MP4/AAC - Sound distribution of 'mono' files on homecinema audio systems?

[NoX1911]

Hallo,
i can save around 50% filesize when encoding MP4/AAC files (2h/q=0.1) as 'mono' instead of stereo (2xmono) but target systems may be homecinema devices (DVD player, PS3, 5.1 home cinema sound systems..) so it might be important that the sound doesn't come out of the center speaker alone. I want output speakers L,R not center. I'm not sure how 'mono' tracks get handled by such hardware. The question is can i go for mono and such hardware will output on L,R whatever happens? Is there any official center-only mode at all? Can i add metadata or something that will give a routing advice for the audio device?

The track actually is mono. Stereo (2xmono) would be just for compatibility.

What do you think.. should i go for mono or stereo (dual mono)?

[hello_hello]

Out of curiosity I took a wave file and mixed it down to mono, then converted it to AAC (single mono channel). I then muxed it into an MKV and opened the MKV with MPC-HC. I used ffdshow to decode the audio, looking at ffdshow's mixer matrix to see how it handles it.

ffdshow considers a single mono source as being a stereo input and splits it to the front left and right channels. In fact if I hovered the mouse over ffdshow's icon the tool tip said "Input: Stereo AAC" even though the audio track was definitely only single channel AAC.

I'd hazard a guess and say standalone devices would handle a mono audio source in exactly the same manner. An audio track would probably have to be multi-channel and have a designated centre channel for the centre channel to be used. It wouldn't make sense to do it any other way (least not to me).

[NoX1911]

Right, but if you pick 'libavcodec' instead of 'libfaad2' it shows otherwise. MediaInfo also calls it 'Channel positions: Front: C'.
http://www.abload.de/img/ffdshowvnfc.png

[pandy]

The track actually is mono. Stereo (2xmono) would be just for compatibility.

What do you think.. should i go for mono or stereo (dual mono)?

Mono should be not a problem but joint stereo should give same result from quality/bitrate point of view.

[hello_hello]

Right, but if you pick 'libavcodec' instead of 'libfaad2' it shows otherwise. MediaInfo also calls it 'Channel positions: Front: C'.
http://www.abload.de/img/ffdshowvnfc.png

It appears you're correct and ffdshow's mixer indicates it's treating it as a centre channel. I have no explanation for that but I'd hope a standalone player would be more clever.

Mono should be not a problem but joint stereo should give same result from quality/bitrate point of view.

I actually thought the same thing so I tested it. I downmixed an MP3 to a mono wave, then converted the mono wave to a new stereo (dual mono) wave.
Using the standard AAC and MP3 variable bitrate presets (foobar2000) I then converted both wave files to AAC and MP3. In both cases the dual mono AAC/MP3 was about 1MB larger than the mono AAC/MP3 and that was for a 3 minute song. Am I missing something?

[pandy]

if bitrate is identical this look very strange