2.0 and 5.1 on same DVD

[zerohash]

Dear Sir,
i have seen many movies which have 2.0 and 5.1 audio in same DVD and in same language.Why do they encode two audio tracks when one can enjoy 5.1 in a streo TV.What is exact reason they put two audio on same DVD.What difference will it make to a viewer listning 2.0 and 5.1 on a stereo TV.

Thanking You.

Zerohash.

[E-Male]

I've once read that the 2.0 track has better prologic than the 5.1 mixed down by the player
it also might be the dvd-companies don't trust downmixes by players in general

maybe someone else got some more info on the subject

[mpucoder]

Usually it's not the same content, but has commentary. But if it is the same content the person in charge of audio encoding wasn't happy with the 5.1 "suitable for Dolby ProLogic" sound. 5.1 has a bit which says whether or not a downmix to stereo would be suitable for Dolby ProLogic decoders. In order to make a 5.1 track like that certain compromises take place. If the audio encodist insists, and there is room in the bit-budget, seperate 5.1 and 2.0 ProLogic tracks are encoded.
You're right about one thing, though, it doesn't matter to a 2 channel only listening environment.

Edit: I shouldn't take so long to type, E-Male beat me with the short version.

[E-Male]

but the long version is more enjoyable to read :)

[thirty6hex]

You would be surprised at how many clients desire a 2ch and 6ch mix. I've noticed that the separation and attenuation of the channels is sgnificantly reduced in a 5.1->2ch downmix in even the best circumstances, not to mention that you are relying on *their* hardware to do it.

If you're smart, you do all you can to not rely on the hardware in DVD land as a rule. 5.1 and 2ch AC3 are totally kosher in bitstream format, but as soon as you downmix, you are hitting spots in the DVD spec where 3'rd tier manufacurers are allowed to cut corners.

A couple of our other little crib notes are:

1) Toshiba has the slowes optics ever, but they play anything you stick in em
2) Sony optics suck, don't get a DVD-R near 'em unless they're a new unit
3) An Apex, Aiwa, Phillips, GE, Sears, or any other house brand all generally use the same optics with the same warranty- 6 months. They usually die after that.

As far as the space goes, you're looking at under 100 megs for a relatively good 2ch AC3 for an average feature. If you're worried about 100 megs: re-encode something, cuz you done screwed up.