[mythtv] [PATCH] AvFmtDec scanAudioStreams

[Taylor Jacob]

Quoting Daniel Thor Kristjansson <danielk at mrl.nyu.edu>:

> On Thu, 28 Oct 2004, J. Donavan Stanley wrote:
> ]By the way, can anyone point me to some specs for MPEG2 formats.  The
> selection
> ]of the audio track to use was based on a sampling of some DVD rips I had,
> ]however it's not right for ALL DVD rips.  I assume theres a rule to follow
> for
> ]always getting the main audio track for a given stream, I just don't know
> what
> ]it is.
>
> I don't know about MPEG2 in general, but with ATSC there is an
> AudioStreamDescriptor either in the PMT or the TVCT that tells you if
> the service is a major or minor service. Then to select between major
> services you can look at the language code.
>
> Unfortunately, this may not be a "full service" which means you may need
> to mix a major service with some minor services to get both the dialog
> and background sounds. (If it is a full service the descriptor tells you
> this too.)
>
> For details look at a_52a.pdf from atsc.com, at about page 120.
>
> DVB has a similar descriptor called an "AC-3 Descriptor" which is
> lightly described in a_52a.pdf at about page 125.

The PMT has all this information in the audio descritptors if you look at the
MPEG2-TS docs.. They may not be populated for DVB or ATSC since they choose to
place it elsewhere, but it could be shifted into the PMT if you have a more
powerful PMT re-write scheme I would think.

To get the specs you have to pull out your wallet.. If you are in the US you can
BUY (yeah don't make me get on my soapbox) then for I think 18 bucks from ISO..
If you are in Europe I think you buy them from the ETSI..  It has of this
information in there..