[MPlayer-users] Re: AC3 5+1

[Corey Hickey]

D Richard Felker III wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
 >
>>This is what I get in mencoder:
>>==========================================================================
>>Opening audio decoder: [liba52] AC3 decoding with liba52
>>Using SSE optimized IMDCT transform
>>AC3: 5.1 (3f+2r+lfe)  48000 Hz  448,0 kbit/s
> 
>        ^^^^^^^^^^^^^^^
> 
> This means it's 5.1 AC3.
> 
> 
>>Using MMX optimized resampler
>>AUDIO: 48000 Hz, 2 ch, 16 bit (0x10), ratio: 56000->192000 (448,0
> 
>                    ^^^^
> 
> This appears to mean mplayer is playing it for just 2-channel. Like I
> said, mencoder might have put bogus numbers in the headers, but if so
> I'd be surprised if no one else had noticed such a bug before.
> 
> Anyone else have comments on this? (BTW if you just mail to me, no one
> else can read your mail so no one else can comment!)
> 

I was under the impression that the case here is that mplayer is playing
back the audio in "2-channel mode", either by the user specifying
-channels 2 or by default. In this case liba52 will decode the 5.1 AC3
audio into two channels (I get this from the manpage entry for
-channels). If I play a DVD with 5.1 AC3, I get the same messages.

I presume it goes like so:

left-front: intact
right-front: intact
center: mixed into both left-front and right-front
left-rear: discarded
right-rear: discarded
LFE: ? (either discarded or mixed into the front channels, I suppose)


I can play mencoder-created AVI files with AC3 audio in 5.1 by using
$ mplayer -ac hwac3 -ao alsa9 file.avi
-or-
$ mplayer -channels 6 -ao alsa9:surround51

In the latter case, however, there is a bug in the alsa output wherein
the channels "jump-around" whenever I seek, and might not stay in the
correct places. I usually end up with the positioning all screwed up.
Vladimir I. Umnov wrote a patch that fixed this a long time ago, but it
never was committed. You might look here for a more recent version:

http://mplayerhq.hu/pipermail/mplayer-dev-eng/2003-July/019891.html

I don't know if that is the same fix, though. Otherwise, you can search
the archives for it, but be aware that the old patch won't apply cleanly
to current CVS.

-Corey