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

Andy Furniss andyqos at ukfsn.org
Sun May 27 20:13:08 CEST 2012

Joshua Tidsbury wrote:
> 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.

Apologies for butting in - but you seem to have lots of experience with ac3.

Am I missing something obvious with ffmpeg, or is there no way to 
specify a drc profile eg. film standard.

It would be handy (for my ears at least) to reduce with metadata full 
range sources, but I can't see any encoder option for this. I know drc 
is implemented for decode - is there a way when encoding?


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