[FFmpeg-user] mono or stereo? ffmpeg converts or phone?

[Sean Darcy]

On 04/28/2014 03:04 AM, Carl Eugen Hoyos wrote:
> Sean Darcy <seandarcy2 <at> gmail.com> writes:
>
>> So for a bitrate of let's say 48000, am I better off
>> converting to mono in ffmpeg ( -ac 1 ) or leaving it
>> stereo and letting the phone convert it?
>
> You may be better off (and if playback is only mono, you
> don't loose anything) but please understand that you cannot
> double the quality / half the bitrate.
> The chosen encoder is much more important, if your phone
> does not support opus, make sure to choose libfdk-aac.
>
> Carl Eugen
>

I don't have an audio book reader that can read opus installed on my 
phone. I don't even know if there is one. I do use opus for voip: it's 
really amazing.

But back to the OP. I am using libfdk-aac. I understand that 24000 mono 
will not equal 48000 stereo.

My real question is: how does ffmpeg downmix 2 -> 1. I assume it doesn't 
just take one channel. Does it "average" in some way the two channels?

I also assume whatever ffmpeg does, it does it better the android code 
on a phone doing it in realtime.

sean