[MPlayer-users] Dolby AC3 question

[Corey Hickey]

Rohit Sharma wrote:
> Corey Hickey wrote:
>> 1. The mencoder config file is ~/.mplayer/mencoder
>> 2. The channels option doesn't have any effect with -oac copy -- the
>> audio stream is copied without being altered, so all the original
>> channels remain.
>>
>> Those don't actually have any bearing on your problem, but I wanted to
>> point them out.
>>   
>> There are usually several audio tracks on a DVD, some of which are
>> 6-channel and some are 2-channel. I'm guessing that when you use '-oac
>> copy' it's copying one of the 2-channel tracks. Offhand, I don't know of
>> any reason why that would be a different channel from the one you get
>> when you play the DVD. ...except if you use 'mplayer dvd://1
>> -dumpstream' to copy the movie to your hard disk before encoding it,
>> which you didn't mention.
>>
>> Anyway, send us the _entire_ output of the following commands (change
>> dvd://1 and movie.avi to whatever they really should be).
>>
>> $ mplayer dvd://1 -identify -frames 0
>> $ mplayer movie.avi -identify -frames 0
>>
>> -Corey
>>   
> Many thanks, Corey.
> For your comments, I think for now I need clarifications on only the
> following.
> 
>     * my ~/.mplayer/mencoder file does not exist by default. Should I
>       create it and put channels=6 in there?

You can if you want, but channels=6 has no effect with '-oac copy'. All
channels will be copied regardless of the channels option -- there's no
way to do otherwise without decoding and re-encoding the audio stream,
which would defeat the purpose of '-oac copy'. What you have to do is
select the track that has the number of channels you want.

>     * I use scripts created by acidrip which do have first step as
>       "mplayer -dumpstream" to cache DVD onto the HDD so that processing
>       is faster [compared to doing three passes on the DVD drive].
>       Apologies I didn't mention it earlier. How does dumpstream affect
>       6ch audio from a DVD? If it does make a difference then I shall
>       let acidrip developers know of it.

MPlayer and MEncoder read DVDs a bit differently from the way they read
a file. One of the other developers may be able to explain exactly why,
but sometimes the audio track selected will be different when playing
the dumpstream. Try 'mplayer stream.dump -identify -aid 128'. If that
isn't it, try '-aid 129', '-aid 130', etc.. The -identify option will
make mplayer print out all the audio IDs it sees:

ID_AUDIO_ID=132
ID_AUDIO_ID=133
ID_AUDIO_ID=134
ID_AUDIO_ID=137
ID_AUDIO_ID=128
ID_AUDIO_ID=130
ID_AUDIO_ID=131

...so try each of those if you want. You can recognize the number and
kind of channels in an AC3 track by looking for a line like this:

AC3: 5.1 (3f+2r+lfe)  48000 Hz  448.0 kbit/s

A DTS track will have this line:

Selected audio codec: [ffdts] afm: ffmpeg (DTS)

> Before I send the output across and flood your mailbox, just wanted to
> know answers to the two questions above hoping that they may just solve
> the problem.

No need to send them if what I wrote above solves your problem. Don't
worry about sending output in the future, though, since looking at the
output is the first step in most diagnoses.

> This may be an HTML mail. Please let me know if you are not OK receiving
> HTML formatted mails and I shall change composer format in my mozilla.

I find HTML email mildly annoying; some people really don't like it,
especially on mailing lists, so you ought to switch to plain text. The
mplayer mailing lists go so far as to automatically strip HTML from all
messages.

Also, please reply to the mailing list instead of to me directly. I'm
keeping you CC-ed because your first message had your address explicitly
in the reply-to field and I thought you might not be subscribed.

-Corey