a DVD-R with DVD2SVCD, but wouldn´t it be much eaysier to
-check "don´t make images" under the CD Image tab and
-check "Do not convert audio" under the Audio tab and
-choose the complete size of your DVD-R (in your case 4300, if i understand you right) under the Bitrate tab.

This way you won´t have to calculate anything yourself :).

greets, winxi

[Fmazzanti]

Hi,

Originally posted by winxi
Hello!

I think that your calculation is right.
I have never tried to create a DVD-R with DVD2SVCD, but wouldn´t it be much eaysier to
-check "don´t make images" under the CD Image tab and
-check "Do not convert audio" under the Audio tab and
-choose the complete size of your DVD-R (in your case 4300, if i understand you right) under the Bitrate tab.

This way you won´t have to calculate anything yourself :).

greets, winxi

No, nain, niet... I certainly check 'don't make images' since I will feed the output of the whole process to a DVD authoring tool. I also check 'do not convert audio', but (as far as I can see) D2S doesn't let you encode without checking at leat one audio track, so you have to include in the whole process at least one.
Besides, I think that setting the complete size of the DVD in each of the 'CD size' tabs is not enough, since I would say this is not the only thing that limits the size of the output file: if you convert a 1 hour movie and tell D2S to fill one 800Mb CD, wirh a low bitrate (300 or so, let's say) it will generate a CD image that will not take the whole available space on the CD. Why? Because D2S feels it can satisfy your bitrate requirements without having to fill the whole CD.
And that's exactly what happened to me a couple of times! I left the bitrate to 4500, set the CD size to 4300 and ended up with a video+2audios that filled only 3700Mb... thus wasting some wonderfu, 800Mb in my DVD-R. That's why I try to find the best Average Bitrate I must use to have a video file the size I want...
And YES, probably there are easier ways to do this, but as I said in my other post, I *love* D2S ;)

BTW, any good bitrate calculator suitable for this around?

[markrb]

Your way works well most of the time. The problem comes in when the audio bitrate is higher then 384. DVD2SVCD does not have a calculation for a 448 bitrate which is becoming more common on DVD's. When you find the audio is higher then 384 you will need to adjust the cd size a little lower to compensate for the larger audio file.

You are also going to want to modify the bitrate limitors on the bottom of the bitrate tab. Make Min 0, make Max 9000(or 9500) and make MAX AVG 7000. The Max Avg needs to be high enough to allow DVD2SVCD to fill the disc. If you limit this setting you force DVD2SVCD to use a lower setting then it can if room allows.

How do you get 4500 for a size? The max that will fit on DVD-R is 4.38GB's.

Mark

[Fmazzanti]

@Markrb,
I'll try what you said, which is obviously the simplest way to go... stupid me :mad:
BTW, 4.38Gb*1024 Mb/1Gb = 4485Mb whish is approx 4500.
Have fun and thanks!