[MEncoder-users] losing 5.1 audio on -oac copy transcode

Wes Morgan morganw at chemikals.org
Tue Sep 23 22:40:24 CEST 2008

On Mon, 22 Sep 2008, Dan Shoup wrote:

> I did not realize that.  I did some "listening tests" and my transcoded 
> file played with no options in mplayer (or played in GBPVR or VLC media 
> player) comes mostly through the center channel with a little on the 
> back speakers...but it is the just quality periodic noises, definitely 
> not 5.1.  If I play it on mplayer with -afm hwac3 -channels 6 I hear 
> lots of very realistic sound on the back speakers.  So I can not say for 
> sure whether my receiver is truly producing 5.1 as it indicates, but it 
> is a big step up in sound quality so I'm pretty sure it is.  Any other 
> thoughts?

If I use the "-channels 6" option when ripping, "file" reports that the 
resulting AVI has the proper number of channels. Dumping the AC3 streams 
from the AVI's produced with and without "-channels 6" give streams that 
identify themselves as:

ATSC A/52 aka AC-3 aka Dolby Digital stream, 48kHz,,complete main (CM)
3 front/2 rear, LFE on,, 448 kbit/s reserved Dolby Surround mode

The files themselves are not identical. Regardless, playing the original 
DVD or the resulting AVI with "-channels 6" or not, mplayer always says 
"AUDIO: 48000 Hz, 2 ch, s16le, 448.0 kbit/29.17% (ratio: 56000->192000)". 
However, my old sony receiver, when using the optical output from a 
DSM-520, identifies the streams as dolby 3/2 regardless of what the AVI 
header or stream header or whatever claims, and also correctly calls an 
AVI with mp3 audio "PCM". I have not yet tried a file with a true AC3 
stereo stream for comparison.

>> From: scowl at pacifier.com> To: mencoder-users at mplayerhq.hu> Date: Sat, 
>> 20 Sep 2008 08:49:25 -0700> Subject: Re: [MEncoder-users] losing 5.1 
>> audio on -oac copy transcode> > On Fri, 2008-09-19 at 19:33 -0500, Dan 
>> Shoup wrote:> > Anyhow, I tried this and I get the same result...the 51 
>> audio is there, but no player seems to recognize it by default. I can 
>> only get 5.1 audio played back if I force mplayer using afm hwac3 
>> -channels 6 and I have no way to force this in GBPVR (my preferred 
>> video player).> > How do you know for certain that DD 5.1 audio is 
>> there? What players> have you tried it on? > > Some receivers will lie 
>> and say they're playing 5.1 audio when they> aren't which sounds likely 
>> since you're using hwac3. We see this> confusion all the time when 
>> people declare their receivers "smarter"> than others because they see 
>> 5.1 audio when more truthful receivers> "can't".> > If the AC3 packets 
>> aren't tagged with 5.1 then these players/receivers> are lying about 
>> the audio they'
> re seeing and mplayer is simply telling> you the truth.> >

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