[FFmpeg-user] Upmixing Dolby Pro Logic audio - still not possible?

Ted Park kumowoon1025 at gmail.com
Mon Apr 6 21:59:50 EEST 2020


> It is not that simple, it involves some complicated operations.

I thought the goal was to separate the stereo encoded surround from Dolby Surround/DPL, not up-mixing to a layout with more speakers than there are channels. Or are you saying that the decoding involves complicated operations?

I mean the operations do involve complex terms and if you find a DPL decoder plugin/library then it probably is better than doing it on your own, I was just saying all the information to implement a perfect decoder for the original Dolby Stereo Matrix-encoded formats is out there. In fact, I don’t think you can buy these decoders from Dolby anymore, they will refer you to one of the online virtual encoding/decoding houses and tell you that their software implementation is just as good as their rackmount units.

And while they transitioned from one algorithm/coding strategy/technology to another, they were pretty generous about letting reference material distribute freely, if you can’t find a dolby white paper it’s probably only because it’s so old, not because its proprietary. That’s all I meant, since the OP found what was there to be lacking. Not that writing a decoder/dematrixer(?) is a weekend project.

> Yes. The audio track in question is simply Dolby Pro Logic, not even
> DPL2.

>> ...you could get the matrix coefficients by
>> googling for them and do the math and get the separated channels by
>> hand.
> Any pointers to guides on doing this would be greatly appreciated.
> Thanks!

This is more of a conceptual overview rather than a complete specification of the stream, but it goes into some detail on how the encoder operates, and in turn, how a decoder would work, in inverse.
https://media.kumowoon1025.com/dolby/Assets/US/Doc/Professional/208_Dolby_Surround_Pro_Logic_Decoder.pdf <https://media.kumowoon1025.com/dolby/Assets/US/Doc/Professional/208_Dolby_Surround_Pro_Logic_Decoder.pdf>

Also check out Dolby’s GitHub <https://github.com/DolbyLaboratories>, though I doubt you’ll find anything that old.

Ted Park

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