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View Full Version : Dolby Prologic Revisited


Cyberia
9th April 2004, 02:55
Today I noticed several threads indicating that DVD2AVI somehow alters AC3 it demuxes and removed or altered the header information necessary for Dolby Prologic.

On the way home tonight, I realized I have the perfect system for testing this. I have a MidiLand decoder box connected to my computer via optical SPDIF. AC3Filter is configured to send directly to SPDIF.

I found a DVD with a Dolby 2.0 ProLogic track. When played by PowerDVD, my decoder box's Prologic indicator lights up. FYI: Not all DD2.0 AC3s are Prologic, several other DVDs/VOBs are identifed as DD2.0 but NOT as Prologic.

The Test:
DVD: BladeRunner (Directors Cut)
DVD2AVIdg: v1.77.3dg1.0.0RC2
SmartRipper: v2.41

I demuxed AC3s using SmartRipper and DVD2AVIdg....

BOTH AC3 files are identified as DD2.0 Prologic!

I have found several other Prologic DVDs and DVD2AVI demuxes them all correctly. So, unless someone can provide a DVD title, or provide examples, I think this issue should be crossed off the list.

KpeX
12th April 2004, 00:53
Pro Logic has nothing to do with any headers, pro logic is only based on the difference between the two channels of audio. Any two channel source can be upmixed using Pro Logic. As far as I know there is no accurate way for detecting pro logic in audio. Unless a demuxing tool reencodes the audio, pro logic will be preserved.