Why can commercial DVDs hold 2 hours of video footage while home made DVDs can only hold one hour comfortably?

Question

I find that when I burn home movies and such that I have to drop the resolution quality a great deal if I want to squish 2 hours in there - Yet the ones we buy in stores hold not only the two hours, but even extras.
I use Ulead video editing software, but think this is pretty consistant with any program.

Thanks in advance for any coaching you might have!

Answer 1

Commercial DVD's can by double layer and can hold at least 8.5GB instead of the 4 of a normal recordable DVD.

Answer 2

I am not a professional video editor or anything like that. What follows is from my own experience burning DVDs and general knowledge of video/electronics. I believe there are two reasons. One is compression and two is media.

Because I don't trust DVD quality I back up every movie I buy and only play the copies. Anyway, in doing so, I've noticed that some movies of the same lentgh (let's say 90 minutes) will fit either on a regular DVD (4.7 GB) or have to be burned to a Dual Layer DVD (8.5 GB). I imagine it has to do with the amount of compression used. Because I don't want to lose any quality I do not let my software compress my copies and that means I use a lot of DL DVDs which are more expensive.

If you're burning your home movies to standard DVDs and the resolution is poor, I would think it is because they are being compressed too much.

I also imagine there are different compression softwares out there and that they are not all equal. It may be that if you're using a cheaper video editing software, the compression part of it is not up to snuff.

In copying my movies, i've also noticed that most of what fits on a standard DVD is either documentaries or French movies. So far I have not been very impressed by the averrage transfer of french movies and it could be partly because they use too much compression. Historically, documentaries have not had the same level of image quality as theatrical releases (it's a lot harder to shoot a documentary in 35 or 70 mm), thus ending up with transfers requiring fewer GBs.

Although some of those "educated" thoughts could actually be facts do not take them as such unless confirmed as such by someone else.

But I do hope it helps.

Answer 3

If the movie is more than 90 min, you will need a double-layer disc

Typical bit rate for DVD movies is about 6 Mbits/s
So a 5 GB DVD will hold about 100 min of video and audio

To squish 2 hours, set the bit rate to about 5 Mbits/s.
Always use VBR (instead of CBR) it should give you better quality.

Answer 4

When you compress movies for home made DVDs, you are using a basic encoder which is a "real time" single-pass method. This method is limited in the degree of compression achievable for a given quality level.

Professional DVDs use multi-pass compression and the amount of compression and bit rate is varied according to the source material. Scenes which can be compressed easily (slow-moving material with not a lot of detail) are alloted fewer bits so more demanding source (fast action, high detail) are given more. Multiple "passes" through are used to optimize the results (some DVDs are more successful than others, as can be determined from reviews in high-end video magazines). This process takes much more time than home-video compression.

However, for movies of more than 90 minutes, it is generally better to use two-layer media and less compression.