You can fit 2 hours on but it is all going to be dependant what audio your are using. I use this formula.

Add the total minutes of video (if you are using motion menus in your authoring application include those)

600/total minutes of video = AVERAGE combined bitrate for video/audio

ie
600/120mins = 5.0Mbs

If you are using stereo Dolby Audio or MPEG audio at say 192Kbs then that would leave an AVERAGE bit rate of about 4.8Mbs for your video (set encoder for something like 7.0Mbs max , 4.8Mbs AVERAGE , 1.0Mbs low)

If you are using PCM audio then that is going to be about 1600Kbs so say about 3.4Mbs AVERAGE (but same max & low)

Vonhosen,
I've seen you post this formula before. It's a wonderfully simply little formula that's worked very well for me when packing a disk to the limit!
Question for you- Where does the 600 in the formula come from anyway??

Signed,
Math never was my best subject.

A 4.7Gbdisc has 37,600 Megabits available.
When I first started authoring DVDs I read that I should allow 4% for overheads (navigation data, still menus etc)

Take 4% from that & you have 36,096 (Make it a nice easy round number without losing too much & you have 36,000)

So we have 36,000 Megabits to divide equally amongst all the seconds in our movies that are to be included in our project. That would give us the average bitrate for all our movies (video & audio)

Because we are working in seconds (& that's a lot of numbers) we can make it easier so instead of working on 36,000/number of seconds if we divide both sides of the equation by 60 we get

600/number of minutes = average bitrate.

As I said earlier the 4% ovrehead doesn't include motion menus so you'd have to add them as movies.

I don't know about you but I'm quicker dealing with small numbers than big numbers. This method provides a fairly accurate way of maximising the available space on your disc, whilst maintaining quality. It's never failed me & that's why I pass it on.


A couple of other things of note

For compatability reasons when doing small projects I don't use as high a bitrate as this formula may allow. This is because I don't want the playback device pushed to the limit (it may result in skipping during playback)
The maximum combined bitrate you can use is 9.8Mbs but I would use a combined rate lower than that even if space allowed higher. Say 9.0Mbs. At that rate you shouldn't notice any quality hit but you are taking the strain off the decoding.

If you are adding multiple language tracks & subtitles, these will have to be catered for in your original figure for the AVERAGE bitrate.

Thats great guys-great information. Thank you so much.
But I've been tweaking the Max, Avg & Min as you've suggested, using a 5 minute test render- I'm still getting larger filesizes - larger than the DVDpal template.

I read in an old posting about some problem with Main Concept in this regard.
Was there a fix? or am I still doing something wrong??

Thanks again
Tower

For What it's worth and all...

There are a few bitrate calculators for those who would rather, though of course there's nothing wrong with the formula posted previously.

The only notes I would add to the discussion are:

1) if the source is clean enough you should be able to go below 3000 -- the MC mpeg2 encoder seems to loose it around 1.8 or 1.9, Ligos around 1.6 (though I've gotten it as low as 1.1 - 1.2).

2) At least in the US you have 2 things going for you, depending as always on your intended audience. If the DVD is intended to be played on a std TV with a std player, the picture is going to be limited anyway.

Last I heard there was one outfit in the UK producing a *very* expensive player that actually produced a digital out at or near the quality of the DVD -- the rest are limited by licensing, specs etc. to a clean but still aprox VGA resolution [there was a fear that you'd be able to film or otherwise record the screen & all the encryption methodology would be for naught.]

Not that most would notice, as the std TV here in the US is limited itself. The average person is so used to it, that you could visit probably 50% of the households and the existing picture controls will be off a country mile.

I'm not saying anyone should deliberately turn out shoddy work, but just a friendly reminder of something I've seen figured out on any number of retail DVD's -- no sense putting that much more on your plate then you can eat -- or phrased differently, there comes a point perhaps when the only person gratified by the extra work &/or quality is you. This isn't a bad thing; just something we should keep in mind as deadline approaches, & it always does, doesn't it?

I find the MainConcept encoder tends not to deviate too far from the AVERAGE setting whatever. I would imagine a lot to do with this is because it is a 1 pass VBR encoder.

If you were to download a free bitrate viewer utility and view your encoded file you wouldn't see huge up & down movements in the rate. The rate would stay pretty close to the AVERAGE you set.

2 pass VBR would perhaps produce more of a variation but MainConcept plug-in doesn't have that yet.

You can get a free bitrate viewer here
http://www.tecoltd.com/bitratev.htm