[FFmpeg-user] AC-3 Dolby Digital 5.1 Encoding

[Joshua Tidsbury]

On 2012-05-27, at 11:36 AM, Chase Patterson wrote:

> I guess you really have to guess what downmix option you want to use,
> as I know my stereo surround sound system I use with my TV has tons of
> options, e.g. Dolby Digital (not downmixed), Dolby Pro Logic, Stereo
> Surround (downmixes to stereo, then mirrors R and Rs, mirrors L and
> Ls, and combines both for C), and many more.

Oh yeah, there's a million awful things that home set top boxes and receivers can do to your mix.

Thankfully, most folks will either likely be listening to the 5.1 mix via Dolby Digital, or a stereo downmix (utilizing the mode described in your metadata, hopefully). If you create a ITU downmix in your DAW that folds C (at -3 dB) to L and R, and folds Ls and Rs forward to L and R respectively with a -3 dB gain reduction, and LFE at -6 or so to L & R, you can at least test the Lo/Ro option while you are mixing. At least then that version will be predictable. Without a plugin that mimics the Lt/Rt downmix process, that's much harder to guess.

So I'd set up a simple ITU folddown to check your mix against while mixing, and then use mode 2 downmix (Lo/Ro). At least that way you can hear that final result while doing the mix.

Take care,
Josh


Joshua Tidsbury | CTV Television
t 416.384.7253 | m 416.433.3968 | joshua.tidsbury at bellmedia.ca