Why don't DVDs contain lossless data?

[mog08]

Mpeg-2 is not lossless, nor is AC-3. An audio CD is lossless, but a DVD is nearly always not. explain to me please.

[Guest]

DVD has video.

[scharfis_brain]

DVD needs to store about two to four hours of 720x576 pixels @ 25 fps or 720x480 pixels @ 30 fps.

this sums up to
7200 sec (2hours) * 720 (Horizontal)* 576 (vertical) * 3 (RGB) * 25 frames/sec = 209 GIGABYTES!
This equals to a datarate of 237 MegaBits per Second or 30 Megabytes per Second.

I hope the reason for lossy compression is clear now.

[mog08]

I get it that it's impossible for a DVD. what about movies we see at cinemas? Dolby audio is popular which is lossy, and videos are likely also lossy isn't it? Dolby doesn't have some type of lossless surround sound, I assume.

[Blue_MiSfit]

95% of movie theaters are still good old fashioned 35mm film.

Some are starting to transition over to 1080p, 2k, or 4k projectors - especially the film festivals, but most theaters can't afford the really high quality projectors necessary to facilitate digital cinema.

I'm not sure what compressed format is used to deliver digital cinema... I think I read up on it awhile back but it would make sense if they were using high bitrate MPEG-2, or something equally adept at preserving quality (admitedly at the expense of bitrate).

A lot of movie theaters use Dolby Digital, which is lossy, but its honestly an excellent audio compression format, especially for multichannel. Some also use DTS, and some use uncompressed multichannel PCM if I recall correctly. Keep in mind that these digital audio formats are used in conjunction with traditional film.

There are multichannel lossless audio codecs - I don't recall what they are called, but the HD-DVD / BluRay discs will eventually support these formats. There's a DTS version and a Dolby version, but other than that I don't really know.

And yes - video is just too freakin big to deliver uncompressed, or even lossless in essentially every scenario. A good lossy encode can be perceptually lossless to most people and display devices. Of course, this is not always the case with DVDs :)

Oh well.

~MiSfit