[Ffmpeg-devel] dts decoding broken?

[Justin Ruggles]

Ian Caulfield wrote:
> On 17/02/07, M?ns Rullg?rd <mans at mansr.com> wrote:
> 
>>"Andreas ?man" <andreas at olebyn.nu> writes:
>>
>>>We lose the ability to specify 2channel surround downmix (as Justin
>>>pointed out) and similar stuff, but that might be better to provide
>>>in separate flags anyway.
>>
>>What is 2-channel surround?  Something akin to Dolby Prologic?
> 
> 
> Basically it's a downmix of a Left, Right, Centre and Surround into
> two channels. The dolby surround channels could be specified as
> different channels to regular left/right (they're generally
> abbreviated to Lt/Rt rather than L/R), or a flag for surround downmix
> could be used. Would we ever not want to use this downmixing mode
> though?

Actually it's slightly different.  Essentially, it is Dolby Prologic.
In AC-3, for example, there is Lo/Ro which is a basic downmix of all
channels into left and right, and Lt/Rt which is a Dolby Surround
(a.k.a. Prologic) downmix.

In an LoRo downmix, you mix left surround into left, and right surround
into right.  In an Lt/Rt downmix, you mix both surround channels into
both left and right, but left is phase-inverted.