What makes DVD movie size?

[Josh]

Does anyone know why it is that some movies are bigger in file size? (I mean the movie only, not the entire dvd disc). Here's an example that doesn't make sense, and it seems there are a lot of movies that don't make sense.
A Muppet Christmas Carol is 89 minutes, but the movie is larger than Dumb & Dumber which is 106 minutes.
The Dumb and Dumber DVD could be copied entirely on one 4.7 GB dvd, menus, extras and everything. But Just the movie only of A Muppet Christmas Carol was over 5 GB. Any ideas as to why the difference? It seems that time is not the only factor. Oh, and A Muppet Christmas Carol Only had English Language and subs too, whereas Dumb and Dumber has multiple languages and subs. Just doesn't make sense. Thanks!

[Josh]

I still haven't found any answers, but this webpage is cool, it tells which movies you can do a full back-up on, movie only, and movies that are bigger than 1 dvdr.

http://members.optushome.com.au/cdromguide/

[atreides93]

Movies are typically encoded at a variable bit rate. This varies depending on the complexity of the image and the amount of pixels that change on the 720x480 screen each frame. So the final file size isn't just dependent on the movie length but the movie contents as well.

I've also noticed when encoding at one pass VBR using CCE that 4:3 movies tend to require more bitrate...also interlaced video requires more space.

[Gil T Pleasure]

So the final file size isn't just dependent on the movie length but the movie contents as well.

That is also true with VHS tapes. If you record 2 hours on a T120 VHS tape in SP mode, the entire tape is used up. But if you record the same 2 hours in EP mode, it only uses a third of the tape.

[Josh]

I understand better now, thanks.

[Josh]

I'm not entirely bought on the movie size thing. I really do believe that they do tricks to make the movie size better. Take for example the movie The One, that has very high video quality and great sound, yet the movie only is 2.58 GB. I think that somehow they make the movie size bigger. Kind of like the VBR thing with DVD2SVCD. The more passes the bigger the movie size, but after a certain point (like 4), the quality doesn't go up any furhter, just the size of the movie.

[Kandor]

that is not true. the size goes up if you choose a higher avrage bitrate.
so the size is dependent on the avrage bitrate and how compressible the movie is.


so if you make more passes it only means that it will use the bitrate it can have better. it means better quality. it means more bitrate where it is needed more and less where it is needed less.

[Josh]

So they have no sneaky tricks, it's all bitrate then. I guess I can see that. It just doesn't always make sense when you compare 2 movies that look equal in everything, and one is 4.3 GB and the other 7.35 GB for example.

[Gil T Pleasure]

Yes, it's all in the bitrate. In general, the higher the bitrate the better the picture quality and the less video a disc can hold.

However, the converse is not alway true. You can have a good quality video using low bitrate. How? Well a fast moving scene (ex. sports) requires a high bitrate to produce good video quality, but a slow moving scene (ex. newscast) only needs a low bitrate to produce good video quality.

Related link:
How does MPEG work? (http://www.vcdhelp.com/mpeg2.htm)